The main raw material for the synthesis of this substance – toluene (methylbenzol), which has the chemical formula C6H5CH3. In the course of different reactions, its methyl group (CH3) is converted by oxidation to carboxyl (COOH). The General scheme of the reactions is this:
2С6Н5СН3 + 3О2 = 2С6Н5СООН + 2Н2О
In laboratory conditions, the oxidation of toluene to produce either potassium permanganate (KMnO4) or chromium compounds in higher oxidation States (e.g. chromium anhydride CrO3, potassium dichromate K2Cr2O7), that is, substances that easily decompose to form oxygen. In industry, the oxidation is performed with pure oxygen with the participation of manganese or cobalt catalysts.
Benzoic acid in laboratories can be obtain in other ways. For example, from brombenzol (С6Н5Вг), using the "Grignard" - complex compounds consisting of alkyl- (or aryl-) halide ion and magnesium. The final stage of the reaction when adding hydrochloric acid) goes thus:
C6H5CO2MgBr + HCl = C6H5COOH + MgBrCl
Benzoic acid produced by hydroxylation of benzoic alcohol. The reaction takes place by this mechanism (depicted in highly simplified form):
2С6Н5СОН (benzaldehyde) + HE- = С6Н5СОН (benzyl alcohol) + С6Н5СООН (benzoic acid).It bears the name "Cannizzaro Reaction", in honor of the chemist who first described and who spent it. In another way, it is called "disproportionation Reaction of aldehydes".