Aromatic sulphonation. Part XXXVII. The sulphur trioxide sulphonation of toluene and some o-dialkylbenzenes and benzocycloalkenes

Abstract

Isomer distributions for the sulphonation of toluene, two o-dialkylbenzenes, and three benzocycloalkenes with sulphur trioxide in nitromethane and nitrobenzene as a solvent have been determined. The degree of ortho-substitution with toluene is independent of the substrate conversion. The 3-:4-sulphonic acid ratio decreases in the order indane > tetralin > o-xylene > o-diethylbenzene > 6,7,8,9-tetrahydro-5H-benzocycloheptene. The relatively high value for indane is explained in terms of enhanced hyperconjugative stabilization of the transition state involved in the sulphur trioxide sulphonation of indane at the 3-position.