Zinc dithiocarbamate

Chemical antiozonants comprise the second general class of commercial antiozonants. Of the many compounds reported to be chemical antiozonants, nearly all contain nitrogen. Compound classes include derivatives of l,2-dihydro-2,2,4-trimethylquinoline, A/-substituted ureas or thioureas, substituted pyrroles, and nickel or zinc dithiocarbamate salts (see also Antioxidants). The most effective antiozonants, however, are derivatives of -phenylenediamine... 

Zinc dithiocarbamates have been used for many years as antioxidants/antiabrasives in motor oils and as vulcanization accelerators in rubber. The crystal structure of bis[A, A-di- -propyldithio-carbamato]zinc shows identical coordination of the two zinc atoms by five sulfur donors in a trigonal-bipyramidal environment with a zinc-zinc distance of 3.786 A.5 5 The electrochemistry of a range of dialkylthiocarbamate zinc complexes was studied at platinum and mercury electrodes. An exchange reaction was observed with mercury of the electrode.556 Different structural types have been identified by variation of the nitrogen donor in the pyridine and N,N,N, N -tetra-methylenediamine adducts of bis[7V,7V-di- .vo-propyldithiocarbamato]zinc. The pyridine shows a 1 1 complex and the TMEDA gives an unusual bridging coordination mode.557 The anionic complexes of zinc tris( V, V-dialkyldithiocarbamates) can be synthesized and have been spectroscopically characterized.558... 

Toxicology. Zinc dithiocarbamates (ZDC) are contact allergens and are one of the chemical groups in rubber that cause the type IV delayed-type hypersensitivity skin reaction (DTH). ... 

Accelerator Thiuram Thiazole Thiuram Thiuram Zinc dithiocarbamate... 

The curative packages contained MgO 4 phr, ZnO 5 phr, stearic acid 2 phr, zinc dithiocarbamate 6 phr, sulfur 1 phr, and ethylene thiourea 1 phr... 

In the autoxidation of N-butylacetamide all the salicylaldimine chelates showed only inhibitory effects. We also found that two salicylaldimine chelates showed no significant catalytic properties and exhibited only inhibitory effects even in hydrocarbon autoxidation—viz., bis (N-butylsalicylaldimino) zinc and bis (N-butylsalicylaldimino) oxyvanadium-(IV). While there are some well known antioxidants containing zinc (e.g., zinc dialkythiophosphates or zinc dithiocarbamates), this is not a general property for zinc compounds. Zinc acetylacetonate, for example, had no inhibitory effect in the autoxidation of hydrocarbons or amides. 

Cure system species, accelerators and their reaction products This class of additive can present problems as they are often thermally labile, reactive and, in some cases, have a degree of ionic character (e.g. zinc dithiocarbamate salts). In these cases LC-MS is a more appropriate technique than GC-MS. It is also easier to use LC-MS with a number of the approved food simulants as they can be injected directly into the instrument, being compatible with the mobile phase. In some cases the reaction products (e.g. aniline from diphenyl guanidine, and benzothiazole from thiazole and sulphonamide accelerators) are stable and so GC and GC-MS can be used. Peroxides are popular curatives for food use rubbers and the stable, breakdown products of these can be easily detected by GC-MS. 

Reaction mechanism The formation of sulphur acids, which serve as the catalyst for ionic hydroperoxide decomposition, arises through the oxidation of zinc dithiocarbamates by hydroperoxides. Reaction sequence (4.52) [63] ... 

In addition, zinc dithiocarbamates also act as radical scavengers, whereas in the literature, the main emphasis is generally put on their capability to destroy hydroperoxides. Their areas of application are grease and engine oils. 

Zinc dithiocarbamate can be used in small quantities (0.25-0.75 phr) with zinc oxide cures used in heat resistant and improve compression set. 

Zinc dithiocarbamate fungicides and stabilizers Treating cellulose to make vulcanized fiber Phosphors... 

Octocure. [Tiatco] Zinc dithiocarbam-ates or mercaptobenzothiazoles accel-eratenrs fex latex and mbber. 

Many compounds have been reported in the literature to be chemical antiozonants, and nearly all contain nitrogen. Compound classes include derivatives of 2,2,4-trimethyl-l, 2-dihydroquinoline, N-substituted ureas or thioureas, substituted pyrroles, and nickel or zinc dithiocarbamate salts. The most effective antiozonants, however, are derivatives of p-phenylenediamine (p-PDA). The commercial materials are grouped into three classes N,N -dialkyl-p-PDAs, Nalkyl-N -ary 1-p-PDAs, and NX-diary 1-p-PI) As. The NX-dialkyl-p-PDAs (where the alkyl group may be 1-methylheptyl, l-ethyl-3-methylpentyl, 1,4-dimethylpentyl, or cyclohexyl) are the most effective in terms of their reactivity to ozone. These derivatives increase the critical stress required for the initiation of crack growth, and they also reduce the rate of crack growth significantly. The sec-alkyl group is most active, for reasons that are not yet completely clear. The drawbacks of these derivatives are ... 

Although Zineb displays a broad spectrum of effectiveness and considerable antimicrobial activity, it has not often been employed as a microbicide for the protection of materials. The stable Ziram (see Section 9.10.2) is the preferred zinc dithiocarbamate for that application. The disodium salt of ethylenebisdithio-carbamic acid (Nabam) is also available. 

It has been established that the cause of the high thermal stability of the indicated cured rubbers is the presence of zinc dithiocarbamates, which are formed from dithiocarbamic acid (one of the decomposition products of thiuram disulfide) and zinc oxide. 

Undoubtedly more important than the rate of decomposition of hydroperoxides is the type of product obtained. Table 5 lists the major products obtained by completely decomposing TBHP with various sulfur compounds. With nickel and zinc dithiocarbamates... 

On the other hand, dithiocarbamate nickel and zinc complexes are very effective light stabilizers for polyolefins. Using a combination of iron(pro-oxidant) and nickel or zinc (stabilizers) dithiocarbamates, it is possible to control the rate of photo-oxidative degradation very accurately [1931]. For long induction periods a combination of iron and nickel dithiocarbamates is recommended, whereas for shorter times it is more usual to combine iron and zinc dithiocarbamates [1932]. The combination of different metal ions decreases the induction period and increases the rate of photo-oxidation. At higher concentrations of stabilizing (Ni, Zn) dithiocarbamates, much longer lifetimes can be achieved. 

Vulcanization by sulfur alone is of little help as it is too slow. The vulcanizing systems currently used contain accelerators like thiuram sulfides (R2N-CS-S-S-CS-NR2), zinc dithiocarbamates [(R2N-CS-S)2Zn], thiourea (H2N-CS-NH2), or zinc benzothiazoles,... 

Eigure 271. Zinc dithiocarbamate complexes containing the benzothiazole-2-thiolate ligand. 

Figure 273 Anionic zinc dithiocarbamate complexes containing other dithiolate ligands.

---