B. Pharm. (Honours) Part-IV Practical, Medicinal Chemistry-II, MANIK

Laboratory Manual
Course: 410
Subject: Practical - Medicinal Chemistry-II
Prepared By
Md. Imran Nur Manik
M.Pharm
Department of Pharmacy
University of Rajshahi
Rajshahi-6205, Bangladesh
Available at
Essential Pharma documents
www.pharmacydocs.blogspot.com

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Serial No. Date Name of the experiment Page No.
01 10.10.11 Synthesis of Paracetamol. 2 – 5
02 12.10.11 Synthesis of acetanilide. 6 – 7
03 15.10.11 Synthesis of Esters. 8 – 10

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Experiment No. 01 Date: 10.10.11
Name of the experiment: Synthesis of Paracetamol.
Principle:
Paracetamol is an analgesic and antipyretic that may be conveniently prepared in the
laboratory from para-aminophenol. Para-aminophenol is readily acylated with acetic
anhydride to give paracetamol.
Reaction:
Mechanism of action:
The amino group is more readily acetylated than the phenolic hydroxyl group.
The following steps are involved in the formation of paracetamol:
Step-1: First step involve the formation of acetylium ion. The reaction enhanced by
proton donation by concentrated acid.
Step-2: Amino group of para-aminophenol dissociates as follows:
Step-3: Acetylium ion attacks the anion at nitrogen atom to form para-acetyl
aminophenol or paracetamol.
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Reagents:
1. Para-aminophenol 4. Concentrated H2SO4
2. Acetic anhydride 5. Distilled water
3. Alcohol
Apparatus:
1. Beaker 5. Funnel
2. Filter paper 6. Stirrer
3. Water bath 7. Glass tube
4. Measuring cylinder 8. Vacuum pump
Procedure:
1. 5.5 gm of para-aminophenol and 15 ml of distilled water were taken in a 250 ml
conical flask.
2. 8 ml of acetic anhydride was added to it and was stirred. The reaction was stirred
vigorously and then it was warmed on a water bath at 40-50C for 5 minutes. The volume of
reaction mixture was decreased by heating on water bath. After that, 1-2 drops of conc.
H2SO4 was added in the solution.
3. After 10 minutes when solid was dissolved, it was then cooled in refrigerator until the
crystals were appeared and was filtered by a vacuum pump. The solid portion was acetyl
derivative which was washed with little cold water.
4. It was then recrystallized from 75 ml hot water and 15 ml alcohol. The final yield was
then filtered by vacuum pump and was dried upon filter paper in the hot air oven. The dried
solid crystals were taken and weighed.
Calculation:
Molecular weight of para-aminophenol = 109
Molecular weight of paracetamol = 151
109 gm of para-aminophenol yields 151 gm paracetamol
1 gm of para-aminophenol yields =
109
151
gm paracetamol
Thus, gm of para-aminophenol yields =  gm paracetamol
= gm paracetamol
Now, upon drying the weight of paracetamol crystal was = gm
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Practical yield weight of aspirin
 of paracetamol yields =
yieldlTheoretica
yieldObtained
 100
=   100
=
Result:
The percentage yield of paracetamol from the experiment was =
Determination of melting point: The synthesized paracetamol showed the melting point
at 169C.
Comment:
The percent yield of paracetamol was the normal.
It may be due to the following reasons:
i. A portion of the supplied sample may remain during unreacted or byproduct may
be formed by various side reactions.
ii. A portion of the product may be lost during washing and drying.
iii. Weight variation may be occurred due to instrumental defect.
iv. Amount of reagent and starting materials taken may not be exact.
v. Supplied reagent and starting material may not be pure.
vi. Cooling or heating may not be done properly.
vii. Filter paper may absorb a portion of crystal.
Properties of paracetamol:
1. Crystaline powder and after purification it was white color.
2. Slightly bitter taste and odorless.
3. Melting point range is 169-170C.
4. It is soluble in 7 parts of ethanol and 70 parts of water.
Indication: Paracetamol has both analgesic and antipyretic actions.
