Thiuram disulfide oxidation

Curing Systems. Polychloroprene can be cured with many combiaations of metallic oxides, organic accelerators, and retarders (114). The G family of polymers, containing residual thiuram disulfide, can be cured with metallic oxides alone, although certain properties, for example compression set, can be enhanced by addition of an organic accelerator. The W, T, and xanthate modified families require addition of an organic accelerator, often ia combination with a cure retarder, for practical cures. 

All compositions contain EPDM, 100 phr zinc oxide, 5 phr stearic acid, 1 phr antioxidant, 1 phr 2-mercaptobenzothiazole (accelerator), 1.5 phr tetramethyl thiuram disulfide (accelerator), 1 phr and sulfur, 1.5 phr. 

In dithiocarbamato complexes such an ambiguity can only occur when at least two dithiocarbamato ligands are bonded to a metal. In that case the question arises whether the compound is a bis (dithiocarbamato) or a thiuram disulfide complex. In these two types of complexes the oxidation number of the metal differs 2 units. 

The MofVJ compounds [Mo(R2cffc)4]X can be prepared by oxidative addition of thiuram disulfide to molybdenum carbonyls or by mild oxidation of Mo(R2C fc)4. 

Oxidation of these complexes with halogen results in the oxidation of the ligand, yielding a thiuram disulfide complex X2M(R4tds), leaving the oxidation state of the metal unchanged (99,100,161). 

Since isolable organocopper) 11) compounds do not apparently exist, it is rather surprising that oxidation of the cuprate CdI+[(CF3)2Cu ] (prepared in situ) with thiuram disulfide affords (CF3)2Cu "S2CNEt2 (see Eqn. 1 in Scheme 1.6), the first and so far only example of an organocopper compound with the copper atom in the trivalent oxidation state. The structure of this compound was unambiguously proven by an X-ray crystal structure determination (see Fig. 1.2) [37]. 

When these experiments were repeated, in the absence of air, it was discovered that the intensity of the ESR signal due to the Ag11 species almost doubled.539 Reexamination of the reaction for R = Bun showed that further oxidation to a red, diamagnetic Ag complex occurred in air or with excess thiuram disulfide and this accounted for the decrease in signal intensity.540 Values of spin Hamiltonian parameters for some silver(II) complexes are given in Table 67.539-542... 

A kinetic study of the oxidation of some hexameric silver(I) dialkyl dithiocarbamate complexes by thiuram disulfides to the silver(II) complexes has been reported.543 Although a 100-fold excess of the thiuram disulfide was used, the formation of the Ag111 complex reported earlier was not considered. 

I) Simple Monomeric Molybdenum Complexes. The first report on the synthesis of simple Mo dithio complexes appeared in 1971 when Mo(IV)(R2Dtc)4 complexes were obtained by CS2 insertion into Mo(NR2)4 complexes (68). Shortly after this report, the synthesis of these complexes from MoC14 and NaR2Dtc in acetonitrile was reported (88). A variety of tetrakis R2Dtc complexes of Mo(IV) also were obtained by the oxidative decarbonyla-tion of Mo(CO)6 with tetraalkyl thiuram disulfide (481,482, 609). 

Reverse reactions, in which the disulfides are reduced and S—S bond breaking takes place, are also possible. So thiuram disulfide reacts with elemental Cu or Ag yielding the metal dithiocarbamates, and (109) can be oxidized with thiuram disulfide to (110) and (111) to (112). 

The complexes of thiuram disulfide can be oxidized by an excess of halogens to products containing the bis(iminio)trithiolane dication (113).122 123 One of the sulfur atoms is removed as free sulfur or as sulfur halide. According to some reports the bis(iminio)tetrathiolane dication (114) also exists.124 In our investigations, however, we could not obtain any proof of this ion. The electrochemical literature about the oxidation of thiuram disulfide is also contradictory.125,126 Apart from the trithiolane ion a dithietane ion (115) is prepared by oxidation of dimethylformamide with bromine.127 As far as we know, no other disulfide can be oxidized to an analogous dication. 

