imporatance of diazonium salts

1. Organic Chemistry
Group 1
Topic Importance of diazonium salts
Roll no. 09,21,29,37,51,109
Section A
Semester 6th
Department Chemistry
Instructor Ma’am Ruqayya

2. Importance of diazonium salts

3. What are diazonium compounds
• Diazonium compounds or diazonium salts are a group
of organic compounds sharing a common functional
group R−N+2X−
• Where R can be any organic group, such as an alkyl or
an aryl, and X is an inorganic or organic anion, such as
a halogen.
• Diazonium salts, especially those where R is an aryl
group, are important intermediates in the organic
synthesis of azo dyes.
• Diazonium salts, especially those where R is an aryl group, are
important intermediates and have found wide applications in
organic synthesis.
• Since their first discovery in 1858, several prominent named
reactions associated with arene diazonium salts have evolved
throughout the development of more than one century.
• X=Cl–, Br–, BF4
–
• R=an alkyl or aryl
group.
• They have two
nitrogen atoms with
one being charged.
• Examples:
Benzenediazonium
chloride (C6H5N2
+Cl–),
benzenediazonium
hydrogensulphate
(C6H5N2
+HSO4
–).

4. Diazonium compounds
• By varying the chemical structures of the amines that are
diazotized (the diazo components) and of the compounds with
which they react (the coupling components), colours throughout
the visible spectrum are imparted to dyes applicable to many
types of fibers by several techniques.
• The diazonium group can be replaced by numerous atoms or
groups of atoms, often with the aid of copper or a copper salt;
these reactions make possible the preparation of a wide variety of
aromatic derivatives.
• Chemical reduction of aromatic diazonium salts leads to
formation of hydrazine derivatives.

5. Nomenclature
Arenediazonium salts are
named by adding the suffix
diazonium to the name of
parent aromatic
hydrocarbon
Examples:

6. Stability
Aryldiazonium salts are
stable because of
dispersal of positive
charge over benzene ring
due to resonating
structures.

7. Preparation of arenediazonium salts
• This process of converting an aromatic primary amine into diazonium salt is called
diazotization.
• Diazotization should be carried out at low temperature since at higher
temperature benzene diazonium salt reacts with water to form phenol.
• Aromatic amines substituted with electron withdrawing groups require more
concentrated acids than unsubstituted amines because of their weak basic
character

8. Diazotization
Diazonium ions are prepared by diazotization
• A procedure in which a primary aromatic amine (ArNH2) is treated
with a source of nitrous acid (HNO2). Typically this involves adding
sodium nitrite (NaNO2) to an aqueous acidic solution containing the
amine.
• This leads to diazonium salts, which can be isolated if the counter
ion is non-nucleophilic.
• Aqueous solutions of diazonium salts are unstable above 5 °C. One
can isolate diazonium compounds as tetrafluoroborate salts, which
are stable at room temperature.
• It is often preferred that the diazonium salt remain in solutions, but
they do tend to supersaturate.

9. Diazotization
1.Attack of
aniline
1.Formation
of
nitrosamine
1.Attack of
water
Mechanism

10. Other methods
• Phenol reacts with diazonium
salt.
• Gives orange-red precipitates.
With
phenol
• Aniline reacts with diazonium
salt.
• Gives aniline yellow
precipitates.
With
aniline

11. Properties of Diazonium Salts:
• They are ionic in nature.
• Aryl diazonium salts are colorless crystalline
solids.
• Benzene diazonium chloride is soluble in water
but reacts with it only when warmed.
• They are water soluble.
• Benzene diazonium fluoroborate is not soluble
in water. It is pretty stable at room temperature.
• Diazonium salts are formed by coupling
reactions.
• Coupling reactions: In these reactions diazonium
salt acts as electrophile and brings about
substitution in some other electron rich
aromatic ring such as phenols or aryl amines.

12. Applications of diazonium salts
• Diazonium salts was firstly use to produce
water-fast dyed fabrics by immersing the
fabric in an aqueous solution containing
the diazonium compound, and the fabrics
are immersed with the help of a solution of
the coupler (the electron-rich ring that
undergoes electrophilic substitution).
• In nanotechnology diazonium salts like 4-
chlorobenzenediazonium tetrafluoroborate
is commonly use in single wall nanotubes.

13. Applications of diazonium salts
• Diazonium salts are light sensitive and break down under near UV or violet
light. This property has led to their use in document reproduction.
• In this process, paper or film is coated with a diazonium salt. After contact
exposure under light, the residual diazo is converted to a stable azo dye with
an aqueous solution of coupler.
• A more common process uses a paper coated with diazo, coupler and an acid
to inhibit coupling after exposure the image is developed by a vapor mixture
of ammonia and water which forces coupling.
• The nature of the anions affects stability of the salt. Aryl diazonium
perchlorates, such as nitrobenzene diazonium perchlorate, have been used to
initiate explosives.
• Diazonium compounds are standard reagents used in synthesis of organic
compounds, especially aryl derivatives.

14. Nanotechnology
• In a nanotechnology application of diazonium
salts, 4-chlorobenzenediazonium
tetrafluoroborate is very efficient in
functionalizing single wall nanotubes.
• In order to exfoliate the nanotubes, they are
mixed with an ionic liquid in a mortar and pestle.
• The diazonium salt is added together with
potassium carbonate, and after 15 minutes of
grinding at room temperature the surface of the
nanotubes are covered with chlorophenyl groups
with an efficiency of 1 in 44 carbon atoms.
• These added substituents prevent the tubes from
forming intimate bundles due to large cohesive
forces between them which is a recurring
problem in nanotube technology.

