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Aldehydes, ketones
and
carboxylic acids
By –
Mr. Pranav A.
Galgale
PGT Chemistry
Organic Compounds having >C=O group are called carbonyl compounds. It's general formula is Cn H2nO (n = 1, 2, 3......)
Carbonyl compounds are grouped into two categories.
C = O
H
Aldehydes (also known as formyl group). It is a monovalent group (only one bond to get attached with carbon
chain)
Ketones C = O its both the valencies are satisfied by alkyl group. It is a bivalent group.
– C – OH
||
O
– C – NH2
||
O
– C – O – R
||
O
– C – X
||
O
– C = OH
|
O
–
+
– C = NH2
|
O
–
+
– C = O – R
|
O
–
+
– C = X
|
O
–
+
– C –
||
O
These groups contain but still they are not considered as carbonyl compounds as carbonyl group take part in resonance
Nomenclature of aldehydes and ketones
The common names of most aldehydes are derived from the common names of the corresponding carboxylic acids by replacing
the ending –ic of acid with aldehyde.
Names are given from name of source in Latin or in Greek
e.g.
Formaldehyde – Derived from formic acid present in ant sting (Greek: Forma – Ant)
Propionaldehyde – Derived from propionic acid (Greek: Propion – Butter)
Butyraldehyde – Derived from buyric acid (Greek: Butyr – Butter)
The location of the substituent in the carbon chain is indicated by Greek letters a, b, g, d, etc.
Nomenclature of aldehydes
Common system
Nomenclature of ketones
The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group. The locations of
substituents are indicated by Greek letters, a, a’, b, b’ and so on….
e.g.
C – C – C – C – C
||
O
a a’b b’
IUPAC names
Aldehydes –e of alkanes replaced by –al
In case of aldehyde group attached to cycloalkanes or benzene ring then word carbaldehyde is used as suffix in both the systems
Ketones –e of alkanes replaced by –one
Remember priority series:
– SO3H used as suffix (sulphonic acid)
– COOH used as suffix (–oic acid)
Rest for all functional groups used as prefix
If aldehyde and ketone both groups are
there, then name aldehydic group is written
in suffix (–al) and name of ketone is used
as prefix (–oxo)
CH3 – C – H
||
O
– C – H
||
O
CH3 – CH = CH – CH2
|
CHO
|
CHO
CH3
CHO
NO2
12345
1
2
Common system IUPAC system
Acetaldehyde Ethanal
Cyclohexanecarbaldehyde Cyclohexanecarbaldehyde
pent – 3 – enal
2 – methylcyclopentanecarbaldehyde
o - nitrobenzaldehyde
o - nitrobenzenecarbaldehyde
4 - nitrobenzaldehyde
o - nitrobenzenecarbaldehyde
________
b – methylcyclopentanecarbaldehyde
Aldehydes
a
b
CH2 = CH – CHO
CH3 – CH2 – CH2 – CH2 – CHO
CHO
CHO
Common system IUPAC system
Acrolein Prop-2-enal
Valeraldehyde Pentanal
Phthaldehyde Benzene-1,2-dicarbaldehyde
– C –
||
O
| |
CH3 – CH CH – CH3
CH3 CH3
CH3 – C – CH3
||
O
– C –
||
O
||
O
CH3 – CH2
CH2 – C – H
CH3 – C – CH2 – CH2 – CH3
||
O
||
O
OCH3
Common system IUPAC systemKetones
Acetone Propanone
Methyl n – propyl ketone Pentan – 2 – one
Di isopropyl ketone 2,4 – dimethylpentan – 3 – one
12345
3 – oxopentanal
12345
2 – methoxycyclohexanoneb – methoxycyclohexanone
a b
________
Lone pair of electrons
p
p
Lone pair of electrons
s
Unhybridised p orbital of oxygenUnhybridised p orbital of carbon
These two sp2 hybridised orbitals
of carbon available for formation
of s bond
Structure of functional group
C O
p
p
s
s
s Hybridisation of carbonyl ‘C’ – sp2
Hybridisation of ‘O’ – sp2
s
p
OC
120o
120o
120o
C O
s
p
p
General Methods of Preparation :
For both Aldehydes and Ketones :
Oxidation of primary alcohols gives aldehyde and oxidation of secondary alcohols gives Ketones. Here, (K2Cr2O7 / H2SO4) is a
strong oxidising agent.
1. By Oxidation of Alcohols :
By K2Cr2O7 / H2SO4 :
[O]
K2Cr2O7 / H2SO4 (dil)
R – C – H
||
O
Aldehyde1o alcohol
R – CH2 – OH
CH – OH
R
R’
2o alcohol
O
K2Cr2O7 / H2SO4 (conc.)
C = O
R
R’
Ketone
Aldehydes are quite susceptible to further oxidation to acids -
R – CH2 – OH
[O]
R – C – H
||
O
[O]
R – C – OH
||
O
Thus oxidation of primary alcohols is made at the temperature much above the boiling point of aldehyde and thus aldehydes
are vapourised out and prevented from being oxidised.
1° alcohol Aldehydes
2° alcohol ketones
PCC (Pyridinium chloro chromate) in CH2Cl2
PDC (Pyridinium di chromate) in CH2Cl2
Jones reagent (CrO3+H2SO4) in acetone
IMPORTANT
Mild Oxidising Agent:
1o alcohols will get oxidised with CrO3/Pyridine, Collin's reagent Ag/O2 at 250oC
Selective oxidising agents
When the vapours of a primary or a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an
aldehyde or a ketone is formed while tertiary alcohols undergo dehydration.
2. Dehydrogenation reaction
CH3 – CH2 – OH
Cu
573K
CH3 – CHO
CH – OH
CH3
CH3
Cu
573K
C = O
CH3
CH3
This reaction is used to determine the position of double bond in alkene.
3. By Ozonolysis of alkenes :
R – CH = CH2
O3
R – C CH2
| |
O O
O
Ozonide
R – CHO + HCHO
CH = CH2
R
R’
O3
R – C CH2
| |
O O
O
R’
C = O
R
R’
+ HCHO
Branched alkenes Ketones
Unbranched alkenes Aldehydes
Zn dust
H2O
Zn dust
H2O
(a) Hydration : With dil H2SO4 & 1% HgSO4 at 60 – 80oC.
4. From Alkyne:
CH ≡ CH + H2O CH2 = C – H
|
O – H
H2SO4 & 1% HgSO4
Enol form
CH3 – C – H
||
O
Keto form
Keto – enol tautomerism
CH3 – C ≡ CH + H2O
H2SO4 & 1% HgSO4
CH2 = C – CH3
|
O – H
CH3 – C – CH3
||
O
Acetylene Aldehydes
Other alkynes Ketones
Preparation of Aldehydes (specifically)
Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund
reduction.
Cl
O
C
||
H2
Pd – BaSO4
O
C – H
||
Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis
give corresponding aldehyde. This reaction is called Stephen reaction.
R – C ≡ N + SnCl2 + HCl
Cyanide stannous chloride
R – CH = NH
H3O +
R – CHO
Immine
1. From acyl chloride (acid chloride)
2. From nitriles and esters
HCHO cannot be prepared by this reaction
Alternatively, nitriles are selectively reduced by Di-isoButylaluminium hydride, (DIBAL – H) to imines followed by hydrolysis
to aldehydes:
R – CN
1. DIBAL – H
2. H2O
R – CHO
If double bond is present then that double bond is not reduced by DIBAL – H
CH3 – CH2 – CH = CH – CN
1. DIBAL – H
2. H2O
CH3 – CH2 – CH = CH – CHO
Similarly, esters are also reduced to aldehydes with DIBAL-H.
CH3– C – O – C2H5
||
O
1. DIBAL – H
2. H2O
CH3 – CHO + C2H5OH
Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons
3. From hydrocarbons
Strong oxidising agents oxidise toluene and its derivatives to benzoic acids.
As aldehyde group can undergo oxidation easily, methyl group attached to benzene ring first get converted to intermediate that is
difficult to oxidise and then finally it is converted to aldehydic group.
(i) By oxidation of methylbenzene (toulene)
CS2 H3O +
CH3
+ CrO2Cl2
Toulene
CH(OCrOHCl2)2
Chromium complex
H
O
C
||
Benzaldehyde
(a) Use of chromyl chloride (CrO2Cl2):
Chromyl chloride oxidises methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde. This is known
as Etard reaction.
(b) Use of chromic oxide (CrO3):
Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The
benzylidene diacetate can be hydrolysed to corresponding benzaldehyde
Toulene
CH3
+ CrO3 +
CH3 – C – O
O
CH3 – C – O
H3O +
D
CHO
CH
Benzylidene diacetate
O – C – CH3
||
O
O – C – CH3
||
O
CH
Benzylidene diacetate
O – C – CH3
||
O
O – C – CH3
||
O
Side chain chlorination of toluene gives Benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method
of manufacture of benzaldehyde.
(ii) By side chain chlorination followed by hydrolysis
CH3
Toulene
Cl2 / hn
CHCl2
Benzal chloride
H2O
373 K
CHO
When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium
chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde.
(iii) By Gatterman – Koch reaction
CO / HCl
Anhyd. AlCl3 / CuCl2
CHO
Preparation of ketones
1. From acyl chlorides
Treatment of acyl chlorides with dialkylcadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives
ketones.
+ CdCl2 R2Cd + 2 Mg
Cl
X
+ R2Cd + CdCl2
2 R’ – C – Cl
||
O
Acyl chloride
R – Mg – X
Grignard’s reagent
2 R’ – C – R
||
O
Ketone
Treating a nitrile (cyanide) with Grignard reagent followed by hydrolysis yields a ketone.
2. From nitriles
CH3 – CH2 – C ≡ N + C6H5MgBr
Anhyd. AlCl3
CS2
CH3 – CH2 – C
N – Mg – Br
C6H5
H3O+
CH3 – CH2 – C
O
C6H5
When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminium chloride, it gives the
corresponding ketone. This reaction is known as Friedel-Crafts acylation reaction.
3. From benzene or substituted benzenes
+ R – C – Cl
||
O
C
||
– R
O
Dry ether
4. From dry distillation of acids
Ca(OH)2
Dry distillationR – C – OH
||
O
R – C – R
||
O
DO IT YOURSELF…..
+ C2H5 – C – Cl
||
O1.
Anhyd. AlCl3
CS2
?
2. (C6H5CH2)2Cd + 2CH3COCl ?
3. CH3 – C ≡ C – H
Hg+, H2SO4
?
4. CH3
NO2
1. CrO2Cl
2. H3O+
?
Physical Properties
1. Physical states
Methanal is a gas at room temperature.
Ethanal is a volatile liquid.
Other aldehydes and ketones are liquid or solid at room temperature.
2. Boiling points
The boiling points of aldehydes and ketones are higher than hydrocarbons and ethers of comparable molecular masses. It is
due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling
points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding.
d+ d-
C = O
d+ d-
C = O
Dipole – dipole interaction
3. Solubility
The lower members of aldehydes and ketones such as methanal, ethanal and propanone are miscible with water in all
proportions, because they form hydrogen bond with water.
C = O
d+ d-
H – O
H
d+ d-
d+
d-
d+
However, the solubility of aldehydes and ketones decreases rapidly on increasing the length of alkyl chain. All aldehydes and
ketones are fairly soluble in organic solvents like benzene, ether, methanol, chloroform, etc.
The lower aldehydes have sharp pungent odours. As the size of the molecule increases, the odour becomes less pungent
and more fragrant. In fact, many naturally occurring aldehydes and ketones are used in the blending of perfumes and flavouring
agents.
4. Odour
Chemical Reactions the aldehydes and ketones undergo nucleophilic addition reactions.
(i) Mechanism of nucleophilic addition reactions
C O
d+ d-
sp2
Planar
C
O
_
Nusp3
Tetrahedral
Nu
_
C
O
_
Nu
Slow step
H+
Fast step
C
OH
Nu
Aldehydes are generally more reactive than ketones in nucleophilic addition reactions
(ii) Reactivity
Because ketones have two alkyl groups
That’s why more stearic hindrance is present
In ketone.
