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Efficient sulfur vulcanizing systems based on thiazolesulfenamide accelerators derived from secondary amines show unusual and complex vulcanization kinetics in NR. This feature does not appear to have been reported previously. Depending on the nature and purity of the accelerator, the ratio of accelerator to sulfur, the cure temperature, the type of rubber being used, and the presence of other additives, two distinct periods of crosslinking may be evident, separated by a more or less well-defined plateau. This plateau is longer and more distinct if the accelerator is pure, its ratio to sulfur is high, the cure temperature is low, and there are no other additives present. Sulfenamide accelerators derived from both primary and secondary amines may give rise to this behavior in rubbers other than NR. The observed behavior has been shown to be due to the formation, during the first cure period, of an extractable crosslinking inhibitor. The structure of this inhibitor is still in doubt, but the present balance of evidence favors it being an aminodithiobenzothiazole [Structure (1)] or a dithiobisdialkylamine [Structure (2)] or a polythio variant of those structures.

Monoaquobis(ethy1enediamine) (pyridylmethyl)chromium(lll) complexes, 2-NC5H4CH2Cr(en)2(H20)2+ and 3-NC5H,CH2Cr(en)2(Ha20)2+, are prepared by the reduction of the corresponding picolyl chlorides by the c ~I I ( e n ) ~~+ ion. The decomposition of these ions is studied in 0.01 -1 .OM-perchloric acid and in acetate buffers of pH 1-7.Spectral changes show that these complexes undergo aquation before carbon-chromium bond cleavage. Product studies as well as kinetic data and activation parameters obtained indicate that the 2and 3-ions decompose via the penta-aquo-derivative. 2-NC,H,CH,Cr(H,O) 62+, and the trisaquo-derivative, 3-NC,H,CH,Cr(en) (H20)32+ respectively. Acetate-ion catalysis is also observed for the decomposition of these ions.