Zinc(II)-Catalyzed Disproportionation in Rubber: The mechanism of Sulfur Vulcanization Revisited
作者:Peter J. Nieuwenhuizen、Sandjai Timal、Jaap G. Haasnoot、Anthony L. Spek、Jan Reedijk
DOI:10.1002/chem.19970031117
日期:1997.11
AbstractModel studies have shown that cross‐link precursors, that is, intermediates in the sulfur vulcanization of rubber, are transformed into cross‐links by a nonsymmetric but regioselective disproportionation mechanism. Thus, two equivalents of the crosslink precursor of the type RSSX are transformed into XSX and the actual cross‐link RSSSR. Exchange of sulfur atoms is a prerequisite. A mechanism involving an SNi′ reaction with an allylic moiety, suggested in the literature, has not been observed. The disproportionation reaction is catalyzed by rubber‐soluble zinc‐dithiocarbamate complexes, an important class of vulcanization accelerators. By virtue of ligand‐functional‐group exchange reactions these complexes serve to transport and exchange sulfur atoms.