Ketones show lesser reactivity because
+I effect increases electron density on
carbonyl carbon. So partial positive charge
on carbon decreases
R C R
O Due to this partial positive charge
on this ‘C’ decreases
+ I + I
|
C
OH
|
C
OH
||
C
OH
+
–
||
C
OH
+
–
||
C
OH
+
–
||
C
OH
–
+
Aromatic aldehydes
Positive charge get developed on ortho and para position due to decrease in electron density on these positions.
Because of – M or – R effect of carbonyl group as it is EWG.
But lesser reactivity towards nucleophilic reactions than aliphatic aldehydes
In general,
Aliphatic Aldehydes > Aromatic aldehydes > Aliphatic Ketone > Aromatic ketone
Reactivity toward nucleophilic reactions decreases
Some important examples of nucleophilic addition and nucleophilic addition-elimination reactions
(a) Addition of hydrogen cyanide (HCN):
Aldehydes and ketones react with hydrogen cyanide (HCN) to yield cyanohydrins.
Cyanide and hydroxyl both groups
This reaction occurs very slowly with pure HCN. Therefore, it is catalysed by a base and the generated cyanide ion (CN-)
Mechanism
HCN
Base
+ OH
–
CN
–
+ H3O +
C = O CN
–
+ C
O
CN
–
C
O
CN
–
H
+
+ C
OH
CN
Tetrahedral complex
Cyanohydrin
C = O NaHSO3+ C
O Na
SO3H
– +
(b) Addition of sodiumhydrogensulphite:
Proton transfer
C
OH
SO3Na
The hydrogensulphite addition compound is water soluble and can be converted back to the original carbonyl compound by
treating it with dilute mineral acid or alkali. Therefore, these are useful for separation and purification of aldehydes.
Hydrogensulphite addition compound
(Crystalline)
Aldehydes react with one molecule of monohydric alcohol in the presence of dry hydrogen chloride to yield alkoxyalcohol
intermediate, known as hemiacetals, which further react with one more molecule of alcohol to give a gem – dialkoxy compound
known as acetal
(c) Addition of alcohols:
C = O
R
H
R’OH
HCl gas
C
R
H OH
O R’
Hemiacetal
C
R
H O R’
O R’
Hemiacetal
Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals.
C = O
R
R
CH2 – OH
+ |
CH2 – OH
HCl gas R
R
C
O
O
– CH2
– CH2
+ H2O
ethylene glycol ketal
(d) Addition of ammonia and its derivatives:
C = O C = NH H2O+C
OH
N – H
H
|
N – H+
|
H
|
H
C = O H2 N – R+ C = N – R Substituted imine (Schiff’s base)
C = O H2 N – H+ C = N – H Imine
1o amine
C = O H2 N – OH+
Hydroxyl amine
C = N – OH Oxime
C = O H2 N – NH2+
Hydrazine
C = N – NH2 Hydrazone
H2 N –+C = O
– H2O
– H2O
– H2O
– H2O
– H2O
C = N– Phenyl hydrazone
Phenyl hydrazine
C = O H2 N – NH –+ – NO2
O2N
– H2O
C = N – NH – – NO2
O2N
C = O H2 N – NH – C – NH2+
||
O
– H2O
C = N – NH – C – NH2
||
O
2,4-DNP-derivatives are yellow, orange or red solids, useful for characterisation of aldehydes and ketones.
Aldehydes and ketones are reduced to primary and secondary alcohols
respectively by sodium borohydride (NaBH4) or lithium aluminium hydride
(LiAlH4) as well as by catalytic hydrogenation
2. Reduction
LiAlH4 / THF or Ether
R – CH2 – OH
Primary alcohols
C = O
H
Aldehydes
R
C = O
R’
Ketones
R NaBH4 / THF or Ether
CH – OH
R’
Secondary alcohols
R
H2 / Pt
H2 / Pd
H2 / Ni
(i) Reduction to alcohols:
LiAlH4 NaBH4
Strong reducing agent Weak reducing agent
THF or ether used as
solvent
Aldehydes
Ketones
Carboxylic acids
Acid chlorides
Nitriles
Esters
Nitro compounds
THF or ether used as
solvent
Aldehydes
Ketones
Acid chlorides
Conjugate double
bond gets reduced
Conjugate double
bond does not get
reduced
Isolated double bond
does not get reduced
Isolated double bond
does not get reduced
The carbonyl group of aldehydes and ketones is reduced to CH2 group in these reactions.
(ii) Reduction to hydrocarbons:
Reduction to hydrocarbons
Clemmensen reduction
Carbonyl group is reduced to CH2 group on treatment with zinc amalgam and concentrated
hydrochloric acid
C = O
HCl
Zn – Hg
CH2
Wolff – Kishner reduction
C = O
– H2O
NH2 NH2
C = N – NH2
Heat
KOH / Ethylene glycol
CH2
C = O
420 K
Red P
CH2
3. Oxidation Aldehydes differ from ketones in their oxidation reactions.
Aldehydes Ketones
Easily oxidised to carboxylic acids on treatment with common
oxidising agents (strong or mild)
Cannot be oxidise easily and vigorous oxidation is required
Oxidation occurs at room temperature Oxidation occurs at high temperature
Cleavage of C – C bond does not take place Cleavage of C – C bond takes place
Oxidising agents
Strong Mild
Nitric acid Tollen’s reagent
Potassium permanganate Fehling’s solution
Potassium dichromate
Only strong oxidising agents are required.
Only one carboxylic acid gets formed
Mixture of carboxylic acids (having lesser carbon in each
than the parent ketone) gets formed
Aldehydes Ketones
C = O
H
Aldehydes
R [O]
R – COOH
CH3 – CH2 – CHO
[O]
CH3 – CH2 – COOH
CH3 – CH2 – C – CH2 – CH2 – CH3
||
O
[O]
CH3 – COOH + HOOC – CH2 – CH2 – CH3
CH3 – CH2 – C – CH2 – CH2 – CH3
||
O
[O]
CH3 – CH2 – COOH + CH3 – CH2 – COOH
DISTINGUISHING TESTS BETWEEN ALDEHYDES AND KETONES
1. Tollens test (Oxidation by Tollen’s reagent)
Bernhard Tollens (1841-1918) was a Professor of Chemistry at the University of Gottingen, Germany.
Tollen’s reagent is ammoniacal AgNO3 solution. When aldehydes are heated with Tollens reagent, aldehydes gets oxidised to
carboxylate ion and Tollens’ reagent gets reduced into bright silver mirror.
2 AgNO3 + 2NH4OH Ag2O + 2NH4NO3 + H2O
Ag2O + 4NH4OH 2 [ Ag (NH3)2] OH + 3H2O
–+
RCHO + 2 [ Ag (NH3)2] + 3 OH RCOO + 2Ag ↓ + 2H2O + 4 NH3
+ – –
silver mirror
Only aldehydes show this test positive. Ketones do not show this test positive.
2. Fehling’s test (Oxidation by Fehling’s reagent)
Fehling A – Aqueous CuSO4 Fehling B – Alkaline sodium potassium tartarate (Rochelle salt)
These two solutions are mixed in equal amounts. On heating aldehyde with this solution a reddish brown precipitate of Cu2O
is formed and aldehyde is oxidised to corresponding carboxylate anion.
RCHO + 2 Cu + 5 OH RCOO + Cu2O ↓ + 3H2O
2+ – –
reddish brown ppt
Aromatic aldehydes do not show this test
3. Haloform test
Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidised by
sodium hypohalite (Cl2, Br2 or I2 in presence of NaOH) to give sodium salts of corresponding carboxylic acids having one carbon
atom less than that of carbonyl compound.
The methyl group is converted to haloform. (Chloroform, bromoform or iodoform)
This oxidation does not affect a carbon-carbon double bond, if present in the molecule.
CH3 – C –
||
O
CH3 – CH –
|
OH
Then only this test is positive
(Exception – Ethanol)
R – C – CH3
||
O
NaOX
R – C – O Na
||
O
– +
+ CH3 – X
Haloform
X = Cl, Br, I
COMMON EXAMPLES OF HALOFORM TEST
Remember only CH3 – C –
||
O
CH3 – CH –
|
OH
and show this test positive. Only exception is ethanol
1. Ethanol and methanol
CH3 – CH2 – OH
Ethanol
CH3 – OH
Methanol
Positive Negative
2. Acetaldehyde and formaldehyde
CH3 – C – H
||
O
H– C – H
||
O
Positive Negative
3. Acetaldehyde and benzaldehyde
CHO
CH3 – C – H
||
O
Positive Negative
4. Acetophenone and benzaldehyde
CHOC – CH3
O
Positive Negative
5. Acetone and propanal
CH3 – C – CH3
||
O
CH3 – CH2– C – H
||
O
Positive Negative
6. pentan-2-one and pentan-3-one
7. Isopropyl alcohol and n – propyl alcohol
CH3 – CH2– CH2 – C – CH3
||
O
CH3 – CH2– C – CH2 – CH3
||
O
Positive
Negative
CH3 – CH – CH3
|
OH
CH3 – CH2 – CH2 – OH
Positive
Negative
SOME IMPORTANT PROBLEMS
Problem 1 How can you perform following conversions?
(a) But-2-ene to ethanal
CH3 – CH = CH – CH3
1. O3
2. Zn/H2O
2 CH3 – CHO
(b) Cyclohexanol to cyclohexanone
|
OH
K2Cr2O7 / H2SO4
||
O
Here you can use mild oxidising agents like
1. PCC in CH2Cl2
2. PDC in CH2Cl2
3. Jones reagent (CrO3+H2SO4) in acetone
4. CrO3/Pyridine
5. Collin's reagent Ag/O2 at 250oC
(c) Butyne to Butan-2-one
CH3 – CH2 – C ≡ CH
HgSO4 / H2SO4
CH3– CH2 – C – CH3
||
O
CHO
NO2
(d) p – nitrotoulene to p – nitrobenzaldehyde
CH3
NO2
1. CrO2Cl2 / CS2
2. H3O +
Here you can also use
1. chromic oxide (CrO3) with acetic anhydride followed by hydrolysis
2. Side chain chlorination followed by hydrolysis at 373 K
(Commercial method) (Benzal chloride formed as intermediate)
Etard reaction – Chromium complex is formed as intermediate
Problem 2 How can you perform following conversions?
(a) Propanone to propene
(b) Propanal to butanone
(c) Benzaldehyde to benzophenone
CH3 – C – CH3
||
O
LiAlH4
CH3 – CH – CH3
|
OH
H2SO4
CH3 – CH = CH2
CH3 – CH2– C – H
||
O
+ CH3 MgBr
Dry ether
CH3 – CH2– C – H
|
O Mg Br
|
CH3
CH3 – CH2– CH
|
OH
|
CH3
Mg
Br
OH
+
CH3 – CH2– CH – CH3
|
OH
K2Cr2O7 / H2SO4
CH3 – CH2 – C – CH3
||
O
CHO
KMnO4 / OH -
COOH
Ca(OH)2
Dry distillation
C
||
O
H3O +
Problem 3 Complete the following reactions
(d) Benzaldehyde to a hydroxyphenylacetic acid
HCN / OH -
C – CN
OH
H –
C
O
H –
H3O +
C – COOH
OH
H –
Alc. KOH
D
A
1. O3
2. Zn / H2O
B + C
Alc. KOH
D
O3
+CH3 – C– CH2 – CH3
|
CH3
|
Cl
CH3 – C CH – CH3
| |
O O
O
CH3
Zn / H2O
CH3 – C – CH3
||
O
B
CH3 – C – H
||
O
C
CH3 – C = CH – CH3
|
CH3
A
CH3 – C– CH2 – CH3
|
CH3
|
Cl
(a)
Alc. KCN
A
1. SnCl2 / HCl
2. H3O+
B
CH3 – CH – CH3
|
I
Alc. KCN 1. SnCl2 / HCl
2. H3O+
CH3 – CH – CH3
|
CN
A
CH3 – CH – CH3
|
CHO
B
1. CrO2Cl2 / CS2
2. H3O +
CH3
CH3
1. CrO2Cl2 / CS2
2. H3O +
A
CHO
CHO
A
CH3 – CH – CH3
|
I
(b)
CH3
CH3
(c)
+ H2
Pd / BaSO4
(CH3)2CH – CHO
(CH3)2CH – CHOCH3 – CH – C – Cl
||
O
|
CH3
(d)
A + H2
Pd / BaSO4
+ NaOI A + BCH3 – C – C – CH3
||
O
|
CH3
|
CH3
(e)
CH3 – C – C – CH3
||
O
|
CH3
|
CH3
+ NaOI CH3 – C – C – O Na
||
O
|
CH3
|
CH3
– +
A
+ CHI3
B
NH2NHCONH2
A
CHO
NH2NHCONH2
CH = N – NHCONH2
A
CHO
(f)
||
O
|
CHO
||
O
|
COO
–
A
||
O
|
CHO
(g)
[ Ag (NH3)2] OH
–+
[ Ag (NH3)2] OH
–+
REACTIONS DUE TO a HYDROGEN
Aldehydes or ketones having at least one a hydrogen show aldol condensation reaction in presence of dilute alkali [e.g.
