Reaction of sulfur, hydrogen sulfide, and accelerators with propylene and butadiene

Abstract

As part of a stud y o f vulcani zat ion, propylene as a model compound for natural r ubber has been reacted with sulfur alo ne, with hydrogen sulfide alone, a nd with each of t hese materials in t he prese nce of certain accelerators. Butadiene as a model compound for intermediate conj ugated systems found in vulca ni7-ed rubber by mea ns of infra red st udies has been similarly st udied. R esults of mass spectrometer analyses of t he volatile portions of t he reaction products indicate the formation of s ulfides, dis ulfides, and carbon-t o-carbon bon ds. Zin c dimethyl dithiocarbamat e (ZnDMDC), a vulcanization accelerator, faci litates t he formation of hydrogen sulfide from the olefin or diolefin in the prese nce of s u lfur, and in t urn promotes the reaction of h yd roge n sulfide with the olefin and diolefin. The ZnDMDC-accelerated r eaction of hydroge n s ulfide and s ulfur with the diolefin mav account for the reduced conj ugation observed in vulcanizates accelerated with ZnD MUC. Studi es with fr ee ra dical a ccelerators show that a m echani s m other than a free radical chain mechanism is invol ved in the formation of diisopropyl sulfide in the reaction of propyle ne with s ulfu r (or hydroD'en sulfidc) a nd certa in substances t hat facilitate t he reactions. The s ame co nclusion applies to the formation of a nonvolatile residu e in t he ZnD MDC-accelerated rea ction betwee n propyle ne a nd s ulfur. Other p hases of the reactions involve the format io ll of compounds from what ap pear to be f ree radical fragm ents of the origin al m olecule. In mos t of t he r eactions, appreciable portions of the reaction products are nonvolat ile.