The First Theoretical and Experimental Proof of Polythiocarbamatozinc(II) Complexes, Catalysts for Sulfur Vulcanization

Abstract

The existence of polythiocarbamatozinc complexes, species presumed to be involved in catalyzing sulfur vulcanization, has been studied by computational and mass-spectrometric techniques. Density functional calculations reveal that the sulfuration energy of bis(trithiocarbamato)zinc(ii) is comparable to that of bis(phenyltrithiolato)-zinc(ii), a stable sulfurated complex. Interestingly, the analogous nonsymmetrically sulfurated complex (dithiocarbamato)(tetrathiocarbamato)zinc(ii) is energetically slightly more favorable. The calculations indicate that polythiocarbamatozinc complexes may indeed be involved in the sulfur vulcanization cascade, a conclusion corroborated by ensuing laser-desorption ionization (LDI) mass-spectrometric measurements on mixtures of dithiocarbamatozinc(ii) complexes and elemental sulfur. These demonstrate the presence of polythiocarbamatozinc ions that are sulfurated with up to eight additional sulfur atoms.

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

“…Clear evidence for the existence of such exchange reactions is provided by the experimental studies of R-S x -R compounds with radioactively labeled sulfur, where R is an alkyl or aryl group. 67,68,69 Specifically, the studies involved exchange reactions between 35 S-labeled disulfide with trisulfides and of 35 Slabeled trisulfides with tetrasulfides, which are summarized below where the fraction of radioactively labeled compound is indicated by 1* or 1/2* or 1/3*. The C-S bond in R-S x -R is unreactive, but the S-S bonds are quite labile, taking part in sulfur-exchange reactions.…”

“…These macromolecular complexes can be either internally chelated, as in dimethyl dithiocarbamate (VII) or may form a benzothiazolezinc-complex like (VIII). 2,3,5,[10][11][12]69 (VII) (VIII) None of these structures have appreciable solubility in rubber or significant reactivity towards sulfur. However, the solubility and reactivity are enhanced if the zinc coordinates with an amine that is released from the sulfenamide or with carboxylate ligands, which are present in systems with stearic acid.…”

Vulcanization of chlorobutyl rubber. III. Reaction mechanisms in compounds containing combinations of zinc dimethyldithiocarbamate, tetramethylthiuram disulfide, sulfur, and ZnO

“…6,13,20 Such sulfur-rich zinc (II) com- plexes have not been isolated though evidence for sulfur-rich zinc (II) complexes has been demonstrated in theoretical Density Functional calculations and mass spectroscopic analysis of Zn 2 (dmtc) 4 /sulfur. 21 Thiuram pendent groups that are proposed to result from the reaction of sulfur-rich zinc (II) complexes with the polymer have not been detected in model compound studies of Zn 2 (dmtc) 4 accelerated systems. 13,22,23 Geyser and McGill 23 proposed that polysulfidic thiuram pendent groups did form, but crosslinked immediately in the presence of Zn 2 (dmtc) 4 that catalyzed their crosslinking.…”

Syntheses and Characterization of Novel Organometallic Tin (Iv) Complexes With Dithiocarbimates and Their Action as Accelerators in the Nitrile Rubber Vulcanization

“…Possívelmente, como no caso dos ditiocarbamatos, na presença de S 8 ocorre a formação de ditiocarbimatos ricos em enxofre com posterior transferência desses átomos para a formação das ligações cruzadas. 8,9 Essa possibilidade é corroborada pelo fato de já terem sido isolados complexos de ditiocarbimatos ricos em enxofre. 10 Foi verificado, ainda, que vários complexos de metais com ditiocarbimatos derivados de sulfonamidas de fórmulas gerais: (Ph 4 P) 2 7 ] também têm ação aceleradora na vulcanização da NR.…”