NaOH, Na2CO3 or Ba(OH)2].
Aldol condensation
– C– C– C – C – C – C –
||
O
|
|
H
H
|
|
H
H
H – C – H
||
O
a a'a
CHO
– C– C– C – C – H
||
O
|
|
H
H
Two molecules of same aldehydes or ketones with a hydrogen condense together (combine together) to form b – hydroxy
aldehyde or b – hydroxy ketone which undergo dehydration to form a , b unsaturated aldehydes or ketones.
–– C –– C ––
||
O
|
H
This a hydrogen becomes acidic because electron density around this hydrogen
decrease due to – I effect of carbonyl carbon. So it can be easily given out as H + in
solution if we use base which can extract this proton
carbonyl group is EWG and shows – I effect.
(a) Simple aldol or self aldol condensation
After the removal of H+ the carbanion formed is stable due to resonance.
–– C –– C ––
||
O
|
H
B
–– C –– C ––
||
O
–
carbanion
+ BH
–– C –– C ––
||
O
–
–– C = C ––
|
O
–
CH3 – C
||
O
|
H
H – CH2 – C – H
||
O
CH2 – C – CH2 – C – H
|
OH O
||
|
H
ab
b – hydroxy aldehyde (aldol)
ab ab
a , b – unsaturated aldehyde
–H2O
D
OH
–
CH2 – CH – CH – C – H
|
OH O
|||
H
CH2 – CH = CH – C – H
O
||
Mechanism
CH3 – C
||
O
|
CH3
H – CH2 – C – CH3
||
O
OH
–
CH3 – C – CH2 – C – CH3
|
OH O
||
|
CH3
CH3 – C – CH – C – CH3
|
OH O
||
|
CH3
|
H
–H2O
D
CH3 – C = CH – C – CH3
O
||
|
CH3
b – hydroxy ketone (ketol)
ab
ab
a , b – unsaturated ketone
CH3 – C – CH3
||
O
CH3 – CH2– C – H
||
O
+
(b) Crossed aldol condensation
Simple aldol or self aldol products
CH3 – C – CH3
||
O
CH3 – C – CH3
||
O
+
OH
–
CH3 – C – CH2 – C – CH3
|
OH O
||
|
CH3
–H2O
D
CH3 – C = CH – C – CH3
O
||
|
CH3
Four products are possible
CH3 – CH2– C – H
||
O
CH3 – CH2– C – H
||
O
+ CH3 – CH2– C – CH – C – H
|
OH
|
H
||
CH3
|
O
OH
–
–H2O
D
CH3 – CH2– C = C – C – H
|
H
||
CH3
|
O
CH3 – CH2– C – H
||
O
OH
–
CH3 – CH2– C – CH2 – C – CH3
|
OH
|
H
||
O
CH3 – C – CH3
||
O
+
–H2O
D
CH3 – CH2– C = CH – C – CH3
|
H
||
O
Crossed aldol products
CH3 – C – CH3
||
O
CH3 – CH2– C – H
||
O
+ CH3 – C – CH – C – H
|
OH O
||
|
H3C
|
CH3
OH
–
–H2O
D
CH3 – C = C – C – H
O
||
|
H3C
|
CH3
In case of crossed aldol condensation, any one aldehyde or ketone has a hydrogen and other does not have a carbon then also
reaction is possible as given below.
CHO
CH3 – C – CH3
||
O
+
OH
–
CH – CH2 – C – CH3
|||
OH O
–H2O
D
CH = CH – C – CH3
||
O
Cannizzaro reaction
Aldehydes which do not have any a H atom such as HCHO, C6H5CHO undergo self oxidation and self reduction on treatment with
conc. Alkali. In this, one molecule is reduced to alcohol and another molecule gets oxidised into salt of carboxylic acid.
HCHO + HCHO
Conc. KOH
CH3OH + HCOOK
CHO CHO
+
Conc. NaOH
CH2OH COONa
+
Self Cannizzaro reaction
Crossed Cannizzaro reaction
+ HCHO
CHO
Conc. NaOH
CH2OH
+ HCOONa
In case of crossed Cannizzaro of any aldehyde and formaldehyde always oxidation of formaldehyde takes place i.e. always salt
of formic acid gets formed
Electrophilic substitution reactions (aromatic aldehydes and ketones)
In case of aromatic aldehydes and ketones, they undergo electrophilic substitution reaction at meta position because – CHO is
EWG and shows – R effect. As all EWG are meta directing, so substitution occurs at meta position. (Electron density decreases
on ortho and para position so, positive charge gets developed.)
|
C
OH
|
C
OH
||
C
OH
+
–
||
C
OH
+
–
||
C
OH
+
–
||
C
OH
–
+
(a) Halogenation
CHO
+ Cl2
FeCl3
CHO
Cl
+ HCl
COCH3
+ Cl2
FeCl3
COCH3
Cl
+ HCl
(b) Nitration
CHO
Conc. HNO3 + Conc.H2SO4
Nitrating mixture
CHO
NO2
(c) Sulphonation
CHO
Fuming H2SO4
CHO
SO3H
COCH3
Fuming H2SO4
COCH3
SO3H
USES OF ALDEHYDES AND KETONES
1. 40% HCHO is known as formalin used in preservation of biological specimens
2. Formaldehyde is also used as disinfectant
3. Acetaldehyde is sued for silvering mirrors
4. Benzaldehyde is used in perfume industry
6. Many aldehydes and ketones like vaniline (used as vanilla flavour), cinnamaldehyde (used as cinnamon flavour) used for flavour
5. Acetone is used as solvent in industries as well as paints
CARBOXYLIC ACIDS
Large number of carboxylic acids are found in nature. Some higher members of aliphatic carboxylic acids (C12 – C18) known as
fatty acids.
Carbon compounds containing a carboxyl functional group, –COOH are called as carboxylic acids.
The carboxyl group, consists of a carbonyl group attached to a hydroxyl group, hence its name carboxyl.
Carboxylic acids
Aliphatic (RCOOH)
Aromatic (ArCOOH)
Alkyl group attached to – COOH group
Aromatic ring attached to – COOH group
NOMENCLATURE AND STRUCTURE OF CARBOXYL GROUP
Common system
Large number of carboxylic acids are known by their common names because many of the are naturally occurring.
The common names end with the suffix –ic acid and have been derived from Latin or Greek names of their natural sources.
For example
Formic acid HCOOH First obtained from red ants (Latin: formica means ant)
Acetic acid CH3COOH First obtained from vinegar (Latin: acetum, means vinegar)
Butyric acid CH3CH2CH2COOH First obtained from rancid butter (Latin: butyrum, means butter)
IUPAC system
Aliphatic carboxylic acids are named by replacing the ending –e in the name of the corresponding alkane with – oic acid.
Presence of one –COOH group – oic acid
Presence of two –COOH group dicarboxylic acid
Presence of three –COOH group tricarboxylic acid
Remember priority series
1. f any other functional group present along with – COOH
group then that group gets lesser priority and can be used as
prefix of that group.
2. Only sulphonic acid has higher priority than that of –
COOH group and can be used as suffix.
Common nameCompound IUPAC name
CH3COOH
CH3CH2COOH
CH3 – CH – CH – CH2 – COOH
|
OH
12345
Acetic acid Ethanoic acid
Propionic acid Propanoic acid
Isobutyric acid 2 – methyl propanoic acidCH3 – CH – COOH
|
CH3
23 1
CH3 – CH – CH2 – CH2 – CH2 – COOH
|
Cl
23456 1
5 – chloro hexanoic acid______
5 – chloro hexanoic acidCH3 – CH = CH – CH2 – CH2 – COOH
23456 1
______
______
3 – hydroxy pentanoic acid
Common nameCompound IUPAC name
COOH
|
CH3
COOH
2
1
COOH
COOH
1
2
2 – methyl cyclopentane carboxylic acid
CH2 – CH2 – COOH
23 1
______
3 – phenyl propanoic acid______
______
Benzoic acid
Phthalic acid Benzene –1–2–dicarboxylic acid
Common nameCompound IUPAC name
Salicylic acid
Anisic acid
COOH
OH
1
2
COOH
OCH3
1
2
3
4
Dibasic acids
COOH
COOH
|
COOH
COOH
|
CH2
|
2 – hydroxy benzoic acid
4 – methoxy benzoic acid
Oxalic acid
Malonic acid
Ethanedioic acid
Propanedioic acid
COOH
CH2
|
CH2
|
CH2
|
COOH
|
COOH
CH2
|
CH2
|
COOH
|
Succinic acid
Common nameCompound IUPAC name
Butanedioic acid
Glutaric acid Hexanedioic acid
STRUCTURE OF CARBOXYL GROUP
C
O H
O
sp2 hybridisation
sp3 hybridisation
sp2 hybridisation
120o
C
O H
O
Resonance structures:
C
O H
O
-
+ C
O H
O
-
+
METHODS OF PREPARATION OF CARBOXYLIC ACIDS
1. From primary alcohols and aldehydes (by oxidation)
Primary alcohols
Oxidising agents
Aldehydes
1. KMnO4 in alkaline medium [KMnO4 / OH -]
Followed by hydrolysis
2. KMnO4 in acidic medium [KMnO4 / H+]
3. K2Cr2O7 in acidic medium [K2Cr2O7 / H+]
1. CrO3
2. Pyridinium chloro chromate (PCC)
3. Pyridinium dichromate (PDC)
4. Jones reagent (CrO3+H2SO4) in acetone
CH3 – CH2 – CH2 – OH
1. KMnO4 / OH -
2. H3O+
CH3 – CH2 – COOH
CH3 – CH – CH2 – CHO
CH3
|
PCC
CH3 – CH – CH2 – COOH
CH3
|
Primary and secondary alkyl groups are oxidised in this manner while tertiary group is not affected.
2. From alkylbenzenes
Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline
potassium permanganate.
The entire side chain is oxidised to the carboxyl group irrespective of length of the side chain.
CH3
KMnO4 – KOH
Heat
COO K
– +
H3O+
COOH
CH2 – CH2 – CH3
KMnO4 – KOH
Heat
COO K
– +
H3O+
COOH
Nitriles are hydrolysed to amides and then to acids in the presence of H+ or OH– as catalyst.
3. From nitriles and amides
R – CN
H + or OH–
H2O
R – C – NH2
||
O
H + or OH–
D
R – C – OH
||
O
CONH2
H + or OH–
D
COOH
Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which in turn give corresponding carboxylic
acids after acidification with mineral acid.
4. From Grignard reagents
R Mg X + O = C = O
Dry ether
R– C
O
O Mg
_ +
H3O+
R – C – OH
||
O
Mg
X
OH
+
Anhydrides are hydrolysed to corresponding acid(s) with water.
5. From acyl halides and anhydrides
Acid chlorides when hydrolysed with water give carboxylic acids or more readily hydrolysed with aqueous base to give carboxylate
ions which on acidification provide corresponding carboxylic acids.
