PREPARATION OF ACETYL SALICYLIC ACID (ASPIRIN)
REQUIREMENTS:
Apparatus:
Beakers,
Test tubes, Balance, Spatula, Water bath, Stirrer, Filter paper etc
Chemicals:
Salicylic
acid ……………………………………….. 10gm
Acetyl
chloride …………………………………….. 7.5gm
Pyridine
…………………………………………….. 7.0ml
THEORY:
·
White crystals, commonly needle like or
white, crystalline powder; odourless; taste, slightly acid; stable in dry air.
·
Solubility:
It
is soluble in 300 parts of water, in seven parts of alcohol, in 20 parts of
solvent ether, in 17 parts of chloroform and with decomposition in solutions of
alkali hydroxide and of alkali carbonates.
·
Melting
point: It is about 136o. The substance is being placed
in the heating bath at about 130o and the temperature being raised
at the rate of 4o to 6o per minute.
PROCEDURE:
1)
I
took salicylic acid (10gm) in a beaker and then I dissolved in pyridine (07ml),
to get the clear solution.
2)
Then I added acetyl chloride (7.5gm)
portion wise.
3)
I placed the beaker in water bath at 50-60
oC for 30minutes with continuous stirring.
4)
Then the contents were transferred in 300ml cold water.
5)
I filtered it with the help of filter
paper, so that I got clear crystals.
6)
I washed it and dry it by pressing in filter paper
7)
Then I weighed the dried crystals.
PRECAUTIONS:..
1)
Wash the beakers before solution
preparation.
2)
Weigh the ingredient carefully
3)
Prepare clear solution of salicylic acid
4)
Mentain the temperature at 50-60 oC.
5)
Before re-weighing, must dry the crystals.
TO
DETERMINE THE MELTING POINT AND PURIFICATION OF CRUDE ASPIRIN BY CRYSTALIZATION
REQUIREMENTS:
Apparatus:
Melting
pint apparatus (Gallenkemp), Beakers, capillary tubes, Balance, Spatula, Water
bath, Stirrer, Filter paper etc
Chemicals:
Crude aspirin, ethanol
PROCEDURE:
Melting
point determination:
8)
I take crude aspirin and inserted some
quantity in capillary tube.
9)
Then I placed the capillary tube in the
Gallenkemp apparatus.
10) By
this I determined the melting point of crude aspirin.
Crystallization of crude aspirin:
11) I
weighed crude aspirin in a beaker and then added ethanol portion wise so that
clear solution of aspirin prepared.
12) Then
I placed it in a water bath for a few
minutes.
13) When
the supersaturated solution obtained, I taken off the beaker.
14) Then
I filtered the content with the help of filter paper and I placed it at
room temperature for a few minutes.
15) I
kept the crystals until it become fully dried.
16) Then
I weighed the dried crystals and determined the percent (%) yield.
PRECAUTIONS:
6)
Take three reading of crude aspirin on
Gallenkemp apparatus.
7)
Wash the beakers before solution
preparation.
8)
Before re-weighing, must dry the crystals
CALCULATIONS
AND RESULT
Result of crude aspirin
melting point
Average reading of aspirin melting point =
Result of crystallization of
crude aspirin
Weight of the filter paper (A) =
Weight of the filter paper + aspirin crystals (B) =
Weight of
wet aspirin crystals (C) =
=
=
Weight of dry aspirin
crystals (D) =
Weight of crude aspirin (E) =
By the help of this we can find the
%age yield, using the following formula;
=
ASSAY
OF ASPIRIN POWDER
REQUIREMENTS:
Apparatus:
Beakers,
Volumetric flask, Test tubes, Balance, Spatula etc
Chemicals:
Sodium
hydroxide (0.5 M), Hydrochloric acid (0.5 M), Ethanol, Phenolphthalin.
PROCEDURE:
1)
I dissolved 0.5gm of aspirin powder in 10ml of ethanol to form a clear solution.
2)
I added 40ml of 0.5M sodium hydroxide
solution in it and it was boiled for 10minutes.
3)
A blank titration was carried out with
0.5M sodium hydroxide solution and 0.5M HCl solution.
4)
The solution was then titrated against
0.5M HCl solution.
5)
The difference between two readings was
calculated, which would give volume of sodium hydroxide used to neutralize
aspirin.
6)
The difference between the two reading was calculated and the
following factor was then used to calculate the aspirin content.
2ml of 0.5M NaOH = 0.045gm of aspirin
CALCULATIONS Table
Preparation of 0.5M Hydrochloric
Solution
= 4.1 ml per 100ml
Preparation
of 0.5M Sodium Hydroxide Solution
01M Sodium hydroxide solution =
40g/1000ml
0.5M Sodium hydroxide solution = 20g per
1000ml
0.5M Sodium hydroxide solution = 20 mg per ml
Preparation
of 0.5M Aspirin Solution
01M Aspirin solution = 90g/1000ml
0.5M Aspirin solution = 45g per 1000ml
0.5M Aspirin solution = 45 mg per ml
Determination
of Percent Purity
Aspirin + 2NaOH + CH3COONa + H2O
180gm
40gm
Volume of 0.5M HCl solution used to
neutralize blank 0.5M NaOH =
Volume of 0.5M HCl soln used to neutralize
Aspirin solution =
Volume of 0.5M NaOH solution used to
neutralize Aspirin =
=
1ml of 0.5M NaOH solution neutralize = of Aspirin
11ml of 0.5M NaOH solution neutralize =
= of Aspirin
So;
Percent purity = × 100
= purity
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