Abstract
A method for sulphonating polystyrene by means of sulphur trioxide in sulpholane has been developed. The method has been used to prepare specimens of poly(styrenesulphonic acid) having different degrees of sulphonation. These polyacids have been used to catalyse the benzidine rearrangement of hyarazobenzene. The rate of the benzidine rearrangement when catalysed by poly(styrenesulphonic acid) is very much greater than when it is catalysed by simple monomeric acids. For example, at an acid concentration of 0.0500N the value of the pseudo-first-order rate constant, k', for the rearrangement catalysed by poly(styrene-sulphonic acid) having a molar percentage sulphonation of 35.8 is 290 times the value of k' for the rearrangement catalysed by hydrogen chloride under identical conditions of concentration and temperature. From a study of the variation of k' with polyacid concentration, and comparison of the products of the polyacid catalysed rearrangement with those obtained by other workers for the rearrangement catalysed by simple monomeric acid, it is concluded that the rearrangement follows the same mechanistic scheme whether catalysed by monomeric or polymeric acid. The rate-enhancement brought about by the polyacid was found to increase with increasing degree of sulphonation of the polyacid. The accelerative effect of the polyacid is attributed to the increase in the concentration of both hydrogen ions and the first conjugate acid of hydrazobenzene in the region of the solution close to the polyanion, brought about by the strong electrostatic field created by the polyion. A semi-quantitative treatment of the accelerative effect is given.