Zinc Sulfur Research Articles

Study of curative interactions in cis‐1,4‐polyisoprene. XII. The cis‐1,4‐polyisoprene–sulfur–tetramethylthiuram disulphide–ZnO–stearic acid vulcanization system

AbstractSeveral aspects on the mechanism of vulcanization in the synthetic cis‐1,4‐polyisoprene (IR)‐sulfur‐tetramethylthiuram disulphide (TMTD)–ZnO system were harmonized. The differential scanning calorimetry (DSC) thermograms showed that the vulcanization processes became better resolved on increasing the curative loading in the compound. Two major crosslinking reactions occurred consecutively in the IR (100)–sulfur (9.46)–TMTD (8.86)–ZnO (3.00) mixture, viz the IR–sulfur–TMTD–ZnO and IR–sulfur–zinc dimethyldithiocarbamate (ZDMC) (or IR–sulfur–ZDMC–ZnO) reactions. In the first process poly‐and disulfidic pendent groups RSxSX (R = polyisoprenyl, X = Me2NC (S), x ≥ 1) formed via the IR–XSSxSX reaction, and in the second via the IR–XSSxZnSSX reaction. Thermogravimetric analysis (TGA) and high‐pressure liquid chromatography (HPLC) data showed that dimethyldithiocarbamic acid liberated during the IR–sulfur–TMTD–ZnO reaction was trapped by ZnO to yield ZDMC. Hence ZDMC was a product, and not precursor, of this crosslinking process. A comparison of reactions in IR–sulfur–TMTD–ZnO and poly(ethylene‐co‐propylene)–sulfur–TMTD–ZnO mixtures showed that the participation of IR molecules was essential for ZDMC formation. The ZDMC concentration remained constant at ∼ 38.4 mol % during the later stages of cure, showing that it did not participate in the desulfuration reactions of polysulfidic links. In the presence of stearic acid the stearic acid–ZnO reaction occurred at 87°C as was manifested by an intense crystallization peak of zinc stearate. The vulcanization processes were the same both in the presence and absence of stearic acid.

Study of curative interactions in cis‐1,4‐polyisoprene. XI. Network maturing reactions in the cis‐1,4‐polyisoprene–sulfur–zinc dimethyldithiocarbamate and cis‐1,4‐polyisoprene–sulfur–zinc dimethyldithiocarbamate–ZnO systems

AbstractThe network maturing reactions of the inefficient cis‐1,4‐polyisoprene (IR)–sulfur–zinc dimethyldithiocarbamate (ZDMC) and IR–sulfur–ZDMC–ZnO vulcanization systems were discussed. The Moore–Trego efficiency E was exceptionally high and increased, for example, from 13.0 at 132.4°C to 49.9 at 170.0°C in the IR–sulfur–ZDMC mixture. Calculations showed that ∼ 60% of the elemental sulfur was combined in the network in the form of cyclic sulfides and/or vicinal crosslinks at 148.2°C. The inefficient use of sulfur at the initial cure stages may be attributed to the insolubility of ZDMC in rubber. The increase in E at the later stages of vulcanization was attributed to a decrease in the total number of polysulfidic crosslinks, as the number of mono‐ and/or disulfidic crosslinks remained constant. The destruction of polysulfidic crosslinks was enhanced in the absence of ZnO, due to the catastrophic attack of thiophilic species such as Me2NH. The Me2NH resulted from the rapid decomposition of dimethyldithiocarbamic acid, which formed as a by‐product in the initial crosslink reactions. No evidence was found for the participation of ZDMC in crosslink desulfuration. ZDMC is not a vulcanizing agent.

Synthesis and structure of bridged twelve-membered silver–zinc–sulfur cyclic compound: a combination of hard and soft Lewis acidic and basic centres

The reaction of silver trifluoromethanesulfonate 2 with zinc bis[bis(trimethylsilyl)amide]4 and 2,4,6-triisopropylbenzenethiol 5 in a 4 : 4 : 6 ratio yields the mixed metal thiolate complex 3 with a twelve-membered silver–zinc–sulfur ring bridged by two trifluoromethanesulfonate anions; compound 3 is remarkably stable in solution.

Synthesis and Tribofragmentation of Monothio-Phosphates

Abstract Besides the well-known zinc dithiophosphates (ZDTP) phosphorus and sulfur containing ashless additives are used to improve the lubrication properties of modern engine and hydraulic oils. It is generally accepted that a wear reducing reaction layer is formed by additive tribofragmen-tation reactions in the friction zone of the metal surface. The composition of those reaction layers and the formation mechanism relative to the used additive is quite unknown. By systematic modification of monothiophosphates the influence of molecule parameters on the wear reducing properties were investigated (1).

Reactions of trifluoromethyl bromide and related halides: part 10. Perfluoroalkylation of aromatic compounds induced by sulphur dioxide radical anion precursors

Perfluoroalkylation of electron-rich aromatic compounds with trifluoromethyl bromide, or long-chain perfluoroalkyl iodides, was performed in the presence of sodium dithionite or zinc–sulphur dioxide. This alkylation occurred at the ortho and para positions relative to the amino or hydroxy substituent. Pyrroles were perfluoroalkylated regioselectively at the 2-position. This alkylation was interpreted as a radical aromatic substitution; the formation of the perfluoroalkyl radical can be induced by a single-electron transfer from sulphur dioxide radical anion to the perfluoroalkyl halide.

Crosslinking of poly(vinyl chloride) with metal oxides, sulfur, and organo sulfur compounds

AbstractThe crosslinking of poly(vinyl chloride) in the presence of zinc oxide, magnesium oxide, ethylenethiourea (ETU), tetramethylthiuramdisulfide (TMTD), and sulfur at 160 and 180°C has been studied. The effects of ETU and sulfur on the crosslinking of PVC in the presence of TMTD have been individually studied. It has been found that zinc dimethyldivhiocarbamate (ZnDMDC) is the actual crosslinking agent and heat stabilizer of PVC, formed in the cured polymer mix.

