Monocarboxylic acids of the benzene series

This chapter focuses on the monocarboxylic acids of the benzene series. The preparation of Benzoic acids from arenes, toluenes, aryl halides, and arynes is discussed. Optimum conditions for the oxidation of alkylarenes to benzoic acids, avoiding decarboxylation, have been determined. Monoalkylbenzenes are oxidized to benzoic acids by oxygen in the presence of a cobalt/manganese catalyst. The oxidation of toluenes (especially nitrotoluenes) with potassium permanganate at 95 ºC in nitrobenzene/water under phase-transfer conditions gives good yields of benzoic acids. Another well established approach involves the photochlorination of toluenes, to give benzotrichlorides, followed by hydrolysis. Benzyne can be generated from either bromobenzene, or chlorobenzene, by treatment with sodamide. The aryne is then reacted in situ with O-silyl enolates of carboxylic esters to form bicyclic adducts. These adducts, after hydrolysis, yield 2-alkylbenzoic acids. An improved methodology for the oxidative decarboxylation of toluic acids to cresols using copper salts and cupric oxide has been discussed.