Tetramethylthiuram Disulfide Vulcanization of Extracted Rubber. II. Structure of Radioactive Tetramethylthiuram Disulfide

Abstract

Abstract Tetra-substituted thiuram polysulfides are notable because of their action as “accelerators” in rubber vulcanization and also because of their ability to vulcanize rubber without added sulfur, especially in the presence of zinc oxide, which leads to the formation of zinc dimethyldithiocarbamate (ZnDMDC) and other substances. A study of the structure of tetramethylthiuram disulfide (TMTD) is reported in this paper. This has involved the introduction of radioactive sulfur. A corollary has been the similar study of ZnDMDC, which is an “accelerator” but not a vulcanizing agent. The synthesis of radioactive TMTD (i.e., TMTD*) was accomplished by heating 4.16 grams (0.02 mole) of tetramethylthiuram monosulfide (TMTM) and 1.28 grams (0.04 atom) of radiosulfur (S*8) to 120° in a stream of nitrogen for 30 minutes. By extraction with hot alcohol and benzene, a series of crystalline fractions was secured which totaled 3.38 grams, a yield of 70 per cent. This material melted at 150–156° C, with decomposition. The excess S*8 was recovered in a second experiment. Pyrolysis of the TMTD* prepared in the above manner was carried out at 160–230° C in a modified Claisen flask. There were produced S8*, tetramethylthiourea*, and CS2* in nearly theoretical yield. The radioactivities of the thiuram disulfide and of the pyrolysis products (the CS2* being converted to phenylhydrazinium phenyldithiocarbazate* or to 1-phenylthiosemicarbazide* for study), which are recorded in Table I, show that the tracer sulfur atoms distributed themselves uniformly throughout the various molecules.