C6H5 – C
O
C6H5 – C
O
O
||
||
R – C – Cl
||
O
H2O
OH / H2O
_
R – C – O
||
O
_
+ Cl
_ H3O+
R – C – OH
||
O
+ HCl
R – C – OH
||
O
H2O
2 C6H5– C – OH
||
O C6H5 – C
O
C2H5 – C
O
O
||
||
H2O
C6H5– C – OH
||
O
C2H5– C – OH
||
O
+
6. From esters
COOC2H5 COOH
+ C2H5OH
H3O+
PHYSICAL PROPERTIES
Aliphatic carboxylic acids up to nine carbon atoms are colourless liquids at room temperature with unpleasant odours.
The higher acids are wax like solids and are practically odourless due to their low volatility.
1. Physical states
2. Boiling point
R C
O
OH
d –
d+
C R
O
OHd+
d –
Intermolecular H – bonding
Carboxylic acids have highest boiling point among all functional groups in organic compounds.
3. Solubility
R C
O
OH
d –
d+
H – O
H
d+ d-
d+
H – O
H
d+
d-
d+
Benzoic acid, the simplest aromatic carboxylic acid is nearly insoluble in cold water.
Simple aliphatic carboxylic acids having upto four carbon atoms are miscible in water due to the formation of hydrogen
bonds with water.
The solubility decreases with increasing number of carbon atoms. Higher carboxylic acids are practically insoluble in
water due to the increased hydrophobic interaction of hydrocarbon part.
Carboxylic acids are also soluble in less polar organic solvents like benzene, ether, alcohol, chloroform, etc.
CHEMICAL REACTIONS OF CARBOXYLIC ACIDS
Acidity of carboxylic acids
Carboxylic acids react with active metals like sodium, potassium etc. to give hydrogen gas
2 R – C – OH + 2 Na
||
O
R – C – O Na
||
O
_ +
+ H22
Carboxylic acids react with alkalis to form salt and water (neutralisation reaction)
R – C – OH + NaOH
||
O
R – C – O Na
||
O
_ +
+ H2O
Carboxylic acids react with weaker bases like sodium carbonate, sodium bicarbonate etc. to form salt and carbon
dioxide is evolved
R – C – OH + NaHCO3
||
O
R – C – O Na
||
O
_ +
+ H2O + CO2
Carboxylic acids dissociate in water to give resonance stabilised carboxylate anions and hydronium ion.
R – C – OH + H2O
||
O
R – C – O
||
O
_
+ H3O +
R C
O
O
_ R C
O
O
_
R C
O
O
-
Carboxylate ion
Resonance structures of carboxylate ion
Resonance hybrid
Now, consider the same reaction,
R – C – OH + H2O
||
O
R – C – O
||
O
_
+ H3O +
Equilibrium constant for this reaction can be given as,
K =
[RCOO ] . [H3O+]
_
[RCOOH] . [H2O]
∴ K [H2O] =
[RCOO ] . [H3O+]
_
[RCOOH]
∴ Ka=
[RCOO ] . [H3O+]
_
[RCOOH]
pKa = – log10 Ka
Remember
Higher Ka Value stronger is the acid
Higher pKa value weaker is the acid
For strong acid pKa < 1
For moderately strong acid 5 > pKa > 1
For weak acid 15 > pKa > 5
For extremely weak acids pKa > 15
EFFECT OF SUBSTITUENTS ON THE ACIDITY OF CARBOXYLIC ACIDS
If EWG group is attached to R chain in – COOH group then acidity of carboxylic acid increases
EWG C
O
O
-
– I
Case 1:Acidity of carboxylic acid depends upon which EWG group is attached to – COOH
Increase in acidity of acid is in order.
Ph < I < Br < Cl < F < CN < NO2 < CF3
e.g. Arrange the following acids in increasing order of acidic strength
CH3 – CH2 – CH – CH2 – COOH
|
NO2
(I)
CH3 – CH2 – CH – CH2 – COOH
|
I
(II)
CH3 – CH2 – CH – CH2 – COOH
|
F
(III)
CH3 – CH2 – CH – CH2 – COOH
|
(IV)
Case 2: Acidity of carboxylic acid depends upon no. of EWG attached to carbon chain
No. of EWG increases acidity of acid also increases
e.g. Arrange the following acids into their increasing order of acidic strength
F – C – CH2 – COOH
F
|
F
|
(I)
CH2 – CH2 – COOH
|
F
(II)
CH – CH2 – COOH
|
F
|
F
(III)
CH3 – CH2 – COOH
(IV)
Case 3: Acidity of carboxylic acid depends upon position of EWG in carbon chain.
CH3 – CH2 – CH2 – CH – COOH
|
CN
(I)
CH3 – CH – CH2 – CH2 – COOH
CN
|
(II)
CH2 – CH2 – CH2 – CH2 – COOH
CN
|
(III)
CH3 – CH2 – CH – CH2 – COOH
CN
|
(IV)
e.g. Arrange the following acids into their increasing order of acidic strength
If EDG group is attached to R chain in – COOH group then acidity of carboxylic acid decreases
EDG C
O
O
-
+ I
e.g. groups like – R, – OR etc.
CH3 – C – CH2 – COOH
CH3
|
CH3
|
(I)
CH2 – CH2 – COOH
|
CH3
(II)
CH – CH2 – COOH
|
CH3
|
CH3
(III)
CH3 – CH2 – COOH
(IV)
e.g. Arrange the following acids into their increasing order of acidic strength
Same can be applied for aromatic acids as well.
1. Formation of anhydride
Carboxylic acids on heating with mineral acids such as H2SO4 or with P2O5 give corresponding anhydride
CH3 C
O
OH
+ C CH3
OH
O
H+
, D
Or P2O5 , D
CH3 C
O
C CH3
O
O
2. Esterification
R – OH + R’ COOH
H+
R COOR’ + H2O
3. Reactions with PCl5, PCl3 and SOCl2
R – C – OH + PCl5
||
O
R – C – Cl + POCl3 + HCl
||
O
3 R – C – OH + PCl3
||
O
3 R – C – Cl + H3PO3
||
O
The hydroxyl group of carboxylic acids, behaves like that of alcohols and is easily replaced by chlorine atom on treating
with PCl5, PCl3 or SOCl2.
R – C – OH + SOCl2
||
O
R – C – Cl + SO2 + HCl
||
O
Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature give amides.
4. Reaction with ammonia
CH3– C – OH + NH3
||
O
D
– H2O
COOH
COOH
+ NH3
D
– 2H2O
CH3 – C – O NH4
||
O
– +
Ammonium acetate
CH3– C – NH2
||
O
Acetamide
COO NH4
COO NH4
– +
– +
Ammonium phthalate
Strong heating
– NH3
Phthalamide
C – NH2
C – NH2
||
O
||
O
C
C
||
O
||
O
NH
Phthalimide
Carboxylic acids are reduced to primary alcohols by lithium aluminium hydride or better with diborane.
5. Reduction
Diborane reduces carboxylic acid and unsaturation selectively. Diborane does not reduce functional groups such as ester,
nitro, halo, etc.
RCOOH RCH2OH
1. LiAlH4
2. H3O+
RCOOH RCH2OH
B2H6
Carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with sodalime (NaOH and CaO in
the ratio of 3 : 1). The reaction is known as decarboxylation.
6. Decarboxylation
RCOONa
NaOH & CaO
Heat
RH + Na2CO3
Alkali metal salts of carboxylic acids also undergo decarboxylation on electrolysis of their aqueous solutions and form hydrocarbons
having twice the number of carbon atoms present in the alkyl group of the acid. The reaction is known as Kolbe electrolysis
Carboxylic acids having an α-hydrogen are halogenated at the a-position on treatment with chlorine or bromine in the presence
of small amount of red phosphorus to give a-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.
7. Halogenation
R – CH2 – COOH
1. X2 / Red phosphorus
2. H3O+
R – CH – COOH
|
X
(X = Cl, Br)
Aromatic carboxylic acids undergo electrophilic substitution reactions in which the carboxyl group acts as a deactivating and
meta-directing group. They however, do not undergo Friedel-Crafts reaction because the carboxyl group is deactivating and the
catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group.
8. Electrophilic substitution of aromatic acids
COOH
NO2
COOH
HNO3 + H2SO4
COOH
Br
COOH
Br2 / FeBr3
1. Hexanedioic acid is used in the manufacture of nylon-6, 6.
2. Esters of benzoic acid are used in perfumery.
3. Sodium benzoate is used as a food preservative.
4. Higher fatty acids are used for the manufacture of soaps and detergents.
USES OF CARBOXYLIC ACIDS
IMPORTANT
PROBLEMS FOR
BOARD EXAM
Q.1 Write the structures of products of the following reactions
O
+ HO – NH2
H+
O
H2 N – NH –+ – NO2
O2N
H2N – NH – C – NH2
||
O
R – CH = CH – CHO +
Q. 2. Write chemical reactions to affect the following transformations:
(i) Butan-1-ol to butanoic acid
(ii) Benzyl alcohol to phenylethanoic acid
(iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid
CH3 – CH2 – CH2 – CH2 – OH
[O]
CH3 – CH2 – CH2 – COOH
CH2 – OH
Mg
Ether
CH2 – Br CH2 – CN
KCN
CH2 – COOH
1. Reduction
2. H3O+ D
Br
NO2
Mg Br
NO2
Dry ice (CO2)
Dry Ether
C
NO2
O Mg BrO
C
NO2
OHO
HBr
H3O+
Mg
Br
OH
+
(vi) Butanal to butanoic acid.
(iv) 4-Methylacetophenone to benzene-1,4-dicarboxylic acid
(v) Cyclohexene to hexane-1,6-dioic acid
COCH3
CH3
KMnO4 / KOH
COOK
COOK
H3O+
COOH
COOH
benzene-1,4-dicarboxylic acid
Terephthalic acid
KMnO4 / H2SO4
Heat
COOH
COOH
CH3 – CH2 – CH2 – CHO
[O]
CH3 – CH2 – CH2 – COOH
Q. 3 Show how each of the following compounds can be converted to benzoic acid.
(i) Ethylbenzene
(ii) Acetophenone
(iii) Bromobenzene
C2H5
KMnO4 / KOH
COOK
H3O+
COOH
COCH3
1. KMnO4 / OH
_
2. Hydrolysis
COOH
+ CH3COOH
Br
Mg
Ether
Mg Br
Dry ice (CO2)
Dry Ether
C
O Mg BrO
C
OHO
H3O+
Mg
Br
OH
+
(iv) Phenylethene (Styrene)
CH = CH2
KMnO4 / KOH
COOK
H3O+
COOH
Q. 4 Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents.
(i) PhMgBr and then H3O+
(ii) Tollens’ reagent
C
O H
+ PhMgBr
Dry
Ether
CBr Mg O H
Ph
H3O+
CHO H
Ph
Mg
Br
OH
+
C
O H
Tollen’s reagent
Ammoniacal solution of AgNO3
C
O O
_
+ 2 Ag ↓ + 4NH3 + 2H2O
(iii) Semicarbazide and weak acid
C
O H
(iv) Excess ethanol and acid
H2N – NH – C – NH2
||
O
+
H+
C
O H
C2H5 – OH
C2H5 – OH
H+
C H
OC2H5
C2H5 O
+ H2O
(v) Zinc amalgam and dilute hydrochloric acid
C
O H
Zn – Hg / HCl
CH3
Q. 5. Which of the following compounds would undergo aldol condensation, which the Cannizzaro reaction and which neither?
Write the structures of the expected products of aldol condensation and Cannizzaro reaction.
