Zinc diethyl carbamate

Standard rubber industry accelerators (e.g., CBS, diphenyl guanidine, mercaptobenzothiazole disulfide (MBTS) and zinc diethyl carbamate these can be used with or without other rubber chemicals, such as peptisers)... 

Sulfite paper has a relatively short life span, since residual acid will continue to hydrolyze the cellulose and cause embrittlement. Further sources of acid include aluminum sulfate (which is added together with resin to suppress bleeding or feathering of ink into the paper) and S02 and NO from the atmosphere. Much of the world s library collections and archives will soon be lost as the paper crumbles. Various deacidification treatments (e.g., with ammonia, morpholine, cyclohexylamine carbamate, or diethyl-zinc) have been proposed and tried, but at best they can only halt the process of embrittlement and cannot reverse it.14 With the move to kraft pulping, alkaline peroxide bleaching, and increasing use of precipitated calcium carbonate as a filler, the high quality papers produced today are intrinsically acid free and should also resist subsequent acidification by S02-polluted air fairly well. 

The efficiently chelated (zinc chloride, boron trifluoride diethyl ether complex), rigid five-mem-bered-ring dienophiles la and lb have been used in the enantioselective syntheses of several natural products. Thus, the reaction of (S)-l with 1,3-butadiene (5), promoted by zinc chloride (1 equiv) produces the cycloadduct ( + )-6 (83% d.r. 99 1), later converted to a precursor of (S)-sarkomycin (7). Cycloaddition of (S)-la with l,4-diacetoxy-l,3-butadicnc (8), catalyzed by boron trifluoride-diethyl ether complex (0.5 equiv) gives (-)-9 (72%) as a single diastercomer, further converted into (-)-shikimic acid (10) in a six-step procedure. Similarly, addition of (/ )-lb to 1,3-butadiene carbamate 11 in the presence of boron trifluoride-diethyl ether complex (1 equiv) produces ( + )-12 (95% d.r. 99 1), which was converted into ( + )-pumiliotoxin. 

Butanolysis of Af-(2-hydroxyethyl) amides (112) to the corresponding butyl ester (113) was catalysed by zinc triflate Zn(OTf)2 in the presence of diethyl carbonate (DEC) (Scheme 36a). The initial step of the process was a Zn +-catalysed N,0-acy rearrangement of (112) to produce a 2-aminoethyl ester (114), which suffered transesterification with butanol to yield the butyl ester (115) the by-product, 2-aminoethanol, reacted with DEC to give the cyclic carbamate (116), which prevented a facile reverse reaction (Scheme 36b). This new methodology was shown to effect selective bond scission at the amine side of a serine residue in several dipeptides. For example, the methyl ester of the Cbz-protected dipeptide, Ala-Ser (117), was cleaved into the Cbz-protected alanine butyl ester (118) in 64% yield (Scheme 36c). ... 

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