Question

When toluene is nitrated； the proportions of ortho-, meto- and para-nitrotoluenes that are formed are 59%, 4% and 37% respectively. These three compounds are liquids with boiling points of 221, 232 and 238 °C respectively. A methyl group on a benzene ring can be oxidized to a carboxyl group with KMn04 solution. Nitrobenzoic acids are solids at room temperature. Discuss what purification techniques you would use (and how efficient they are likely to be) in order to isolate pure samples of ortho- and para- nitrobenzoic acids, starting from toluene.

Answer 1

The recrystallization method helps well in purifying the solids. So, in the given case also, recrystallization is the suitable purification technique to isolate pure samples of ortho- and para-nitro benzoic acids.

Explanation: The boiling point of ortho-nitrobenzoic acid (221 ^oC) is more than that of para-nitrobenzoic acid (238 ^oC). Hence, para-nitrobenzoic acid precipitates first in the solution, which can be filtered out. The filtrate contains pure ortho-nitrobenzoic acid, whcih can be precipitated easily from the filtrate.