(i) Methanal
(ii) 2-Methylpentanal
(iii) Benzaldehyde
(iv) Benzophenone
(viii) Butan-1-ol
(ix) 2,2-Dimethylbutanal
(v) Cyclohexanone
(vi) 1-Phenylpropanone
(vii) Phenylacetaldehyde
HOME WORK
Q. 6 How will you convert ethanal into the following compounds?
(ii) But-2-enal
(iii) But-2-enoic acid
(i) Butane-1,3-diol
CH3 – CHO
Dil. NaOH
Self aldol
CH3 – CH – CH2 – CHO
|
OH
CH3 – CH – CH2 – CH
|
OH
|
OH
D
– H2O
CH3 – CHO
Dil. NaOH
Self aldol
CH3 – CH – CH2 – CHO
|
OH
NaBH4
CH3 – CH = CH – CHO
D
– H2O
CH3 – CHO
Dil. NaOH
Self aldol
CH3 – CH – CH2 – CHO
|
OH
CH3 – CH = CH – CHO
Mild oxidising agent
CH3 – CH = CH – COOH
Q. 7. How will you bring about the following conversions in not more than two steps?
(i) Propanone to Propene
(ii) Benzoic acid to Benzaldehyde
(iii) Ethanol to 3-Hydroxybutanal
CH3 – C – CH3
||
O
CH3 – CH – CH3
|
OH
CH3 – CH = CH2
COOH
NaBH4 H2SO4
D
SOCl2
COCl CHO
Pd / BaSO4
H2
CH3 – CH2 – OH
[O]
CH3 – CHO CH2 – C – CH2 – C – H
|
OH O
||
|
H
Dil. NaOH
Self aldol
(iv) Benzene to m-Nitroacetophenone
(v) Benzaldehyde to Benzophenone
CH3COCl / Anhyd. AlCl3
Friedel – Craft acylation
C – CH3
||
O
HNO3 + H2SO4
C – CH3
||
O
NO2
(vi) Bromobenzene to 1-Phenylethanol
COOHCHO
[O] SOCl2
COCl
Anhyd. AlCl3
C
||
O
Br
Mg
Ether
Mg Br
1. CH3CHO
2. H2O
H3C – C – H
|
OH
Mg
Br
OH
+
(viii) Benzoic acid to m- Nitrobenzyl alcohol
(vii) Benazaldehyde to α-Hydroxyphenylacetic acid
CHO CH – CN
|
OH
CH – COOH
|
OH
NaCN / HCl H+ / HCl
COOH
HNO3 + H2SO4
COOH
NO2
B2H6
CH2OH
NO2
Xii aldehydes, ketones, carboxylic acid

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Xii aldehydes, ketones, carboxylic acid

  • 1. Aldehydes, ketones and carboxylic acids By – Mr. Pranav A. Galgale PGT Chemistry
  • 2. Organic Compounds having >C=O group are called carbonyl compounds. It's general formula is Cn H2nO (n = 1, 2, 3......) Carbonyl compounds are grouped into two categories. C = O H Aldehydes (also known as formyl group). It is a monovalent group (only one bond to get attached with carbon chain) Ketones C = O its both the valencies are satisfied by alkyl group. It is a bivalent group. – C – OH || O – C – NH2 || O – C – O – R || O – C – X || O – C = OH | O – + – C = NH2 | O – + – C = O – R | O – + – C = X | O – + – C – || O These groups contain but still they are not considered as carbonyl compounds as carbonyl group take part in resonance
  • 3. Nomenclature of aldehydes and ketones The common names of most aldehydes are derived from the common names of the corresponding carboxylic acids by replacing the ending –ic of acid with aldehyde. Names are given from name of source in Latin or in Greek e.g. Formaldehyde – Derived from formic acid present in ant sting (Greek: Forma – Ant) Propionaldehyde – Derived from propionic acid (Greek: Propion – Butter) Butyraldehyde – Derived from buyric acid (Greek: Butyr – Butter) The location of the substituent in the carbon chain is indicated by Greek letters a, b, g, d, etc. Nomenclature of aldehydes Common system
  • 4. Nomenclature of ketones The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group. The locations of substituents are indicated by Greek letters, a, a’, b, b’ and so on…. e.g. C – C – C – C – C || O a a’b b’ IUPAC names Aldehydes –e of alkanes replaced by –al In case of aldehyde group attached to cycloalkanes or benzene ring then word carbaldehyde is used as suffix in both the systems Ketones –e of alkanes replaced by –one Remember priority series: – SO3H used as suffix (sulphonic acid) – COOH used as suffix (–oic acid) Rest for all functional groups used as prefix If aldehyde and ketone both groups are there, then name aldehydic group is written in suffix (–al) and name of ketone is used as prefix (–oxo)
  • 5. CH3 – C – H || O – C – H || O CH3 – CH = CH – CH2 | CHO | CHO CH3 CHO NO2 12345 1 2 Common system IUPAC system Acetaldehyde Ethanal Cyclohexanecarbaldehyde Cyclohexanecarbaldehyde pent – 3 – enal 2 – methylcyclopentanecarbaldehyde o - nitrobenzaldehyde o - nitrobenzenecarbaldehyde 4 - nitrobenzaldehyde o - nitrobenzenecarbaldehyde ________ b – methylcyclopentanecarbaldehyde Aldehydes a b
  • 6. CH2 = CH – CHO CH3 – CH2 – CH2 – CH2 – CHO CHO CHO Common system IUPAC system Acrolein Prop-2-enal Valeraldehyde Pentanal Phthaldehyde Benzene-1,2-dicarbaldehyde
  • 7. – C – || O | | CH3 – CH CH – CH3 CH3 CH3 CH3 – C – CH3 || O – C – || O || O CH3 – CH2 CH2 – C – H CH3 – C – CH2 – CH2 – CH3 || O || O OCH3 Common system IUPAC systemKetones Acetone Propanone Methyl n – propyl ketone Pentan – 2 – one Di isopropyl ketone 2,4 – dimethylpentan – 3 – one 12345 3 – oxopentanal 12345 2 – methoxycyclohexanoneb – methoxycyclohexanone a b ________
  • 8. Lone pair of electrons p p Lone pair of electrons s Unhybridised p orbital of oxygenUnhybridised p orbital of carbon These two sp2 hybridised orbitals of carbon available for formation of s bond Structure of functional group
  • 9. C O p p s s s Hybridisation of carbonyl ‘C’ – sp2 Hybridisation of ‘O’ – sp2 s p OC 120o 120o 120o C O s p p
  • 10. General Methods of Preparation : For both Aldehydes and Ketones : Oxidation of primary alcohols gives aldehyde and oxidation of secondary alcohols gives Ketones. Here, (K2Cr2O7 / H2SO4) is a strong oxidising agent. 1. By Oxidation of Alcohols : By K2Cr2O7 / H2SO4 : [O] K2Cr2O7 / H2SO4 (dil) R – C – H || O Aldehyde1o alcohol R – CH2 – OH CH – OH R R’ 2o alcohol O K2Cr2O7 / H2SO4 (conc.) C = O R R’ Ketone
  • 11. Aldehydes are quite susceptible to further oxidation to acids - R – CH2 – OH [O] R – C – H || O [O] R – C – OH || O Thus oxidation of primary alcohols is made at the temperature much above the boiling point of aldehyde and thus aldehydes are vapourised out and prevented from being oxidised. 1° alcohol Aldehydes 2° alcohol ketones PCC (Pyridinium chloro chromate) in CH2Cl2 PDC (Pyridinium di chromate) in CH2Cl2 Jones reagent (CrO3+H2SO4) in acetone IMPORTANT Mild Oxidising Agent: 1o alcohols will get oxidised with CrO3/Pyridine, Collin's reagent Ag/O2 at 250oC Selective oxidising agents
  • 12. When the vapours of a primary or a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration. 2. Dehydrogenation reaction CH3 – CH2 – OH Cu 573K CH3 – CHO CH – OH CH3 CH3 Cu 573K C = O CH3 CH3
  • 13. This reaction is used to determine the position of double bond in alkene. 3. By Ozonolysis of alkenes : R – CH = CH2 O3 R – C CH2 | | O O O Ozonide R – CHO + HCHO CH = CH2 R R’ O3 R – C CH2 | | O O O R’ C = O R R’ + HCHO Branched alkenes Ketones Unbranched alkenes Aldehydes Zn dust H2O Zn dust H2O
  • 14. (a) Hydration : With dil H2SO4 & 1% HgSO4 at 60 – 80oC. 4. From Alkyne: CH ≡ CH + H2O CH2 = C – H | O – H H2SO4 & 1% HgSO4 Enol form CH3 – C – H || O Keto form Keto – enol tautomerism CH3 – C ≡ CH + H2O H2SO4 & 1% HgSO4 CH2 = C – CH3 | O – H CH3 – C – CH3 || O Acetylene Aldehydes Other alkynes Ketones
  • 15. Preparation of Aldehydes (specifically) Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction. Cl O C || H2 Pd – BaSO4 O C – H || Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde. This reaction is called Stephen reaction. R – C ≡ N + SnCl2 + HCl Cyanide stannous chloride R – CH = NH H3O + R – CHO Immine 1. From acyl chloride (acid chloride) 2. From nitriles and esters HCHO cannot be prepared by this reaction
  • 16. Alternatively, nitriles are selectively reduced by Di-isoButylaluminium hydride, (DIBAL – H) to imines followed by hydrolysis to aldehydes: R – CN 1. DIBAL – H 2. H2O R – CHO If double bond is present then that double bond is not reduced by DIBAL – H CH3 – CH2 – CH = CH – CN 1. DIBAL – H 2. H2O CH3 – CH2 – CH = CH – CHO Similarly, esters are also reduced to aldehydes with DIBAL-H. CH3– C – O – C2H5 || O 1. DIBAL – H 2. H2O CH3 – CHO + C2H5OH
  • 17. Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons 3. From hydrocarbons Strong oxidising agents oxidise toluene and its derivatives to benzoic acids. As aldehyde group can undergo oxidation easily, methyl group attached to benzene ring first get converted to intermediate that is difficult to oxidise and then finally it is converted to aldehydic group. (i) By oxidation of methylbenzene (toulene) CS2 H3O + CH3 + CrO2Cl2 Toulene CH(OCrOHCl2)2 Chromium complex H O C || Benzaldehyde (a) Use of chromyl chloride (CrO2Cl2): Chromyl chloride oxidises methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde. This is known as Etard reaction.
  • 18. (b) Use of chromic oxide (CrO3): Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be hydrolysed to corresponding benzaldehyde Toulene CH3 + CrO3 + CH3 – C – O O CH3 – C – O H3O + D CHO CH Benzylidene diacetate O – C – CH3 || O O – C – CH3 || O CH Benzylidene diacetate O – C – CH3 || O O – C – CH3 || O
  • 19. Side chain chlorination of toluene gives Benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method of manufacture of benzaldehyde. (ii) By side chain chlorination followed by hydrolysis CH3 Toulene Cl2 / hn CHCl2 Benzal chloride H2O 373 K CHO
  • 20. When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde. (iii) By Gatterman – Koch reaction CO / HCl Anhyd. AlCl3 / CuCl2 CHO Preparation of ketones 1. From acyl chlorides Treatment of acyl chlorides with dialkylcadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives ketones. + CdCl2 R2Cd + 2 Mg Cl X + R2Cd + CdCl2 2 R’ – C – Cl || O Acyl chloride R – Mg – X Grignard’s reagent 2 R’ – C – R || O Ketone
  • 21. Treating a nitrile (cyanide) with Grignard reagent followed by hydrolysis yields a ketone. 2. From nitriles CH3 – CH2 – C ≡ N + C6H5MgBr Anhyd. AlCl3 CS2 CH3 – CH2 – C N – Mg – Br C6H5 H3O+ CH3 – CH2 – C O C6H5 When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminium chloride, it gives the corresponding ketone. This reaction is known as Friedel-Crafts acylation reaction. 3. From benzene or substituted benzenes + R – C – Cl || O C || – R O Dry ether 4. From dry distillation of acids Ca(OH)2 Dry distillationR – C – OH || O R – C – R || O
  • 22. DO IT YOURSELF….. + C2H5 – C – Cl || O1. Anhyd. AlCl3 CS2 ? 2. (C6H5CH2)2Cd + 2CH3COCl ? 3. CH3 – C ≡ C – H Hg+, H2SO4 ? 4. CH3 NO2 1. CrO2Cl 2. H3O+ ?