15. Preparation of phenol from diazonium salt
• When an aromatic primary amine is treated with nitrous (NaNO2 + HCl)
acid at 273 – 278 K, diazonium salts are obtained.
• These diazonium salts are highly reactive in nature.
• Upon warming with water, these diazonium salts finally hydrolyses to
phenols.
• Phenols can also be obtained from diazonium salts by treating it with
dilute acids.

16. Azotization of phenol
• Phenol is dissolved in sodium hydroxide
solution to give a solution of sodium
phenoxide.
• The solution is cooled in ice, and cold
benzenediazonium chloride solution is
added.
• There is a reaction between the
diazonium ion and the phenoxide ion
and a yellow-orange solution or
precipitate is formed.
• The product is one of the simplest of
what are known as azo compounds, in
which two benzene rings are linked by a
nitrogen bridge.

17. Preparation of other organic compounds
Sandmeyer Reaction
• Aromatic diazonium salts can be taken and reacted with copper (I) chloride
to form an aryl chloride in a transformation called the Sandmeyer reaction,
named after its discoverer Traugott Sandmeyer in the late 1800’s.
• The diazonium salt undergoes the loss of a molecule of nitrogen and
ultimately the diazo group on the aromatic ring is replaced by a chlorine
atom, supplied by our copper (I) chloride reagent.

18. Diazonium salts in Iodobenzene synthesis
• Diazonium salts can be reacted with KI to produce
aryl iodides.
• Iodobenzene is commercially available, but it can be
prepared in the laboratory from aniline via the
Sandmeyer reaction.
• In the first step, the amine functional group is
diazotized with hydrochloric acid and sodium nitrite.
• Potassium iodide is added to the resultant
phenyldiazonium chloride, causing nitrogen gas to
evolve.
• The product is separated by steam distillation

19. Formation of dyes
•Red dye
•First group of azo-compounds are neutral which are
used as azoic combination (or ingrain) dyes.
•An example is para red which is prepared by coupling
of 2-napthol with p-nitrobenzenediazonium salt.
•Orange dye
• The second group of azo-compounds posses either a
sulfonic acid group or an amino group which are
generally adsorbed directly on the fiber from
aqueous solution.
• Examples are orange II (an acidic dye) and Bismarck
brown R (a basic dye)

20. Formation of indicators
• Azo-compounds that contain both
an acidic and a basic group can be
utilized as indicators.
• since the colors of the conjugate
acid and the conjugate base are
different.
• Examples are methyl orange and
methyl red which are prepared
by coupling of dimethylaniline
with diazotized sulfanilic acid and
diazotized anthranilic acid,
respectively.

21. As indicators
• Azo compounds contain a highly delocalised
system of electrons which takes in both
benzene rings and the two nitrogen atoms
bridging the rings.
• The delocalization can also extend to things
attached to the benzene rings as well.
• If white light falls on one of these molecules,
some wavelengths are absorbed by these
delocalized electrons.
• The color you see is the result of the non-
absorbed wavelengths.
• The groups which contribute to the
delocalization (and so to the absorption of
light) are known as a chromophore.

22. As indicators
• Modifying the groups present in the molecule can have an
effect on the light absorbed, and so on the colour you see.
You can take advantage of this in indicators.
• Methyl orange is an azo dye which exists in two forms
depending on the pH.
• As the hydrogen ion is lost or gained there is a shift in the
exact nature of the delocalisation in the molecule, and that
causes a shift in the wavelength of light absorbed. Obviously
that means that you see a different color.
• When you add acid to methyl orange, a hydrogen ion
attaches to give the red form. Methyl orange is red in acidic
solutions (in fact solutions of pH less than 3.1).
• If you add an alkali, hydrogen ions are removed and you get
the yellow form. Methyl orange is yellow at pH's greater than
4.4.
• In between, at some point there will be equal amounts of the
red and yellow forms and so methyl orange looks orange.

23. Formation of quinone
• Many natural and artificial coloring substances (dyes and pigments) are quinone
derivatives. They are second only to azo dyes in importance as dyestuffs, with
particular emphasis on blue colors. Alizarin (1,2-dihydroxy-9,10-anthraquinone),
extracted from the madder plant, was the first natural dye to be synthesized from
coal tar.
• The ortho and para diamines and aminophenol readily oxidize to give quinones.
• Both classes of compounds can be readily prepared by diazo-coupling followed by
reduction.

24. References
• Principles of Organic Synthesis
R. O. C. NORMAN F.R.S.
• Professor ofChemistry, University of York
• Mo, Fanyang, et al. "Recent applications of arene diazonium
salts in organic synthesis." Organic & biomolecular
chemistry11.10 (2013): 1582-1593.
• Roglans, Anna, Anna Pla-Quintana, and Marcial Moreno-Manas.
"Diazonium salts as substrates in palladium-catalyzed cross-
coupling reactions." Chemical reviews 106.11 (2006): 4622-4643.
• www.chemguide.co.u
• www.theglobaltutors.com
• www.simplylearnt.com

25. Any question

26. Thank
you