The ion (113) is an oxidant in several reactions.128 In addition to the normal thiuram disulfides, isothiuram disulfide (116) also exists.129 However, no complexes are known in either a neutral or (for R = H) a deprotonated form. Numerous other ring systems exist in which a CS2 fragment is incorporated, e.g. rhodanines and thiazoles.1 They can act as neutral ligands in coordination compounds. 

The system Cl-butyl-cis-polybutadiene has been studied in some detail because it was suitable for the developed differential swelling technique and because this system of blends vulcanized with zinc oxide, sulfur, and thiuram disulfide first revealed the presence of interfacial bonds. This curative system has the feature of a flat cure —i.e.y the two homophases are vulcanized rapidly, and the crosslinked density does not increase radically as vulcanization time is prolonged. This is observed in Table IV by swelling and extractable levels of a series of crosslinked networks cured at increasing times and swollen in a common solvent, cyclohexane. 

On oxidation of aqueous solutions by H202, Cl2, or S20 thiuram disulfides, of which the tetramethyl is the commonest, are obtained ... 

Thiuram disulfides, which are strong oxidants, are also used as polymerization initiators (for, when heated, they give radicals) and as vulcanization accelerators. 

Dithiocarbamate and dithiophosphinate complexes have important uses. The former are used as fungicides and for solvent extraction and the latter as high pressure lubricants. Dithiocarbamates stabilize high oxidation states as in [FeIV(dtc)3]+ or [NiIV(dtc)3]+. Although dithiocarbamates are usually made from sodium salts such as NaS2CNMe2 or by oxidations using thiuram disulfides, they can also be made by insertion reactions of CS2 with dialkylamides, for example,... 

The kinetics of oxidation of dithiocarbamate anions to thiuram disulfides in 30% aqueous acetone by [Mo(CN)g] , [W(CN)g] , and 10 other substitution-inert metal complexes have also been investigated 61). Dithiocarbamates decompose in acid solution and oxidations were consequently performed only on the anionic forms in the pH range 9-12, at which no change in rate constants was observed. The only exception was that of thiophenol, which, upon reacting with [Mo(CN)g] , showed that the reaction rate contribution due to oxidation of the PhSH form was less than 0.002% that of PhS . All of the dithiocarbamates obeyed a simple second-order rate law. 

Henderson, et al., 1995). The reaction mechanism for the thiuram disulfide class of oxidizing agents and maleimide class of alkylating agents were examined in our laboratory and are presented below. Thiuram disulfides (Fig. 2, for structures) were examined in detail, since a member of this class... 

In conclusion, thiuram disulfides are examples of a class of compounds that oxidize retroviral NC proteins and hold promise in antiretroviral therapy. 

Tetraalkylthiuram disulfides, R2NC(S)S-S(S)CNR2, are oxidized forms of the di-alkyldithiocarbamate ions R2NC(S)Sa Thiuram disulfides possess pronounced oxidative properties and can easily oxidize and stabilize polyvalent cations in high oxidation states (Ni(III), Cu(III), Ag(II), etc.) as well as coordinate these metal ions in the molecular form [18,19]. Therefore, it should always be kept in mind that complexation of polyvalent cations with dialkyldithiocarbamate anions can be accompanied by a redox equilibrium of the following type ... 

These are easily prepared by the reaction of amines with carbon disulfide (1) in the presence of alkali (Scheme 17).2 The synthesis of dithiocarba mates (4) was first reported by Debus in 1850. Dithiocarba mates (4) form metal chelates, and sodium dimethyl dithiocarbamate is used in quantitative inorganic analysis for the estimation of metals, e.g. copper and zinc. Dithiocarba mates are also employed as vulcanisation accelerators and antioxidants in the rubber industry, and as agricultural fungicides.3 The parent dithiocarbamic acids are unstable, decomposing to thiocyanic acid and hydrogen sulfide however, the salts and esters are stable compounds. Dithiocarba mates (4) are oxidised by mild oxidants to the thiuram disulfides (38) (Scheme 17). 

Accelerators, e.g. zinc oxide and fatty acids, increase the rate of vulcanisation of rubber by sulfur and they reduce the amount of sulfur required from 10% to <3%. Certain sulfur-donating accelerators, like thiuram disulfides (1) and mercaptobenzothiazole (2), will effect vulcanisation without added sulfur to yield products with greatly enhanced ageing properties.1... 

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