  • 23. Physical Properties 1. Physical states Methanal is a gas at room temperature. Ethanal is a volatile liquid. Other aldehydes and ketones are liquid or solid at room temperature. 2. Boiling points The boiling points of aldehydes and ketones are higher than hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding. d+ d- C = O d+ d- C = O Dipole – dipole interaction
  • 24. 3. Solubility The lower members of aldehydes and ketones such as methanal, ethanal and propanone are miscible with water in all proportions, because they form hydrogen bond with water. C = O d+ d- H – O H d+ d- d+ d- d+ However, the solubility of aldehydes and ketones decreases rapidly on increasing the length of alkyl chain. All aldehydes and ketones are fairly soluble in organic solvents like benzene, ether, methanol, chloroform, etc. The lower aldehydes have sharp pungent odours. As the size of the molecule increases, the odour becomes less pungent and more fragrant. In fact, many naturally occurring aldehydes and ketones are used in the blending of perfumes and flavouring agents. 4. Odour
  • 25. Chemical Reactions the aldehydes and ketones undergo nucleophilic addition reactions. (i) Mechanism of nucleophilic addition reactions C O d+ d- sp2 Planar C O _ Nusp3 Tetrahedral Nu _ C O _ Nu Slow step H+ Fast step C OH Nu
  • 26. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions (ii) Reactivity Because ketones have two alkyl groups That’s why more stearic hindrance is present In ketone. Ketones show lesser reactivity because +I effect increases electron density on carbonyl carbon. So partial positive charge on carbon decreases R C R O Due to this partial positive charge on this ‘C’ decreases + I + I | C OH | C OH || C OH + – || C OH + – || C OH + – || C OH – + Aromatic aldehydes Positive charge get developed on ortho and para position due to decrease in electron density on these positions. Because of – M or – R effect of carbonyl group as it is EWG. But lesser reactivity towards nucleophilic reactions than aliphatic aldehydes
  • 27. In general, Aliphatic Aldehydes > Aromatic aldehydes > Aliphatic Ketone > Aromatic ketone Reactivity toward nucleophilic reactions decreases
  • 28. Some important examples of nucleophilic addition and nucleophilic addition-elimination reactions (a) Addition of hydrogen cyanide (HCN): Aldehydes and ketones react with hydrogen cyanide (HCN) to yield cyanohydrins. Cyanide and hydroxyl both groups This reaction occurs very slowly with pure HCN. Therefore, it is catalysed by a base and the generated cyanide ion (CN-) Mechanism HCN Base + OH – CN – + H3O + C = O CN – + C O CN – C O CN – H + + C OH CN Tetrahedral complex Cyanohydrin
  • 29. C = O NaHSO3+ C O Na SO3H – + (b) Addition of sodiumhydrogensulphite: Proton transfer C OH SO3Na The hydrogensulphite addition compound is water soluble and can be converted back to the original carbonyl compound by treating it with dilute mineral acid or alkali. Therefore, these are useful for separation and purification of aldehydes. Hydrogensulphite addition compound (Crystalline) Aldehydes react with one molecule of monohydric alcohol in the presence of dry hydrogen chloride to yield alkoxyalcohol intermediate, known as hemiacetals, which further react with one more molecule of alcohol to give a gem – dialkoxy compound known as acetal (c) Addition of alcohols: C = O R H R’OH HCl gas C R H OH O R’ Hemiacetal C R H O R’ O R’ Hemiacetal
  • 30. Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals. C = O R R CH2 – OH + | CH2 – OH HCl gas R R C O O – CH2 – CH2 + H2O ethylene glycol ketal (d) Addition of ammonia and its derivatives: C = O C = NH H2O+C OH N – H H | N – H+ | H | H
  • 31. C = O H2 N – R+ C = N – R Substituted imine (Schiff’s base) C = O H2 N – H+ C = N – H Imine 1o amine C = O H2 N – OH+ Hydroxyl amine C = N – OH Oxime C = O H2 N – NH2+ Hydrazine C = N – NH2 Hydrazone H2 N –+C = O – H2O – H2O – H2O – H2O – H2O C = N– Phenyl hydrazone Phenyl hydrazine
  • 32. C = O H2 N – NH –+ – NO2 O2N – H2O C = N – NH – – NO2 O2N C = O H2 N – NH – C – NH2+ || O – H2O C = N – NH – C – NH2 || O 2,4-DNP-derivatives are yellow, orange or red solids, useful for characterisation of aldehydes and ketones.
  • 33. Aldehydes and ketones are reduced to primary and secondary alcohols respectively by sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4) as well as by catalytic hydrogenation 2. Reduction LiAlH4 / THF or Ether R – CH2 – OH Primary alcohols C = O H Aldehydes R C = O R’ Ketones R NaBH4 / THF or Ether CH – OH R’ Secondary alcohols R H2 / Pt H2 / Pd H2 / Ni (i) Reduction to alcohols: LiAlH4 NaBH4 Strong reducing agent Weak reducing agent THF or ether used as solvent Aldehydes Ketones Carboxylic acids Acid chlorides Nitriles Esters Nitro compounds THF or ether used as solvent Aldehydes Ketones Acid chlorides Conjugate double bond gets reduced Conjugate double bond does not get reduced Isolated double bond does not get reduced Isolated double bond does not get reduced
  • 34. The carbonyl group of aldehydes and ketones is reduced to CH2 group in these reactions. (ii) Reduction to hydrocarbons: Reduction to hydrocarbons Clemmensen reduction Carbonyl group is reduced to CH2 group on treatment with zinc amalgam and concentrated hydrochloric acid C = O HCl Zn – Hg CH2 Wolff – Kishner reduction C = O – H2O NH2 NH2 C = N – NH2 Heat KOH / Ethylene glycol CH2 C = O 420 K Red P CH2
  • 35. 3. Oxidation Aldehydes differ from ketones in their oxidation reactions. Aldehydes Ketones Easily oxidised to carboxylic acids on treatment with common oxidising agents (strong or mild) Cannot be oxidise easily and vigorous oxidation is required Oxidation occurs at room temperature Oxidation occurs at high temperature Cleavage of C – C bond does not take place Cleavage of C – C bond takes place Oxidising agents Strong Mild Nitric acid Tollen’s reagent Potassium permanganate Fehling’s solution Potassium dichromate Only strong oxidising agents are required. Only one carboxylic acid gets formed Mixture of carboxylic acids (having lesser carbon in each than the parent ketone) gets formed
  • 36. Aldehydes Ketones C = O H Aldehydes R [O] R – COOH CH3 – CH2 – CHO [O] CH3 – CH2 – COOH CH3 – CH2 – C – CH2 – CH2 – CH3 || O [O] CH3 – COOH + HOOC – CH2 – CH2 – CH3 CH3 – CH2 – C – CH2 – CH2 – CH3 || O [O] CH3 – CH2 – COOH + CH3 – CH2 – COOH
  • 37. DISTINGUISHING TESTS BETWEEN ALDEHYDES AND KETONES 1. Tollens test (Oxidation by Tollen’s reagent) Bernhard Tollens (1841-1918) was a Professor of Chemistry at the University of Gottingen, Germany. Tollen’s reagent is ammoniacal AgNO3 solution. When aldehydes are heated with Tollens reagent, aldehydes gets oxidised to carboxylate ion and Tollens’ reagent gets reduced into bright silver mirror. 2 AgNO3 + 2NH4OH Ag2O + 2NH4NO3 + H2O Ag2O + 4NH4OH 2 [ Ag (NH3)2] OH + 3H2O –+ RCHO + 2 [ Ag (NH3)2] + 3 OH RCOO + 2Ag ↓ + 2H2O + 4 NH3 + – – silver mirror Only aldehydes show this test positive. Ketones do not show this test positive.
  • 38. 2. Fehling’s test (Oxidation by Fehling’s reagent) Fehling A – Aqueous CuSO4 Fehling B – Alkaline sodium potassium tartarate (Rochelle salt) These two solutions are mixed in equal amounts. On heating aldehyde with this solution a reddish brown precipitate of Cu2O is formed and aldehyde is oxidised to corresponding carboxylate anion. RCHO + 2 Cu + 5 OH RCOO + Cu2O ↓ + 3H2O 2+ – – reddish brown ppt Aromatic aldehydes do not show this test
  • 39. 3. Haloform test Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidised by sodium hypohalite (Cl2, Br2 or I2 in presence of NaOH) to give sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform. (Chloroform, bromoform or iodoform) This oxidation does not affect a carbon-carbon double bond, if present in the molecule. CH3 – C – || O CH3 – CH – | OH Then only this test is positive (Exception – Ethanol) R – C – CH3 || O NaOX R – C – O Na || O – + + CH3 – X Haloform X = Cl, Br, I
  • 40. COMMON EXAMPLES OF HALOFORM TEST Remember only CH3 – C – || O CH3 – CH – | OH and show this test positive. Only exception is ethanol 1. Ethanol and methanol CH3 – CH2 – OH Ethanol CH3 – OH Methanol Positive Negative 2. Acetaldehyde and formaldehyde CH3 – C – H || O H– C – H || O Positive Negative 3. Acetaldehyde and benzaldehyde CHO CH3 – C – H || O Positive Negative 4. Acetophenone and benzaldehyde CHOC – CH3 O Positive Negative 5. Acetone and propanal CH3 – C – CH3 || O CH3 – CH2– C – H || O Positive Negative 6. pentan-2-one and pentan-3-one 7. Isopropyl alcohol and n – propyl alcohol CH3 – CH2– CH2 – C – CH3 || O CH3 – CH2– C – CH2 – CH3 || O Positive Negative CH3 – CH – CH3 | OH CH3 – CH2 – CH2 – OH Positive Negative
  • 41. SOME IMPORTANT PROBLEMS Problem 1 How can you perform following conversions? (a) But-2-ene to ethanal CH3 – CH = CH – CH3 1. O3 2. Zn/H2O 2 CH3 – CHO (b) Cyclohexanol to cyclohexanone | OH K2Cr2O7 / H2SO4 || O Here you can use mild oxidising agents like 1. PCC in CH2Cl2 2. PDC in CH2Cl2 3. Jones reagent (CrO3+H2SO4) in acetone 4. CrO3/Pyridine 5. Collin's reagent Ag/O2 at 250oC (c) Butyne to Butan-2-one CH3 – CH2 – C ≡ CH HgSO4 / H2SO4 CH3– CH2 – C – CH3 || O CHO NO2 (d) p – nitrotoulene to p – nitrobenzaldehyde CH3 NO2 1. CrO2Cl2 / CS2 2. H3O + Here you can also use 1. chromic oxide (CrO3) with acetic anhydride followed by hydrolysis 2. Side chain chlorination followed by hydrolysis at 373 K (Commercial method) (Benzal chloride formed as intermediate) Etard reaction – Chromium complex is formed as intermediate
  • 42. Problem 2 How can you perform following conversions? (a) Propanone to propene (b) Propanal to butanone (c) Benzaldehyde to benzophenone CH3 – C – CH3 || O LiAlH4 CH3 – CH – CH3 | OH H2SO4 CH3 – CH = CH2 CH3 – CH2– C – H || O + CH3 MgBr Dry ether CH3 – CH2– C – H | O Mg Br | CH3 CH3 – CH2– CH | OH | CH3 Mg Br OH + CH3 – CH2– CH – CH3 | OH K2Cr2O7 / H2SO4 CH3 – CH2 – C – CH3 || O CHO KMnO4 / OH - COOH Ca(OH)2 Dry distillation C || O H3O +
  • 43. Problem 3 Complete the following reactions (d) Benzaldehyde to a hydroxyphenylacetic acid HCN / OH - C – CN OH H – C O H – H3O + C – COOH OH H – Alc. KOH D A 1. O3 2. Zn / H2O B + C Alc. KOH D O3 +CH3 – C– CH2 – CH3 | CH3 | Cl CH3 – C CH – CH3 | | O O O CH3 Zn / H2O CH3 – C – CH3 || O B CH3 – C – H || O C CH3 – C = CH – CH3 | CH3 A CH3 – C– CH2 – CH3 | CH3 | Cl (a)
