Autoxidation of cyclohexanecarboxylic Acid‐l‐¹⁴C

Abstract

Oxidation of cyclohexanecarboxylic acid-lJ4C by molecular oxygen at 205'C in the presence of cupric salt of cyclohexanecarboxylic acid and magnesium oxide yielded nearly equal amounts of cyclohexanone and cyclohexene. When cupric salt and magnesium oxide were omitted, only cyclohexanone was obtained. In both cases the label distribution in the cyclohexanone was determined. This showed that in the presence of cupric salt and magnesium oxide and at a temperature of about 20S°C, cyclohexanone forniation comes about by attachment of oxygen to either the tertiary carbon atom (54%) o r to one of the neighbouring secondary carbon atoms (447:) of the cyclohexanecarboxylic acid molecule. In the absence of cupric salt and magnesium oxide over 90% of the cyclohexanone is formed by attachment of oxygen to the tertiary carbon atom of the cyclohexanecarboxylic acid.When the oxidation is carried out in the presence of cupric salt and magnesium oxide. but at a lower temperature ( I 65°C). cyclohexanone formation is very slow; the label distribution indicated formation through oxidative attack at the tertiary carbon atom only. The fact that at 205°C and in the presence of cupric salt and magnesium oxide, oxidJtive attack at the @carbon atoms of cyclohexanecarboxylic acid takes place, is tentatively explained by assuming the formation of the 2-carboxycyclohexyl radical (11) from the cupric salt of cyclohexanecarboxylic acid.When a mixture of oxygen, nitrogen and steam is passed, at 205"C, through cyclohexanecarboxylic acid containing small amounts of cupric salt of this acid and magnesium oxide, cyclohexanone and cyclohexene are formed in nearly equal amounts 1. In order to obtain some information about the mechanism of this reaction, we have repeated the reaction using cyclohexanecarboxylic acid-1 -14C.