Isotopic Exchange of Free Sulfur with Thiurams, Isothiocyanates and Dithiocarbamates

Abstract

Abstract 1. Studies were made concerning the exchangeability, with elementary radioactive sulfur, of sulfur atoms in 15 compounds including thiurams, dithiocarbamate and isothiocyanates. The number of exchangeable sulfur atoms in each material was established, as well as the optimal conditions for exchange, and for seven of the compounds the activation energy for the process was determined. The exchange rate of thiurams, with elementary sulfur, increases with the number of sulfur atoms in the polysulfide chain. In tetramethyl-thiuram tetrasulfide the two middle sulfur atoms are more readily exchanged, while the outer four sulfurs, bonded to carbon, are exchanged less rapidly but not sufficiently so to allow carrying out a separate exchange. 2. The velocity of exchange is significantly reduced in the thiuram disulfides when aliphatic radicals are replaced by phenyl radicals. A difference in the influence of amino-group radical variations was noted between the thiurams and the dithiocarbamates. The results of the isotopic exchange of sulfur in these materials have been considered from the viewpoint of their effectiveness as accelerators in the vulcanization of rubber.