1. As analgesic, paracetamol is used for the treatment of:
i. Headache
ii. Toothache
iii. Dysmenorrhoea
iv. Neuralgia
v. Rheumatic pain
vi. Arthralgia
.
2. As antipyretic, paracetamol is used for the treatment of influenza. It is often used in
place of aspirin in order to avoid possibility of Roy’s syndrome.
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Side effects:
1. Early:
i. Nausea iii. Anorexia
ii. Vomiting iv. Abdominal pain
2. Delayed:
i. Hepatic necrosis v. Skin rash
ii. Renal tubular necrosis vi. Pancytopenia
iii. Hypoglycemic coma vii. Urticaria
iv. Leucopenia
Dose:
Single dose: 500 mg or 1 gm dauily. Dose should not be exceeding 4 gm per day.
Dose for children is about 30 mg/kg body weight.
Precaution:
A doctor should consult before administration of paracetamol to a child age less than 3
years. In children under 12 years, dose should not exceed 1-2 gm. Single dose should not be
given at an interval of less than 4 hours.
Dosage form:
 Tablet  Elixir
 Solution  Suspension
 Syrup  Capsule
Contraindication:
 Hypersensitivity to paracetamol  Liver disease
 Glucose-6-phosphate dehydrogeneous deficiency  Kidney disease
Market preparation:
Trade name Manufacturer name
Napa Beximco
Apa Opsonin
Ace Square
Fast Acme
Reset Incepta
Aceta Biopharma
Zerin Jayson
Parapyrol GSK
ATP General
Remalgin Reman drug
Xpa Aristopharma
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Name of the experiment: Synthesis of acetanilide.
Principle:
Acetanilide can be synthesized from aniline by acetylation in presence of acetic
anhydride. Acetic acid and zinc is used as catalyst as reducing agent.
Reaction:
Apparatus:
i. Round bottom flask vi. Pipette
ii. Reflux condenser vii. Suction pump
iii. Conical flask viii. Glass rod
iv. Water bath ix. Hot air oven
v. Beaker x. Filter paper
Reagents:
i. Aniline
ii. Acetic anhydride
iii. Distilled water
iv. Glacial acetic acid
v. Zinc dust
vi. Ethanol
vii. Conc. H2SO4
Purposes:
1. To synthesize an acetanilide by reaction of aniline and acetic anhydride.
2. To purify acetanilide by crystallization method from water.
Procedures:
1. 2.33 gm 2.5 ml of aniline was placed to a 150–250 ml round bottom flask.
2. 3.06 gm acetic anhydride 2.5 ml was gradually added to a reaction mixture followed
by glacial acetic acid 1.44 gm or 1.5 ml and zinc dust 0.025 mol = 1.65 gm or sodium
metabisulfite.
3. The reaction mixture was heated at 50–60 C until the mixture was dried.
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4. The reaction mixture was cooled at room temperature and there was added 75 ml ice
water in it.
5. The precipitation of crude acetanilide was collected by suction pump and dried in hot
air oven.
6. Recrystallization: The crude acetanilide was dissolved in 5 ml of ethanol. Then 100
ml boiled water was added in the mixture gradually. The volume of solvent must be added till
to turbidity and further heated to clear off the solution.
7. The solution was cooled at room temperature or in an ice water bath, the crystal was
filtered at pump and dried in the hot air oven.
Calculation:
Molecular weight of aniline M1 = 93
Molecular weight of acetanilide M2 = 135
Taken amount of aniline W1 = 2.33 gm
Found amount of acetanilide W2 = gm
% yield of acetanilide =
11
22
/
/
MW
MW
× 100
=  × 100
= %
Result:
The yield of acetanilide was % having the melting point 114 C.
Precaution:
Aniline and acetanilide are toxic chemicals. So care should be taken to avoid contact
with them.
Mode of action:
Since acetanilide is in the same class of drugs of acetaminophen or paracetamol, it shows
analgesic and antipyretic activity. It produces analgesic action by elevation of the pain
threshold and antipyresis through the action on the hypothalamic heat regulating centre.
Pharmaceutical uses:
1. Acetanilide has analgesic and antipyretic properties. It is in the same class of drug as
paracetamol.
2. It is used as an inhibitor in hydrogen peroxide and use to stabilize cellulose ester.
3. It is used as a precursor in penicillin synthesis and other pharmaceuticals and its
intermediates.
Md.
Imran
Nur
Manik

