Studies on the Autoxidation of Phenylacetylene

Abstract Phenylacetylene is oxidized slowly by molecular oxygen at 110°C. The main oxidation products are benzoic acid, benzoic anhydride, and benzaldehyde. Besides the oxidation, thermal dimerization, oligomerization, and polymerization processes also take place. As individual products 1,4‐diphenylbut‐1‐yn‐3‐ene and 1,3,5‐triphenylbenzene were identified. About 80% of the phenylacetylene consumed are converted into products of low volatility which could not be detected by gas chromatography. The autoxidation of acetylenic hydrocarbones [1] preferably yields products of the attack at CH bonds in α‐position to the CC triple bond. An attack at the CC riple bond was a first proved in the case of phenylacetylene, which besides polymeric products yielded benzaldehyde, acetophenone, and organic acids [2]. Later, in the causes of the isomeric octynes [3] and of various 1‐Phenylalk‐1‐ynes [4] an attack at the CC triple bond was also proved. As the primary products of the oxidative attack at the CC triple bond short‐lived oxirenes or their valence isomers, the corresponding ketocarbenes are to be expected. Indeed, their rearrangement products were found in the oxidation mixtures of both the isomeric ocytnes [3] and the 1‐phenylalk‐1‐ynes [4]. Other products of the oxidative attack at the CC triple bond are lower carboxylic acids, formally produced by oxidative cleavage of the CC triple bond [3, 4].