  • 44. Alc. KCN A 1. SnCl2 / HCl 2. H3O+ B CH3 – CH – CH3 | I Alc. KCN 1. SnCl2 / HCl 2. H3O+ CH3 – CH – CH3 | CN A CH3 – CH – CH3 | CHO B 1. CrO2Cl2 / CS2 2. H3O + CH3 CH3 1. CrO2Cl2 / CS2 2. H3O + A CHO CHO A CH3 – CH – CH3 | I (b) CH3 CH3 (c)
  • 45. + H2 Pd / BaSO4 (CH3)2CH – CHO (CH3)2CH – CHOCH3 – CH – C – Cl || O | CH3 (d) A + H2 Pd / BaSO4 + NaOI A + BCH3 – C – C – CH3 || O | CH3 | CH3 (e) CH3 – C – C – CH3 || O | CH3 | CH3 + NaOI CH3 – C – C – O Na || O | CH3 | CH3 – + A + CHI3 B
  • 46. NH2NHCONH2 A CHO NH2NHCONH2 CH = N – NHCONH2 A CHO (f) || O | CHO || O | COO – A || O | CHO (g) [ Ag (NH3)2] OH –+ [ Ag (NH3)2] OH –+
  • 47. REACTIONS DUE TO a HYDROGEN Aldehydes or ketones having at least one a hydrogen show aldol condensation reaction in presence of dilute alkali [e.g. NaOH, Na2CO3 or Ba(OH)2]. Aldol condensation – C– C– C – C – C – C – || O | | H H | | H H H – C – H || O a a'a CHO – C– C– C – C – H || O | | H H Two molecules of same aldehydes or ketones with a hydrogen condense together (combine together) to form b – hydroxy aldehyde or b – hydroxy ketone which undergo dehydration to form a , b unsaturated aldehydes or ketones. –– C –– C –– || O | H This a hydrogen becomes acidic because electron density around this hydrogen decrease due to – I effect of carbonyl carbon. So it can be easily given out as H + in solution if we use base which can extract this proton carbonyl group is EWG and shows – I effect. (a) Simple aldol or self aldol condensation
  • 48. After the removal of H+ the carbanion formed is stable due to resonance. –– C –– C –– || O | H B –– C –– C –– || O – carbanion + BH –– C –– C –– || O – –– C = C –– | O – CH3 – C || O | H H – CH2 – C – H || O CH2 – C – CH2 – C – H | OH O || | H ab b – hydroxy aldehyde (aldol) ab ab a , b – unsaturated aldehyde –H2O D OH – CH2 – CH – CH – C – H | OH O ||| H CH2 – CH = CH – C – H O || Mechanism
  • 49. CH3 – C || O | CH3 H – CH2 – C – CH3 || O OH – CH3 – C – CH2 – C – CH3 | OH O || | CH3 CH3 – C – CH – C – CH3 | OH O || | CH3 | H –H2O D CH3 – C = CH – C – CH3 O || | CH3 b – hydroxy ketone (ketol) ab ab a , b – unsaturated ketone
  • 50. CH3 – C – CH3 || O CH3 – CH2– C – H || O + (b) Crossed aldol condensation Simple aldol or self aldol products CH3 – C – CH3 || O CH3 – C – CH3 || O + OH – CH3 – C – CH2 – C – CH3 | OH O || | CH3 –H2O D CH3 – C = CH – C – CH3 O || | CH3 Four products are possible CH3 – CH2– C – H || O CH3 – CH2– C – H || O + CH3 – CH2– C – CH – C – H | OH | H || CH3 | O OH – –H2O D CH3 – CH2– C = C – C – H | H || CH3 | O
  • 51. CH3 – CH2– C – H || O OH – CH3 – CH2– C – CH2 – C – CH3 | OH | H || O CH3 – C – CH3 || O + –H2O D CH3 – CH2– C = CH – C – CH3 | H || O Crossed aldol products CH3 – C – CH3 || O CH3 – CH2– C – H || O + CH3 – C – CH – C – H | OH O || | H3C | CH3 OH – –H2O D CH3 – C = C – C – H O || | H3C | CH3 In case of crossed aldol condensation, any one aldehyde or ketone has a hydrogen and other does not have a carbon then also reaction is possible as given below. CHO CH3 – C – CH3 || O + OH – CH – CH2 – C – CH3 ||| OH O –H2O D CH = CH – C – CH3 || O
  • 52. Cannizzaro reaction Aldehydes which do not have any a H atom such as HCHO, C6H5CHO undergo self oxidation and self reduction on treatment with conc. Alkali. In this, one molecule is reduced to alcohol and another molecule gets oxidised into salt of carboxylic acid. HCHO + HCHO Conc. KOH CH3OH + HCOOK CHO CHO + Conc. NaOH CH2OH COONa + Self Cannizzaro reaction Crossed Cannizzaro reaction + HCHO CHO Conc. NaOH CH2OH + HCOONa In case of crossed Cannizzaro of any aldehyde and formaldehyde always oxidation of formaldehyde takes place i.e. always salt of formic acid gets formed
  • 53. Electrophilic substitution reactions (aromatic aldehydes and ketones) In case of aromatic aldehydes and ketones, they undergo electrophilic substitution reaction at meta position because – CHO is EWG and shows – R effect. As all EWG are meta directing, so substitution occurs at meta position. (Electron density decreases on ortho and para position so, positive charge gets developed.) | C OH | C OH || C OH + – || C OH + – || C OH + – || C OH – + (a) Halogenation CHO + Cl2 FeCl3 CHO Cl + HCl COCH3 + Cl2 FeCl3 COCH3 Cl + HCl
  • 54. (b) Nitration CHO Conc. HNO3 + Conc.H2SO4 Nitrating mixture CHO NO2 (c) Sulphonation CHO Fuming H2SO4 CHO SO3H COCH3 Fuming H2SO4 COCH3 SO3H
  • 55. USES OF ALDEHYDES AND KETONES 1. 40% HCHO is known as formalin used in preservation of biological specimens 2. Formaldehyde is also used as disinfectant 3. Acetaldehyde is sued for silvering mirrors 4. Benzaldehyde is used in perfume industry 6. Many aldehydes and ketones like vaniline (used as vanilla flavour), cinnamaldehyde (used as cinnamon flavour) used for flavour 5. Acetone is used as solvent in industries as well as paints
  • 56. CARBOXYLIC ACIDS Large number of carboxylic acids are found in nature. Some higher members of aliphatic carboxylic acids (C12 – C18) known as fatty acids. Carbon compounds containing a carboxyl functional group, –COOH are called as carboxylic acids. The carboxyl group, consists of a carbonyl group attached to a hydroxyl group, hence its name carboxyl. Carboxylic acids Aliphatic (RCOOH) Aromatic (ArCOOH) Alkyl group attached to – COOH group Aromatic ring attached to – COOH group
  • 57. NOMENCLATURE AND STRUCTURE OF CARBOXYL GROUP Common system Large number of carboxylic acids are known by their common names because many of the are naturally occurring. The common names end with the suffix –ic acid and have been derived from Latin or Greek names of their natural sources. For example Formic acid HCOOH First obtained from red ants (Latin: formica means ant) Acetic acid CH3COOH First obtained from vinegar (Latin: acetum, means vinegar) Butyric acid CH3CH2CH2COOH First obtained from rancid butter (Latin: butyrum, means butter)
  • 58. IUPAC system Aliphatic carboxylic acids are named by replacing the ending –e in the name of the corresponding alkane with – oic acid. Presence of one –COOH group – oic acid Presence of two –COOH group dicarboxylic acid Presence of three –COOH group tricarboxylic acid Remember priority series 1. f any other functional group present along with – COOH group then that group gets lesser priority and can be used as prefix of that group. 2. Only sulphonic acid has higher priority than that of – COOH group and can be used as suffix.
  • 59. Common nameCompound IUPAC name CH3COOH CH3CH2COOH CH3 – CH – CH – CH2 – COOH | OH 12345 Acetic acid Ethanoic acid Propionic acid Propanoic acid Isobutyric acid 2 – methyl propanoic acidCH3 – CH – COOH | CH3 23 1 CH3 – CH – CH2 – CH2 – CH2 – COOH | Cl 23456 1 5 – chloro hexanoic acid______ 5 – chloro hexanoic acidCH3 – CH = CH – CH2 – CH2 – COOH 23456 1 ______ ______ 3 – hydroxy pentanoic acid
  • 60. Common nameCompound IUPAC name COOH | CH3 COOH 2 1 COOH COOH 1 2 2 – methyl cyclopentane carboxylic acid CH2 – CH2 – COOH 23 1 ______ 3 – phenyl propanoic acid______ ______ Benzoic acid Phthalic acid Benzene –1–2–dicarboxylic acid
  • 61. Common nameCompound IUPAC name Salicylic acid Anisic acid COOH OH 1 2 COOH OCH3 1 2 3 4 Dibasic acids COOH COOH | COOH COOH | CH2 | 2 – hydroxy benzoic acid 4 – methoxy benzoic acid Oxalic acid Malonic acid Ethanedioic acid Propanedioic acid
  • 62. COOH CH2 | CH2 | CH2 | COOH | COOH CH2 | CH2 | COOH | Succinic acid Common nameCompound IUPAC name Butanedioic acid Glutaric acid Hexanedioic acid
  • 63. STRUCTURE OF CARBOXYL GROUP C O H O sp2 hybridisation sp3 hybridisation sp2 hybridisation 120o C O H O Resonance structures: C O H O - + C O H O - +
  • 64. METHODS OF PREPARATION OF CARBOXYLIC ACIDS 1. From primary alcohols and aldehydes (by oxidation) Primary alcohols Oxidising agents Aldehydes 1. KMnO4 in alkaline medium [KMnO4 / OH -] Followed by hydrolysis 2. KMnO4 in acidic medium [KMnO4 / H+] 3. K2Cr2O7 in acidic medium [K2Cr2O7 / H+] 1. CrO3 2. Pyridinium chloro chromate (PCC) 3. Pyridinium dichromate (PDC) 4. Jones reagent (CrO3+H2SO4) in acetone CH3 – CH2 – CH2 – OH 1. KMnO4 / OH - 2. H3O+ CH3 – CH2 – COOH CH3 – CH – CH2 – CHO CH3 | PCC CH3 – CH – CH2 – COOH CH3 |
  • 65. Primary and secondary alkyl groups are oxidised in this manner while tertiary group is not affected. 2. From alkylbenzenes Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate. The entire side chain is oxidised to the carboxyl group irrespective of length of the side chain. CH3 KMnO4 – KOH Heat COO K – + H3O+ COOH CH2 – CH2 – CH3 KMnO4 – KOH Heat COO K – + H3O+ COOH
  • 66. Nitriles are hydrolysed to amides and then to acids in the presence of H+ or OH– as catalyst. 3. From nitriles and amides R – CN H + or OH– H2O R – C – NH2 || O H + or OH– D R – C – OH || O CONH2 H + or OH– D COOH Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which in turn give corresponding carboxylic acids after acidification with mineral acid. 4. From Grignard reagents R Mg X + O = C = O Dry ether R– C O O Mg _ + H3O+ R – C – OH || O Mg X OH +
  • 67. Anhydrides are hydrolysed to corresponding acid(s) with water. 5. From acyl halides and anhydrides Acid chlorides when hydrolysed with water give carboxylic acids or more readily hydrolysed with aqueous base to give carboxylate ions which on acidification provide corresponding carboxylic acids. C6H5 – C O C6H5 – C O O || || R – C – Cl || O H2O OH / H2O _ R – C – O || O _ + Cl _ H3O+ R – C – OH || O + HCl R – C – OH || O H2O 2 C6H5– C – OH || O C6H5 – C O C2H5 – C O O || || H2O C6H5– C – OH || O C2H5– C – OH || O +
  • 68. 6. From esters COOC2H5 COOH + C2H5OH H3O+
  • 69. PHYSICAL PROPERTIES Aliphatic carboxylic acids up to nine carbon atoms are colourless liquids at room temperature with unpleasant odours. The higher acids are wax like solids and are practically odourless due to their low volatility. 1. Physical states 2. Boiling point R C O OH d – d+ C R O OHd+ d – Intermolecular H – bonding Carboxylic acids have highest boiling point among all functional groups in organic compounds.
