Relative rates of sulfonation of linear and branched long-chain alkylbenzenes

Relative rates of sulfonation of a series of 1-phenylalkanes and isomeric branched-chain alkylbenzenes by gaseous SO3 have been determined. It has been shown that the composition of the mixture undergoing sulfonation has an important bearing on the actual relative rate constant (k(rel)) values obtained. This is taken as evidence for the involvement of pyrosulfonic acids as the actual sulfonating species involved in the sulfonation reaction. Consistent k(rel) values have been obtained by using an "active solvent" in 10-fold excess as the sulfonating medium. Whereas the branched-chain isomers show very little variation in their rates of sulfonation, the rates of sulfonation of the 1-phenylalkanes increase as the length of the alkyl chain decreases.