The thermal reaction of toluene and iodine and some related processes

Abstract

The work reported in this thesis arose from some observations made by R.B. Cundall¹ in the laboratories at St Andrews while he was investigating the pyrolysis of methyl iodide. An attempt to use toluene as a radical acceptor resulted in the production of some hydrogen iodide, and Cundall attempted a brief investigation into its source. The reaction of iodine with toluene was suspected, and in some initial experiments, the reaction was investigated in a flow system.

In these experiments it was shown that stilbene and dibenzyl condensed out at the furnace exit, and that benzyl iodide, hydrogen iodide and unreacted toluene and iodine condensed out in the analysis traps.

The only other reference to this reaction are recorded in Beilstein², where it is noted that the prolonged heating of toluene and iodine vapours together yields hydrogen iodide and other products. Other investigations have shown that the prolonged refluxing of toluene, to which iodine has been added, produced no hydrogen iodide.

The aim of the work described in this thesis was to investigate the products and kinetics of the reaction. It was hoped that additional data on the question of the bond strength of the side chain (C-H) link in toluene might be obtained since a study of the bromination of the latter had recently yielded a new value for this bond dissociation energy. The results quoted in later sections of this thesis on the reaction of toluene with iodine are explained by a primary reaction between the hydrocarbon and an atom of iodine. This step produces a benzyl radical and hydrogen iodid, and appears to be markedly inhibited by the addition of excess hydrogen iodide. The presence of dibenzyl and stilbene in the products rendered it necessary to investigate the reaction of dibenzyl with iodine, and which hydrogen iodide. The results of these investigations are given in later sections.

Before dealing with the experimental work of this thesis, and discussing it, a brief survey is given of some relevant themes and studies reported in the literature, and which form a background against which this present investigation has to be considered.