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Zinc(II)‐Catalyzed Disproportionation in Rubber: The mechanism of Sulfur Vulcanization Revisited
Author(s) -
Nieuwenhuizen Peter J.,
Timal Sandjai,
Haasnoot Jaap G.,
Spek Anthony L.,
Reedijk Jan
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970031117
Subject(s) - disproportionation , dithiocarbamate , vulcanization , chemistry , moiety , sulfur , catalysis , allylic rearrangement , zinc , polymer chemistry , reaction mechanism , natural rubber , medicinal chemistry , organic chemistry
Model 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 S N i′ 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.