( ii) From alkyl benzenes Alkyl benzene when treated with strong oxidising agent like H2CrO4( chromic acid), acidic or alkaline KMnO4 gives benzoic acid.
( iii) From acid derivatives All acid derivatives like amides( RCONH2), acid halides( RCOCl), esters( RCOOR ‟), acid anhydrides( RCO-O-COR) on hydrolysis give carboxylic acids. All acid derivatives break from RCO +.
( iv) From nitriles and amides Nitriles are hydrolysed to amides and then to acids in the presence of H + or OH- as catalyst. Mild reaction conditions are used to stop the reaction at the amide stage.
( v) From Grignard reagents Grignard reagents react with carbon dioxide( dry ice) to form salts of carboxylic acids which in turn give corresponding carboxylic acids after acidification with mineral acid.