A kinetic study of the reaction of sulphuryl chloride with some phenols

Abstract

The kinetic studies of some substituted phenols in their reactions with sulphuryl chloride in chlorobenzene and at 25°C showed that the clectrophile involved is molecular sulphuryl chloride (Cl+-SO- ₂-Cl). In the poly methyl phenol studied, the magnitude of the effect of -CH₃ groups on the reactivity of the phenol molecule in this reaction suggested that the mechanism involves heterolytic attack of molecular sulphuryl chloride on the benzenoid nucleus. The kinetic study of 3,5-dimethyl anisole was done in benzene and showed similar effects. The reaction in all the phenols and anisole was found to be bimolecular and of second order.

The ether and the phenols were activated towards electrophilic attack particularly in the para position. This was supported by the analysis of the products formed in the reaction which also helped to trace the mechanism via which the electrophile substitutes a hydrogen of the benzenoid nucleus.

The compounds studied were: 2.4-xylenol. 2,6-xylenol. 3.5-xylenol. 2,3,5-trimethyl phenol. 2,3,6-trimethyl phenol. 3.5-ditertiary butyl phenol. 3.5-dimethyl anisole.

The kinetic study of 3,5-xylenol was studied in great detail and was extended to three solvents: benzene, chloro-benzene and o-dichlorobenzene. In all the three cases a considerable change in second order rate constant was observed and indicated that the reaction was heterolytic in nature. The increase in the rate constant was also observed with the increase in the concentration of 3,5-xylenol in the reaction mixture and was explained due to the formation of a pi-complex between xylenol or its chlorinated products (4-chloro, 3,5-xylenol and 2,4-dichloro, 3,3-xylenol) and sulphuryl chloride and its high reactivity. With the increase in xylenol concentration more pi-complex was suggested to be formed thereby affecting the rate of reaction. Kinetics of 3,5-xylenol was also compared with 2,4,6-D ₃-3s5-xylenol and O-deutero-3,5-xylenol to understand the other factors affecting the mechanism and to establish the rate determining step. Different quantities of 3,5-xylenol was also reacted with sulphuryl chloride in different mixture of solvents (benzene and chlorobenzene) to illustrate the effect of polarity of the solvent and the concentration of xylenol content on the rate of reaction.

The explained behaviour of the pi-complex formed between 4-chloro, 3,5-xylenol and sulphuryl chloride was justified by the increase in second order rate constant of 3,5-dimethyl anisole, when reacted in presence of 4-chloro xylenol, with sulphuryl chloride. This study was extended to pi-complexes of 2,4-dichloro, 3,5-xyleno1,4-chloro,3,5-dimethyl anisole and 3,5-ditertiary butyl phenol formed with sulphuryl chloride. The nature and structure of T -complexes was also studied by u.v. and n.m.r. spectroscopy.

The reactivity of the phenols can be described in the order: 2,3,5-Me ₃-phenol > 3,5-xylenol > 2,3,6-Me₃-phenol and 3,5-dimethyl anisole > 2,4-xylenol > 2,6-xylenol > 3,5-ditertiary butyl phenol.