Reactions which Yield Carboxylic Acids
Oxidation of Aromatic Side-Chains with Neutral Permaganate
Warm, neutral permaganate anion will oxidize aromatic side-chains which contain at least one benzylic hydrogen to the corresponding carboxylic acid.
Primary alcohols can be oxidized smoothly to the corresponding carboxylic acid with either CrO3/H2SO4 or sodium dichromate.
Acidic MnO4- will oxidize an alkene bearing at least one alkyl or aryl substituent to the corresponding carboxylic acid. Terminal alkenes are converted to CO2 under these conditions.
Aldehydes are smoothly oxidized to the corresponding carboxylic acid with either CrO3/H2SO4 or sodium dichromate.
Aldehydes (but not ketones) are oxidized by Ag2O in aqueous ammonia to give the carboxylic acid and metallic silver. This is used as a qualitative test for aldehydes since the silver metal is deposited in a thin film, forming a "silver mirror" (the Tollens test).
Acidic MnO4- will oxidize a ketone to the corresponding carboxylic acid, in this case, splitting the ring. The reaction is slower than the oxidation of alkenes, allowing disubstituted alkene carbons to be oxidized to the ketone, without significant over-oxidation.
Nitriles can be hydrolyzed to the corresponding carboxylic acids. Typically, vigorous conditions are required (heat and concentrated acid).
Grignard reagents react with CO2 to yield carboxylic acids. This is an important method for the preparation of carboxylic acids and yields are generally good.