Radiochlorine exchange reactions with sulfuryl chloride

Graduation date: 1964As part of a continuing study of sulfur containing non-aqueous\ud solvents, the present investigation was undertaken in an effort to obtain\ud a better understanding of the solvent sulfuryl chloride. The\ud primary object of the investigation involved a study of the rate of\ud radiochlorine exchange between sulfuryl and thionyl chloride in mixtures\ud of the two, the radioisotopic tracer chlorine-36 being used.\ud The principal motivation for such experiments rested in the hope of\ud being able to find some evidence relative to the possible significance\ud of an ionic dissociation process for sulfuryl chloride. The system\ud was of particular interest in presenting analogies to at least two\ud related types of systems previously studied, namely the thionyl\ud chloride-thionyl bromide system (where rapid radiosulfur exchange\ud was observed) and the thionyl chloride-sulfur monochloride system\ud (where negligible radiochlorine exchange occurred). The system\ud was further of interest in the light of the previous observation of a\ud rapid chlorine exchange between sulfuryl chloride and the solute\ud pyridinium chloride (in chloroform solution). Another point of\ud some pertinence related to the fact that earlier research had shown\ud that, between these two substances, little if any radiosulfur exchange\ud occurred, and the suggestion had been made that a rapid radiochlorine\ud exchange might result if the two substances interacted in an acid-base\ud type of ionization equilibrium, thionyl chloride acting as a basic,\ud chloride ion donor.\ud It was found in this work that radiochlorine exchange between\ud thionyl chloride and sulfuryl chloride was, at best, very slow, with\ud an exchange half time, t1/2, of at least 35 days or more. The rate of\ud the exchange did not appear to vary greatly, at least in apparent order\ud of magnitude, over the concentration range from a five fold excess of\ud sulfuryl chloride to a two fold excess of thionyl chloride, the value\ud of the order of magnitude at 25°C being 10⁻¹ g-atoms 1⁻¹day⁻¹. The\ud obtaining of precise rate data was, however, hampered both by the\ud extreme slowness of the reaction and by the considerable difficulty in\ud a clean cut reactant separation at the end of each experiment, a\ud factor which resulted in a large and rather irreproducible apparent\ud zero time exchange.\ud A single experiment was done investigating the radiochloride\ud exchange between sulfuryl chloride and the initially labeled solute tetramethylammonium chloride. Despite incomplete solution of the\ud salt in the solvent, 84% exchange occurred in the time of the experiment\ud (14.75 hours). It appears most likely that, if solution had been\ud complete, exchange would also have been complete within the period\ud of the experiment, and in all probability in a far shorter time, probably\ud less than an hour.\ud The results are taken to imply that sulfuryl chloride neither\ud undergoes any significant chloride ion dissociation, nor any acid-base ionic interaction with thionyl chloride. They further suggest\ud that exchange of the solvent with ionic chloride solutes probably\ud occurs via either a rapid association equilibrium or a bimolecular\ud equilibrium. The results demonstrate the hazard of a too indiscriminate\ud application of the solvent systems interpretation of chemical\ud phenomena in non-aqueous systems. Many processes can be better\ud understood in less restricted terms, Lewis acid-base concepts, for\ud example, being particularly useful. Further investigations of sulfuryl\ud chloride exchange reactions, particularly with other basic and\ud some acidic solutes appear most inviting