Syntheses, crystal structure and spectroscopic characterization of bis(dithiocarbimato)zinc(II) complexes: A new class of vulcanization accelerators

The compounds (Ph4P)2[Zn(RSO2N = CS2)2] [Ph4P+ = tetraphenylphosphanium cation; R = CH3 (1b), CH3CH2 (2b), CH3(CH2)3 (3b) and CH3(CH2)7 (4b)] were synthesized by the reaction of RSO2N = CS2K2·2H2O (1a–4a) with Zn(CH3COO)2·2H2O and Ph4PCl. The IR data were consistent with the formation of bis(dithiocarbimato)zinc(II) complexes. The NMR spectra showed the expected signals for the cation and the dithiocarbimate anionic complex in a 2:1 proportion. The compound 3b was also characterized by X-ray diffraction in the triclinic P 1 ¯ space group, with the Zn atom in a general crystallographic position, being coordinated by four sulfur atoms in a distorted tetrahedral coordination environment. The activity of compounds 1b–4b in the vulcanization of the natural rubber was evaluated and compared to the commercial accelerators CBS, MBTS and TMTD. These studies confirm that the bis(dithiocarbimato)zinc(II) complexes are new vulcanization accelerators, showing a similar degree of cure as MBTS, and scorch time values compatible with good processing safety for industrial applications.