**These questions are dealing with my formal lab report the synthesis of acetani
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Question
**These questions are dealing with my formal lab report the synthesis of acetanilide**
1. should a small volume of the solvent be used for rinsing the pure crystals?
2. why should the rinsing solvent be cold?
3. A hot solution of a particular compound was allowed to cool to room temperature. After waiting a few minutes, it was noticed that the crystallization had not taken place. Discuss two ways to induce crystallization?
4. What properties are necessary and desirable for a solvent in order that it is well suited for recrystallizing a particular organic compound?
5. The solubility of acetanilide in hot water (5.5 g/100 ml at 100 degrees C), and it's solubility in cold water (0.53 g/100ml at 0 degrees C) is significant. What would be the maximum theoretical percent recovery from the crystallization of 5.0 g of acetanilide from 100 ml water. (assuming the solution is chilled at 0 degrees Celsius
Explanation / Answer
Preparation of acetanilide involves
1. Preparation of acetophenone from benzene
2. Preparation of acetophenone oxime from aceto phenone
3. Preparation of acetanilide from acetophenone oxime.
In the third step it involves Bechmann's rearrangement.
This rearrangement occurs in presence of H+ or PCl5 .
a)So first around 4g. of acetophenone oxime is dissolved in minimum amount of ether and then aroung 6g. of PCl5 is added with stirring.
b)Then it is allowed to stay for 30 min. without disturbing. Then the ether is distilled off on water bath.
c) To the residue around 50ml of water is added. This mixture is boiled and then filtered.
d) The filtrate is allowed to cool then crystals of acetanilide separates out.
e) Then it is filtered using bucknel funnel.
f) Finally the crystals are rinsed with water.
1.The amount of water used for rinsing should be small.
2. Acetanilide dissolves in hot water but not in cold water. So while rinsing water should be cold.
3. Some times crystals the solute won't be obtained from its solution. In that case we can induce crystallisation by
a) Scratching the walls of the glass with pipette or any fine dropper.
b) We must add a pure crystal of the required compound if it is available.
4. a)We must choose the solvent in such a way that it should dissolve the compound when it is cold and impurities when it is hot.
b) At the same time when the solvent is cooled ,the impurities will remain soluble and the compound should precipitate.
5. When heated, all of acetanilide is dissolved in water, this is then filtered and allowed to cool. Then it is kept in an ice bath, thus the temp is 0C and acetanilide is no longer soluble.
So the final max % recovery should be:
(5.0-0.53)/5.5 x 100
= 81.27%
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