Question

Describe the three sources of loss in the lab preparation of methyl benzoate from benzoic acid.

One source is mechanical.

Answer 1

Ans:

In the lab preparation of methyl benzoate, other two sources of losses in the final yield of the product, i.e. methyl benzoate could be from the chemical reactions. The esterification reaction is as follows:

C6H5COOH + MeOH ----- > C6H5COOMe + H2O

In this reaction the benzoic acid is refluxed with the methanol in the presence of conc. sulfuric acid. Then later the excess alcohol is distilled off and the product is extracted in ether and washed with bicarbonate and redistilled to get teh desired product. Two sources of error could be as follows:

1. The esterification reaction is stopped before its completion. Generally one hour is required to complete the reaction. This will form the less quantity of the methyl benzoate.

2. The ether layer is washed more than the required time and also if more than 10 % bicarbonate solution is used. This may result in the hydrolysis of the methyl benzoate back to the benzoic acid and thereby will reduce the yield.