Question

The reaction to form 4-nitroacetanilide from the acetanilide by electrophilic aromatic substitution. Nitrating mixture is a mixture of concentrated sulfuric acid and concentrated nitric acid. Glacial acetic acid and acetanilide are used.

i) For this experiment, a low temperature (< 30 °C) was maintained throughout the addition of the nitrating mixture. What was the main purpose for maintaining a low temperature?

ii)How did you (or how could you) confirm that your product was 4-Nitroacetanilide and not some other compound? If the product is not pure,what do you think is the most likely impurity present

Answer 1

i) The reaction to form 4-nitroacetanilide from the acetanilide by electrophilic aromatic substitution, low temperature is maintained throughout the addition of nitrating mixture because its a exothermic reaction, so this is controlled by chilling and slow addition of reagents. Glacial acetic acid being a polar solvent it dissolves acetanilide and while sulphuric acid is added temperature increases beyond 30 degrees. Being exothermic its tendency to form 4-nitroacetanilide decreases so it must be maintained at low temperature.

ii) We observe light yellow colour at the end which confirms the product 4-nitroacetanilide and if the colour is dark yellow the impurity present is 4-nitroaniline and its difficult to remove from 4-nitroacetanilide.