Direct determination of zinc, lead, iron and total sulphur in zinc ore concentrates by X-ray fluorescence spectrometry

A direct X-ray fluorescence (XRF) method has been developed for the rapid determination of zinc, lead, iron and total sulphur present in zinc ore concentrates. The concentrations of the elements present, mainly as sphalerite, galena, pyrite and pyrrhotite, vary widely: Zn, 40–65; Pb, 0.1–10; Fe, 0.5–11; and S, 25–33%m/m. Using a wavelength-dispersive X-ray spectrometer and samples prepared as briquettes, Zn and Pb may be determined directly using the Kβ and Lγ1 lines, respectively. For Zn, a mathematical model (concentration-based correction equation) was applied to correct for inter-element effects. For the determination of Fe the ratio of the fluorescence intensities of the Fe Kα and Zn Kβ lines was used and, for the determination of total S, the intensity of the S Kα line was corrected with the Rayleigh scatter tube line, Rh Lα. For both iron and total sulphur, subsequent application of the mathematical model helped to correct for the residual inter-element effects. Good agreement was obtained between experimental and certified values for two international reference materials.

High-performance liquid chromatography-inductively coupled plasma profiles of cadmium, zinc, sulphur and other elements in rat liver supernatants after cadmium injection

The distribution of cadmium zinc sulphur and other elements in the liver supernatants of rats and their variation with time following a single intraperitoneal injection of cadmium chloride were characterized by high-performance liquid chromatography (HLPC) coupled with an inductively coupled plasma. Cadmium that was bound to high-molecular-weight-proteins before the induction of metallothionein was analysed more easily using an Asahipak GS-520 column whereas the distributions of other elements and of cadmium bound to metallothionein were better characterized on a TSK G3000SW column. Cadmium bound primarily to a distinct high molecular-weight protein before the induction of metallothionein. After the injection its distribution shifted with time to metallothionein. An atomic emission spectrometer employing an inductively coupled argon plasma and a vacuum UV monochromator was effectively used as a multi-element specific detector for HPLC.

Zinc–sulphur bond enthalpy: its determination in the compound bis(diethyldithiocarbamato)zinc(II)

The standard enthalpy of formation of bis(diethyldithiocarbamato)zinc(II), as well as that of the salt diethylammonium chloride, has been determined by solution calorimetry at 298.15 K, giving –(289.65 ± 4.9) and –(359.63 ± 1.22) kJ mol–1, respectively. From the standard enthalpy of formation of the chelare, the enthalpy of formation in the gaseous phase, ΔHf⊖[Zn(S2CNEt2)2,g]=–(147.0 ± 5.0) kJ mol–1 was derived. The homolytic and heterolytic zinc–sulphur bond enthalpy parameters were calculated to be 177.4 ± 3.5 and 740.2 ± 3.5 kJ mol–1, respectively. These values are discussed and appear to correlate with the zinc–sulphur bond distance.

Effect of Mixing Conditions on Irritant Potency of Zinc Oxide and Sulfur Dioxide

Effect of Mixing Conditions on Irritant Potency of Zinc Oxide and Sulfur Dioxide

Polymerization of olefin oxides with zinc n‐butyl xanthate and zinc dimethyldithiocarbamate catalysts: Mechanism of initiation

AbstractXanthates and dithiocarbamates of metals have been reported to be effective as catalysts for the polymerization of olefin oxides. To investigate the mechanism of initiation, the bulk polymerization at 50°C of 1,2‐butene oxide with zinc n‐butyl xanthate (ZBX) at a monomer: ZBX molar ratio of 584: 1 was studied by ultraviolet and infrared spectroscopy. There is a rapid conversion of the sulfur–zinc bond in the metal xanthate to a structure magnified image containing sulfur–carbon and oxygen–zinc bonds, the latter acting as the site of the propagation step during polymerization. The xanthate ester moiety is subsequently converted to the oxygenated analogs, namely, O,O‐dialkylthiocarbonate and dialkyl carbonate. These changes are independent of the propagation step. The changes observed in the polymerization of butene oxide with zinc dimethyldithiocarbamate are similar, but much slower than in the case of ZBX. The presence of the carbonate ester moiety was also shown in the benzene‐insoluble, catalytically active fraction isolated from seeded catalyst, i.e., from the reaction product of propylene oxide and ZBX at a molar ratio of 8:1 or lower. This fraction also contained ionic sulfur.

Mercaptobenzothiazole Vulcanization Using Sulfur35

Abstract A study has been made of the function of raercaptobenzothiazole in the vulcanization process. Radioactive sulfur35 and mercaptobenzothiazole tagged with sulfur35 were used for measuring the sulfur and mercaptobenzothiazole reaction rates. The effects of variations in the zinc oxide, sulfur, and mercaptobenzothiazole concentration on the sulfur combining rates were determined. It was found that a marked induction period exists, during which the zinc mercaptide of mercaptobenzothiazole, the initial product, reacts readily with sulfur. The ratio of combined sulfur to consumed mercaptobenzothiazole is constant during the vulcanization process. A kinetic expression is given which accounts for the data. When polyisobutylene was substituted for GR-S or Hevea, the zinc mercaptide of mercaptobenzothiazole was found to be the initial product. A mechanism is postulated for the accelerating properties of mercaptobenzothiazole. It involves the formation of the zinc mercaptide, which reacts with sulfur and rubber to regenerate mercaptobenzothiazole and form sulfur-rubber compounds.