Mechanism of Mill Breakdown and Vulcanization in the Presence of 2-Mercaptobenzothiazole

Abstract

Abstract The mechanism of the action of 2-mercaptobenzothiazole, MBT, one of the most commonly employed accelerators of vulcanization, remains unclear. L. Wistinghausen and B. A. Dogadkin and D. M. Pevzner (1951, unpublished) showed that MBT is consumed in vulcanization, but these authors, because of the crudity of their methods, did not obtain quantitative relationships. In the present work there has been employed a preparation of the MBT which was tagged in the thiazole ring by the radioisotope S35. The synthesis of this compound was carried out in the following manner. MBT, tagged in both of its sulfur atoms, was first synthesized from phenyl isothiocyanate and elementary S35. The resulting MBT was then heated in a sealed ampule with an excess of inactive elementary sulfur for six hours at a temperature of 140°. Under these conditions the exchange reaction between the elementary sulfur and the sulfur of the mercapto group of the MBT reaches equilibrium. The activity of the resulting MBT fell to one-half of the original value. In this way the benzothiazole radical was tagged, by the introduction into the molecule of MBT of the radio-isotope S35 which does not exchange with elementary sulfur, under the conditions of vulcanization, and it thus became possible to measure simultaneously the velocity of the addition of the sulfur and the velocity of addition of the accelerator to the rubber.