Modern Views on the Chemistry of Vulcanization Changes. II. Role of Hydrogen Sulfide

Abstract

Abstract 1. The normal addition of hydrogen sulfide to olefins is catalyzed by very small proportions of sulfur, but the rate of addition is too slow to provide a satisfactory basis for the hydrogen sulfide-actuated mechanism of vulcanization. 2. The main products of the sulfur-catalyzed (polar) reaction of hydrogen sulfide with polyisoprenes are substituted pentamethylene sulfides, derived by intramolecular normal addition of the initially formed monothiols. 3. The main products of the ultraviolet light-catalyzed (radical) reaction of hydrogen sulfide with polyisoprenes are monothiols and substituted pentamethylene sulfides, the latter derived by intramolecular abnormal addition. 4. The resemblance of the cyclic sulfides obtained by reaction of free sulfur with polyisoprenes to the products of polar hydrogen sulfide addition (as opposed to the products of the radical-type addition) supports the hypothesis that, in the sulfur-olefin reaction, the radical reaction chain is terminated by the capture of a hydrogen atom by an RS* radical, the thiol so formed adding intramolecularly in a polar reaction catalyzed by sulfur.