Trichloroethyl acetate

Other methods are based on bromochloroethane [25620-54-6] trichloroethyl acetate [625-24-1tetrachloroethane [79-34-5] and catalytic cracking of trichloroethane (5). Catalytic processes produce as by-product HCl, rather than less valuable salts, but yields of vinyUdene chloride have been too low for commercial use of these processes. However, good results have been reported with metal-salt catalysts (6—8). 

Bis(2,2,2-trichloroethyl) Acetals and Ketals R2C(OCH2CCl3)2 (Chart 5) Formation ... 

Other methods are based on bromochloroethane, trichloroethyl acetate, tetrachloroethane, and catalytic cracking of trichloroethane. Catalytic processes produce hydrogen chloride as a by-product. 

The homochiral prostaglandin precursor (15,3fi)-330.1 was prepared [Scheme 4.330] by selective hydrolysis of the /weso-diacetate of cw-4-cyclopentene-13-diol 330 2 using pig liver esterase (PLE),617 whereas the enantiomer (1/ ,35)-330 3 was the product of electric eel cholinesterase (EECE) hydrolysis,618 Since enzyme-catalysed reactions are reversible, transesterification can also be used to prepare esters. In the case at hand, ciy-4-cydopentene-l,3-diol (330.4) was enan-tioselectively transesterified using pig pancreatic lipase (PPL) and trichloroethyl acetate.619 The trichloroethyl ester is used in order to influence the position of equilibrium since trichloroethanol is a better leaving group and weaker nucleophile than cyclopentenediol.620... 

Protection of aldehydes and ketones. Treatment of a dimethyl or diethyl acetal with 1.5 eq. of trichloroethanoi in refluxing benzene under acid cataly.sis (p-TsOH) gives the mixed acetal use of 4 eq. of the alcohol gives the di-2,2,2-trichloroethyl acetal. 

However, several precedents in the literature would seem to negate a favourable outcome for such a scheme. For example, the treatment of 2,2,2-trichloroethyl acetate with zinc leads to 1,1-dichloroethylene in a dramatically exothermic process. Since chloroformate anion is a better leaving group than acetate, it should compete with chloride for that role. Chloroformate ion also should be lost in an anticipated subsequent zinc-mediated elimination to yield the explosive chloroacetylene. Moreover, the well-known decomposition of chloroformate in presence of zinc salts provides another problem. 

Table 11.1-25 list examples in which certain additives have an unambiguous beneficial influence on selectivity and/or reaction rate. The enantiomerically enriched or pure compounds 1-9 have been prepared under the influence of mainly triethylamine or other bases. In case of 1 for the acetylation with 2,2,2-trichloroethyl acetate there was no reaction without triethylamine. For the formation of 5 the reaction time was shortened dramatically from ten days to three hours for 100% of conversion. In most cases there is no rationale for the effects of bases except the formation of ion-pairs between the added bases and traces of acids present in the reaction mixture. Only for the synthesis of 9 a systematic investigations demonstrates that triethylamine besides its racemizing properties (cf. Table 11.1-24) has a significant influence on the water activity of the reacting mixture[138]. In other cases, triethylamine has been used as an additive without comparing its influence with the results in its absence1 331. 

A soln. of the startg. m. and Zn-dust in methanol refluxed 12 hrs. under argon -> dodecanal. Y 89%. - Advantages of the above protective group are efficient introduction and removal, stability toward many reagents, and selective removability. F. e. s. E. J. Corey and R. A. Ruden, J. Org. Chem. 38, 834 (1973) protection of carbonyl groups as mono- or di-2,2,2-trichloroethyl acetals cf. J. L. Isidor and R. M. Carlson, J. Org. Chem. 38, 554 (1973). 

Further examples of selective acylations and deacylations by means of enzymes, especially lipases, have been reported. Acetylation at the primary centre of H acetylneuraminic acid was performed by acyl transfer from 2,2,2-trichloroethyl acetate under catalysis porcine pancreatic lipase in pyridine, and use of an immobilised microbial lipase in a solvent-free process allowed selective 6-0-esterification of ethyl a-D-glucopyranoside with long-chain fatty adds. Under the same conditions methyl a-D-glucopyranoside and D-glucose reacted similarly but at much slower rates. ... 

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