Dithiocarbamates, oxidation

The calculated potential are, respectively 26 mV and -260 mV for 10 mol/L DDTC at pH = 4.7, which are not consistent with the flotation beginning potential in Fig. 4.21. On the other hand, the reaction of dithiocarbamate oxidation to thiouram disulphide can be written as... 

In very recent work, Lieder (165) calculated standard potentials of the dithiocarbamate-thiuram disulfide redox system via thermochemical cycles and computational electrochemistry. A pathway proceeding via a single electron detachment is predicted to be the most favorable mechanism for dithiocarbamate oxidation, while thiuram disulfide reduction can proceed via two pathways. In the gas phase, reduction followed by sulfur-sulfur bond cleavage is energetically preferred, while in solution a concerted bond-breaking electron-transfer mechanism is predicted to be equally probable. 

NOBF4 revealed ions associated with the species [Co2(S2CNR2)5S] and [Co2(S2CNR2)5S2]. Neither the nature of sulfur coordination nor its source is known, although the authors suggest that the latter is the result of oxidation of thiuram disulfide (generated by dithiocarbamate oxidation) by NO (303). 

The reaction with sodium sulfite or bisulfite (5,11) to yield sodium-P-sulfopropionamide [19298-89-6] (C3H7N04S-Na) is very useful since it can be used as a scavenger for acrylamide monomer. The reaction proceeds very rapidly even at room temperature, and the product has low toxicity. Reactions with phosphines and phosphine oxides have been studied (12), and the products are potentially useful because of thek fire retardant properties. Reactions with sulfide and dithiocarbamates proceed readily but have no appHcations (5). However, the reaction with mercaptide ions has been used for analytical purposes (13)). Water reacts with the amide group (5) to form hydrolysis products, and other hydroxy compounds, such as alcohols and phenols, react readily to form ether compounds. Primary aUphatic alcohols are the most reactive and the reactions are compHcated by partial hydrolysis of the amide groups by any water present. 

The next significant strength improvement followed the 1950 Du Pont (19) discovery of monoamine and quaternary ammonium modifiers, which, when added to the viscose, prolonged the life of the ziac cellulose xanthate gel, and enabled even higher stretch levels to be used. Modifiers have proliferated siace they were first patented and the Hst now iacludes many poly(alkylene oxide) derivatives (20), polyhydroxypolyamines (21—23), and dithiocarbamates (24). 

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

Properties of zinc salts of inorganic and organic salts are Hsted in Table 1 with other commercially important zinc chemicals. In the dithiocarbamates, 2-mercaptobenzothiazole, and formaldehyde sulfoxylate, zinc is covalendy bound to sulfur. In compounds such as the oxide, borate, and sihcate, the covalent bonds with oxygen are very stable. Zinc—carbon bonds occur in diorganozinc compounds, eg, diethjizinc [557-20-0]. Such compounds were much used in organic synthesis prior to the development of the more convenient Grignard route (see Grignard reactions). 

EDA reacts readily with two moles of CS2 in aqueous sodium hydroxide to form the bis sodium dithiocarbamate. When aqueous ammonia and 2inc oxide (or manganese oxide or its hydrate) is used with a basic catalyst, the 2inc (or manganese) dithiocarbamate salt is isolated. Alternatively, the disodium salt can react with ZnSO or MnSO followed by dehydration in an organic solvent to yield the same salts (48—50). 

The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator. 

AuCl3(tht) [129], AuX3[S(benzyl)2)2] (X = Cl, Br) [130] and AuC13 (thian-threne). Various dithiocarbamates and dithiolene complexes have been made, some by oxidation of gold(I) complexes (Figure 4.26). 

Dithiocarbamates of transition group elements in unusual oxidation states. J. Willemse, J. A. Cras, J. J, Steggerda and C. P. Keijzers, Struct. Bonding (Berlin), 1976, 28, 83-126 (195). 

The utility of thallium(III) salts as oxidants for nonaromatic unsaturated systems is a consequence of the thermal and solvolytic instability of mono-alkylthallium(III) compounds, which in turn is apparently dependent on two major factors, namely, the nature of the associated anion and the structure of the alkyl group. Compounds in which the anion is a good bidentate ligand are moderately stable, for example, alkylthallium dicar-boxylates 74, 75) or bis dithiocarbamates (76). Alkylthallium dihalides, on the other hand, are extremely unstable and generally decompose instantly. Methylthallium diacetate, for example, can readily be prepared by the exchange reaction shown in Eq. (11) it is reasonably stable in the solid state, but decomposes slowly in solution and rapidly on being heated [Eq. (23)]. Treatment with chloride ion results in the immediate formation of methyl chloride and thallium(I) chloride [Eq. (24)] (55). These facts can be accommodated on the basis that the dicarboxylates are dimeric while the... 

Dithiocarbamates of Transition Group Elements in Unusual Oxidation States... 

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