An electron spin resonance study of reactions of aromatic hydrocarbons with sulphuric acid

Abstract

The object of this research was to investigate the utility of the e.p.r. technique itself, and where necessary, in conjunction with other spectroscopic techniques, in studying the complex reactions of polyalkylated aromatic hydrocarbons which have low first ionisation potentials, with sulphuric acid. The formation of immediate electron paramagnetic resonance (e.p.r.) signals from hexamethylbenzene (H.M.B.), pentamethylbenzene (P.M.B.) and durene on admixture with sulphuric acid has been investigated in the presence and absence of ultra-violet light. The kinetics of the H.M.B. system have been studied, and the activation energy measured. The prolonged reaction of hexamethylbenzene with 98% sulphuric acid has been investigated and leads to the formation of the 4-methylene-1,1,2,3,5,6-hexamethyl-cyclohexa-2,3-diene radical cation, as a result of Jacobsen rearrangement of hexamethylbenzene. This radical cation is also formed rapidly by exposure of a solution of 4-methylene-1,1,2,3,5,6-hexamethyl-cyclohexa-2,3-diene in 98% sulphuric acid to ultra-violet light. Finally, a mechanism is postulated for the reactions of hexamethylbenzene with 98% sulphuric acid.