Hill, N. J. * •¥ Methyl iodide reaction at room temperature can be used to differentiate between mercaptan, sulfide, and disulfide sulfur in anhydrous systems? Mercaptans react slowly to give hydrogen iodide. Sulfides react ^QantitatiJ^ly in 1-3 days, but the product depends on the type of residue on the sulfur atom. Disulfides react very slowly; the sulfur-to-sulfur link is ruptured with liberation of free iodine. Mercuric iodide catalyzes the sulfide and disulfide reactions, making the former quantitative in 1 hour and the latter in 3 days. Pale crepe rubber or GR-S does not interfere chemically with the reactions. The reactions are presented here with a view to their use in the determination of the sulfur linkage in vulcanizates.
For many years the rubber chemist, in trying to explain the chemical nature of the vulcanization of rubber, was limited by two accepted theories: (1) Sulfur adds at the double bonds of the hydrocarbon, and (2) one atom of sulfur combines for each double bond saturated in the reaction. Therefore it was concluded that only one type of sulfur linkage would occur in vulcanizates. However, it was impossible on this basis to propose a hypothesis to account for all the facts. The few bits of direct evidence available have semed to support the theory of “one sulfur for each double bond saturated”. Since it is difficult to make any direct attack on this problem and since the art of vulcanization has far surpassed the science, it was not until 1938 that grave doubt was thrown on the generality of the “one sulfur atom per double bond saturated” theorem. The work of Brown and Hauser indicated that there were wide variations in the number of sulfur atoms combined for each double bond saturated, depending on the type of acceleration used. Four years later Thornhill and Smith pointed out that, in compounds containing reinforcing channel blacks, no loss of unsaturation could be detected on combination of sulfur during vulcanization. Thus the relation between sulfur combination and changes in unsaturation is at present obscure.
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