of alkyl benzene with chromic acid or acidic or alkaline potassium permanganate. The entire side chain is oxidised to –COOH group irrespective of the length of the side chain. Example OH - /KMnO COOH Toluene Benzoic acid (O) Evaluate yourself ) What happens when n-propyl benzene is oxidised using H + / KMnO ? ) How will you prepare benzoic acid using Grignard reagent.
. Physical Properties of carboxylic acids. i) Aliphatic carboxylic acid upto nine carbon atoms are colour less liquids with pungent odour. The higher members are odourless wax like solids.
ii) Carboxylic acids have higher boiling point than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more association of carboxylic acid molecules through intermolecular hydrogen bonding. XII U12-Carbonyl XII U12-Carbonyl - - - - R R Inter molecular hydrogen bonding In fact, most of the carboxylic acids exist as dimer in its vapour phase. iii) Lower aliphatic carboxylic acids (up to four carbon) are miscible with water due to the formation of hydrogen bonds with water.
Higher carboxylic acid are insoluble in water due to increased hydrophobic interaction of hydrocarbon part. The simplest aromatic carboxylic acid, benzoic acid is insoluble in water. iv) Vinegar is to % solution of acetic acid in water. Pure acetic acid is called glacial acetic acid.
Because it forms ice like crystal when cooled. When aqueous acetic acid is cooled at . K, acetic acid solidifies and forms ice like crystals, where as water remains in liquid state and removed by filtration. This process is repeated to obtain glacial acetic acid.
. Chemical properties of carboxylic acids. Carboxylic acid do not give the characteristic reaction of carbonyl group C = O as given by the aldehydes and ketones. as the carbonyl group of carboxylic acid is involved in resonance: The reactions of carboxylic acids can be classified as follows: A) Reactions involving cleavage of O – H bond.
B) Reactions involving cleavage of C – OH bond. C) Reactions involving – COOH group. D) Substitution reactions involving hydrocarbon part.