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Name of the experiment: Synthesis of Esters.
Introduction:
The esters are a group of organic compounds best known for their interesting odours.
Many perfumes and artificial flavorings are esters. Esters are formed when a carboxylic acid
reacts with an alcohol in the presence of a strong acid. A general equation for the formation
of esters is:
The R and R' represents alkyl groups such as methyl, ethyl, or propyl. The esters are
named after the compounds from which they are formed. The first part of the name comes
from the alcohol and the second part of the name comes from the carboxylic acid. Thus
when ethyl alcohol (ethanol) combines with acetic acid, the resulting ester is named ethyl
acetate.
The synthesis of an ester must be done in the presence of an acid in order to push the
reaction closer to completion. The reaction can be reversed by adding a strong base, such as
NaOH. The acid that you will be using as a catalyst in this experiment is sulfuric acid.
Many of the aromas of natural fruits and flowers are due to simple esters. Octyl ethanoate
has the odor of oranges, while apricots owe their characteristic aroma to pentyl butanoate.
Mechanism for reaction for acid catalyzed esterification:
Step 1: An acid/base reaction. Protonation of the carbonyl makes it more electrophilic.
Step 2: The alcohol O functions as the nucleophile attacking the electrophilic C in the
C=O, with the electrons moving towards the oxonium ion.
Step 3: Deprotonation of the alcoholic oxygen.
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Step 4: Protonation of –OH group of compound makes it good leaving group.
Step 5: The electrons of adjacent oxygen helps to leaving the group as a water molecule.
Step 6: Deprotonation of the oxonium ion reveals the carbonyl in the ester product.
Apparatus:
i. Beaker (250 ml) vii. Full face shield
ii. 2 test tubes viii. Centigram balance
iii. Thermometer ix. Glazed paper
iv. Test tube rack x. Plastic gloves
v. Safety goggles xi. Graduated cylinder (10ml)
vi. Dropper pipette xii. Hotplate
Reagents:
i. Methanol iv. Salicylic acid
ii. Ethanol v. Concentrated sulfuric acid
iii. Glacial acetic acid
Procedure:
1. Two test tubes were taken and labeled them as A and B.
2. Following reagent in the following ratio:
A. 1 ml acetic acid 1 ml ethanol
B. 1 g salicylic acid 1 ml methanol
3. 4 drops of conc. sulfuric acid was carefully added to each test tube.
4. About 150 ml of water was putted in a 250 ml beaker. The test tubes were placed into
the water and heated the water on a hot plate to a temperature of 60°C. The test tubes were
heated in the hot water bath for 15 minutes. It was ensured that, the water bath remained at
approximately 60°C for that period of time.
5. The test tubes were cooled for a few minutes and then immersed in an ice bath. This
step was added to prevent any test tubes from cracking.
6. 5 ml of distilled water was added to each of the test tubes. This step was included to
dilute the ester and soften its odour.
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7. The odour of the contents of each of the test tubes was carefully noted. It was done by
wafting the odours of the test tubes toward the nose. The observations were documented in the
table.
Required Combinations:
i. Methyl alcohol + acetic acid, benzole acid, salicylic acid
ii. Ethyl alcohol + acetic acid, benzoic acid, salicylic acid
Result:
Test
tube
Alcohol Carboxylic
acid
Ester
Produced
Odor of Ester
1 Ethyl alcohol Acetic acid Ethylacetate Fingernail Polish Remover
2 Ethyl alcohol Benzoic Acid Ethylbenzoate Fruity
3 Methyl alcohol Salicylic acid Methyl Salicylate Wintergreen
Safety Precautions:
1. Concentrated sulfuric acid is a strong oxidizing agent. It will start a fire if mixed
incorrectly with any of the alcohol or other acids used in this experiment. Use exactly as
directed.
2. All of the liquid acids used in this experiment are corrosive to skin, eyes and clothing.
While working on this experiment, ware safety goggles, full face shield, gloves and lab
apron. Wash spills and splashes off the skin and clothing immediately, using plenty of water.
3. The alcohol and the organic acids used in this experiment are all flammable. Be sure
all burners and other flames in the laboratory are extinguished before starting the experiment.
4. The detection of odours should be done cautiously. Breathing the vapors of some of
these esters can cause sore throat, dizziness, headache and drowsiness. The test tube should
be held about 30 cm away and 15 cm below the nose. Waft the odor toward the nose, sniffing
cautiously, once or twice. Should not breathe deeply while sniffing.
Md.
Imran
Nur
Manik

B. Pharm. (Honours) Part-IV Practical, Medicinal Chemistry-II, MANIK

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B. Pharm. (Honours) Part-IV Practical, Medicinal Chemistry-II, MANIK