Thiocarbamates with zinc

Uses Zineb is a light-colored powder or crystal. It is a polymer of ethylene (bis) thiocarbamate units linked with zinc. Zineb is used to prevent crop damage in the field and to protect harvested crops from deterioration during storage or transport. It was used to protect fruit and vegetable crops from a wide range of foliar and other diseases. It was available in the United States as wettable powder and dust formulations. Zineb can be formed by combining nabam and zinc sulfate in a spray tank.7121319... 

Nitrogen-containing modifiers such as DMA, discussed by Deshmukh [196], are generally ineffective without zinc in the spin-bath. It is known that DMA reacts with carbon disulfide in viscose to form dimethyldithiocarbamate (Equation 10.16), which is an effective agent in modifying viscose. The mechanism by which cellulose xanthate decomposition is retarded is believed to involve association of the thiocarbamate with the xanthate group by a bridging zinc atom (Equation 10.17). 

The dithiocarbamates include zinc dibutyldi-thiocarbamate (ZDBC), zinc diethyldithiocarbamate (ZDEC) and zinc dimethyldithiocarbamate (ZDMC). In the rubber industry, the carbamates are principally used in gloves, condoms and elastic bands. Due to their chemical similarity with thiurams, the potential for cross-reactivity between these groups exists (Con-de-Salazar 1990a Knudsen and Menne 1996). The greatest use of carbamates is not in rubber but in pesticides and fungicides (Table 8). 

Zinc carbamate complexes are well known, and the structural types and stabilities can be compared with thiocarbamates and dithiocarbamates which are discussed in Sections 6.8.11.1.3 and 6.8.7.1.4482 Carbamates of zinc can be formed from the reaction of carbon dioxide with alkylzinc alkyl amides and further reaction with alkylzinc can give a distorted cubane structure.483 The tetrameric diethylcarbamate species initially formed can also be used to produce monomeric or dimeric carbamate structures in reaction with amines tetramethylethylenediamine forms a monomer [(Me2NCH2)2Zn(02CN(C2H5)2)2] with an octahedral zinc center and pyridine forms a dimer[CsH5NZn2Me(02CN(C2H5)2)3] with tetrahedral zinc centers.484... 

Alkylzinc thio- and selenocarbamate derivatives are coimnonly air-sensitive white crystalline solids, with the thiocarbamate derivatives being more soluble in organic solvents than the selenocarbamate derivatives. They have been found to be dimers of general formula [RZnE2CNRy2, in which each carbamate chelates one metal atom and bridges to the next one (Figure 41). The zinc atoms are four-coordinate with a distorted tetrahedral geometry. 

Many dithiocarbamate complexes of zinc, silver, cadmium or mercury improve emulsion stability, including bis(dibenzyldithiocarbamato)-zinc(II) or -cadmium(II) and silver(I) diethyldi-thiocarbamate. Cadmium salts, mixed with citric acid or tartaric acid and added to the emulsion, are reported to be effective. Mercury(II) complexes of ethylenediaminetetraacetic acid (EDTA) and related ligands and of solubilized thiols such as (4) can be used. Other coordination compounds reported include EDTA and related ligand complexes of Co and Mn, mixtures of Co salts with penicillamine (5) and macrocyclic complexes of Ag such as (6). The latter compounds may be used in diffusion transfer systems in which transferred maximum densities are stabilized. 

Thiocarbamates, upon treatment with 5-BuLi followed by addition of various electrophiles, lead to the formation of -substituted products in excellent yields and with high stereoselectivities with inversion of configuration, e.g., eq 48. Reductive cleavage with lithium aluminum hydride and zinc chloride occurs without loss of enantiomeric purity and provides good yields of the corresponding thiols. 4... 

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