  • 70. 3. Solubility R C O OH d – d+ H – O H d+ d- d+ H – O H d+ d- d+ Benzoic acid, the simplest aromatic carboxylic acid is nearly insoluble in cold water. Simple aliphatic carboxylic acids having upto four carbon atoms are miscible in water due to the formation of hydrogen bonds with water. The solubility decreases with increasing number of carbon atoms. Higher carboxylic acids are practically insoluble in water due to the increased hydrophobic interaction of hydrocarbon part. Carboxylic acids are also soluble in less polar organic solvents like benzene, ether, alcohol, chloroform, etc.
  • 71. CHEMICAL REACTIONS OF CARBOXYLIC ACIDS Acidity of carboxylic acids Carboxylic acids react with active metals like sodium, potassium etc. to give hydrogen gas 2 R – C – OH + 2 Na || O R – C – O Na || O _ + + H22 Carboxylic acids react with alkalis to form salt and water (neutralisation reaction) R – C – OH + NaOH || O R – C – O Na || O _ + + H2O Carboxylic acids react with weaker bases like sodium carbonate, sodium bicarbonate etc. to form salt and carbon dioxide is evolved R – C – OH + NaHCO3 || O R – C – O Na || O _ + + H2O + CO2
  • 72. Carboxylic acids dissociate in water to give resonance stabilised carboxylate anions and hydronium ion. R – C – OH + H2O || O R – C – O || O _ + H3O + R C O O _ R C O O _ R C O O - Carboxylate ion Resonance structures of carboxylate ion Resonance hybrid
  • 73. Now, consider the same reaction, R – C – OH + H2O || O R – C – O || O _ + H3O + Equilibrium constant for this reaction can be given as, K = [RCOO ] . [H3O+] _ [RCOOH] . [H2O] ∴ K [H2O] = [RCOO ] . [H3O+] _ [RCOOH] ∴ Ka= [RCOO ] . [H3O+] _ [RCOOH] pKa = – log10 Ka Remember Higher Ka Value stronger is the acid Higher pKa value weaker is the acid For strong acid pKa < 1 For moderately strong acid 5 > pKa > 1 For weak acid 15 > pKa > 5 For extremely weak acids pKa > 15
  • 74. EFFECT OF SUBSTITUENTS ON THE ACIDITY OF CARBOXYLIC ACIDS If EWG group is attached to R chain in – COOH group then acidity of carboxylic acid increases EWG C O O - – I Case 1:Acidity of carboxylic acid depends upon which EWG group is attached to – COOH Increase in acidity of acid is in order. Ph < I < Br < Cl < F < CN < NO2 < CF3 e.g. Arrange the following acids in increasing order of acidic strength CH3 – CH2 – CH – CH2 – COOH | NO2 (I) CH3 – CH2 – CH – CH2 – COOH | I (II) CH3 – CH2 – CH – CH2 – COOH | F (III) CH3 – CH2 – CH – CH2 – COOH | (IV)
  • 75. Case 2: Acidity of carboxylic acid depends upon no. of EWG attached to carbon chain No. of EWG increases acidity of acid also increases e.g. Arrange the following acids into their increasing order of acidic strength F – C – CH2 – COOH F | F | (I) CH2 – CH2 – COOH | F (II) CH – CH2 – COOH | F | F (III) CH3 – CH2 – COOH (IV) Case 3: Acidity of carboxylic acid depends upon position of EWG in carbon chain. CH3 – CH2 – CH2 – CH – COOH | CN (I) CH3 – CH – CH2 – CH2 – COOH CN | (II) CH2 – CH2 – CH2 – CH2 – COOH CN | (III) CH3 – CH2 – CH – CH2 – COOH CN | (IV) e.g. Arrange the following acids into their increasing order of acidic strength
  • 76. If EDG group is attached to R chain in – COOH group then acidity of carboxylic acid decreases EDG C O O - + I e.g. groups like – R, – OR etc. CH3 – C – CH2 – COOH CH3 | CH3 | (I) CH2 – CH2 – COOH | CH3 (II) CH – CH2 – COOH | CH3 | CH3 (III) CH3 – CH2 – COOH (IV) e.g. Arrange the following acids into their increasing order of acidic strength Same can be applied for aromatic acids as well.
  • 77. 1. Formation of anhydride Carboxylic acids on heating with mineral acids such as H2SO4 or with P2O5 give corresponding anhydride CH3 C O OH + C CH3 OH O H+ , D Or P2O5 , D CH3 C O C CH3 O O 2. Esterification R – OH + R’ COOH H+ R COOR’ + H2O
  • 78. 3. Reactions with PCl5, PCl3 and SOCl2 R – C – OH + PCl5 || O R – C – Cl + POCl3 + HCl || O 3 R – C – OH + PCl3 || O 3 R – C – Cl + H3PO3 || O The hydroxyl group of carboxylic acids, behaves like that of alcohols and is easily replaced by chlorine atom on treating with PCl5, PCl3 or SOCl2. R – C – OH + SOCl2 || O R – C – Cl + SO2 + HCl || O
  • 79. Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature give amides. 4. Reaction with ammonia CH3– C – OH + NH3 || O D – H2O COOH COOH + NH3 D – 2H2O CH3 – C – O NH4 || O – + Ammonium acetate CH3– C – NH2 || O Acetamide COO NH4 COO NH4 – + – + Ammonium phthalate Strong heating – NH3 Phthalamide C – NH2 C – NH2 || O || O C C || O || O NH Phthalimide
  • 80. Carboxylic acids are reduced to primary alcohols by lithium aluminium hydride or better with diborane. 5. Reduction Diborane reduces carboxylic acid and unsaturation selectively. Diborane does not reduce functional groups such as ester, nitro, halo, etc. RCOOH RCH2OH 1. LiAlH4 2. H3O+ RCOOH RCH2OH B2H6 Carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with sodalime (NaOH and CaO in the ratio of 3 : 1). The reaction is known as decarboxylation. 6. Decarboxylation RCOONa NaOH & CaO Heat RH + Na2CO3 Alkali metal salts of carboxylic acids also undergo decarboxylation on electrolysis of their aqueous solutions and form hydrocarbons having twice the number of carbon atoms present in the alkyl group of the acid. The reaction is known as Kolbe electrolysis
  • 81. Carboxylic acids having an α-hydrogen are halogenated at the a-position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give a-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction. 7. Halogenation R – CH2 – COOH 1. X2 / Red phosphorus 2. H3O+ R – CH – COOH | X (X = Cl, Br) Aromatic carboxylic acids undergo electrophilic substitution reactions in which the carboxyl group acts as a deactivating and meta-directing group. They however, do not undergo Friedel-Crafts reaction because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group. 8. Electrophilic substitution of aromatic acids COOH NO2 COOH HNO3 + H2SO4 COOH Br COOH Br2 / FeBr3
  • 82. 1. Hexanedioic acid is used in the manufacture of nylon-6, 6. 2. Esters of benzoic acid are used in perfumery. 3. Sodium benzoate is used as a food preservative. 4. Higher fatty acids are used for the manufacture of soaps and detergents. USES OF CARBOXYLIC ACIDS
  • 84. Q.1 Write the structures of products of the following reactions O + HO – NH2 H+ O H2 N – NH –+ – NO2 O2N H2N – NH – C – NH2 || O R – CH = CH – CHO +
  • 85. Q. 2. Write chemical reactions to affect the following transformations: (i) Butan-1-ol to butanoic acid (ii) Benzyl alcohol to phenylethanoic acid (iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid CH3 – CH2 – CH2 – CH2 – OH [O] CH3 – CH2 – CH2 – COOH CH2 – OH Mg Ether CH2 – Br CH2 – CN KCN CH2 – COOH 1. Reduction 2. H3O+ D Br NO2 Mg Br NO2 Dry ice (CO2) Dry Ether C NO2 O Mg BrO C NO2 OHO HBr H3O+ Mg Br OH +
  • 86. (vi) Butanal to butanoic acid. (iv) 4-Methylacetophenone to benzene-1,4-dicarboxylic acid (v) Cyclohexene to hexane-1,6-dioic acid COCH3 CH3 KMnO4 / KOH COOK COOK H3O+ COOH COOH benzene-1,4-dicarboxylic acid Terephthalic acid KMnO4 / H2SO4 Heat COOH COOH CH3 – CH2 – CH2 – CHO [O] CH3 – CH2 – CH2 – COOH
  • 87. Q. 3 Show how each of the following compounds can be converted to benzoic acid. (i) Ethylbenzene (ii) Acetophenone (iii) Bromobenzene C2H5 KMnO4 / KOH COOK H3O+ COOH COCH3 1. KMnO4 / OH _ 2. Hydrolysis COOH + CH3COOH Br Mg Ether Mg Br Dry ice (CO2) Dry Ether C O Mg BrO C OHO H3O+ Mg Br OH +
  • 88. (iv) Phenylethene (Styrene) CH = CH2 KMnO4 / KOH COOK H3O+ COOH
  • 89. Q. 4 Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents. (i) PhMgBr and then H3O+ (ii) Tollens’ reagent C O H + PhMgBr Dry Ether CBr Mg O H Ph H3O+ CHO H Ph Mg Br OH + C O H Tollen’s reagent Ammoniacal solution of AgNO3 C O O _ + 2 Ag ↓ + 4NH3 + 2H2O
  • 90. (iii) Semicarbazide and weak acid C O H (iv) Excess ethanol and acid H2N – NH – C – NH2 || O + H+ C O H C2H5 – OH C2H5 – OH H+ C H OC2H5 C2H5 O + H2O (v) Zinc amalgam and dilute hydrochloric acid C O H Zn – Hg / HCl CH3
  • 91. Q. 5. Which of the following compounds would undergo aldol condensation, which the Cannizzaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction. (i) Methanal (ii) 2-Methylpentanal (iii) Benzaldehyde (iv) Benzophenone (viii) Butan-1-ol (ix) 2,2-Dimethylbutanal (v) Cyclohexanone (vi) 1-Phenylpropanone (vii) Phenylacetaldehyde HOME WORK
  • 92. Q. 6 How will you convert ethanal into the following compounds? (ii) But-2-enal (iii) But-2-enoic acid (i) Butane-1,3-diol CH3 – CHO Dil. NaOH Self aldol CH3 – CH – CH2 – CHO | OH CH3 – CH – CH2 – CH | OH | OH D – H2O CH3 – CHO Dil. NaOH Self aldol CH3 – CH – CH2 – CHO | OH NaBH4 CH3 – CH = CH – CHO D – H2O CH3 – CHO Dil. NaOH Self aldol CH3 – CH – CH2 – CHO | OH CH3 – CH = CH – CHO Mild oxidising agent CH3 – CH = CH – COOH
  • 93. Q. 7. How will you bring about the following conversions in not more than two steps? (i) Propanone to Propene (ii) Benzoic acid to Benzaldehyde (iii) Ethanol to 3-Hydroxybutanal CH3 – C – CH3 || O CH3 – CH – CH3 | OH CH3 – CH = CH2 COOH NaBH4 H2SO4 D SOCl2 COCl CHO Pd / BaSO4 H2 CH3 – CH2 – OH [O] CH3 – CHO CH2 – C – CH2 – C – H | OH O || | H Dil. NaOH Self aldol
  • 94. (iv) Benzene to m-Nitroacetophenone (v) Benzaldehyde to Benzophenone CH3COCl / Anhyd. AlCl3 Friedel – Craft acylation C – CH3 || O HNO3 + H2SO4 C – CH3 || O NO2 (vi) Bromobenzene to 1-Phenylethanol COOHCHO [O] SOCl2 COCl Anhyd. AlCl3 C || O Br Mg Ether Mg Br 1. CH3CHO 2. H2O H3C – C – H | OH Mg Br OH +
  • 95. (viii) Benzoic acid to m- Nitrobenzyl alcohol (vii) Benazaldehyde to α-Hydroxyphenylacetic acid CHO CH – CN | OH CH – COOH | OH NaCN / HCl H+ / HCl COOH HNO3 + H2SO4 COOH NO2 B2H6 CH2OH NO2