Carbonyl compounds carbon-chlorine bond formation

An alternative method for the formation of aldehydes or ketones makes use of the complexes formed from a methyl sulfide with chlorine or A-chlorosuccinimide (NCS), in what is called the Corey-Kim oxidation. With dimethyl sulfide the salt 28 is generated and reacts with the alcohol to give the alkoxysulfonium salts and hence, on treatment with a base, the carbonyl compound. This reaction has fovmd particular application in the oxidation of 1,2-diols in which one alcohol is tertiary, to give a-hydroxy-aldehydes or ketones without rupture of the carbon-carbon bond. For example, the aldehyde 32 is formed in good yield from the diol 31 using dimethyl sulfide and NCS followed by addition of triethylamine (6.29). This transformation is thought to depend on the preferential five-membered transition... 

In summary, the initial formation of an allylic radical anion on the metal surface is the most likely event, which would explain the success of indium, as its first ionization potential is particularly low E - 5.79 eV). In tin- and indium-mediated reactions the second step should be the insertion of the metal cation into the carbon-bromine (chlorine) bond to afford organometallic intermediates, which are stable enough to be produced, but also highly reactive toward carbonyl compounds in aqueous media. 

By contrast, consider the above reaction with R = HC=C. Depending on which enthalpy of formation value is chosen for chloroacetylene, we find an endothermicity of ca. 7 kJ mol" or an exothermicity of ca. 35 kJ mol". Either value clearly documents that the stabilization of chloroacetylene is considerably less than that of carbonyl chloride despite the considerably shorter C-Cl bond in the former. Bond lengths and bond strengths seemingly do not correlate for the above chlorinated species. We hesitate to suggest that it is inherently aproblem for chlorinated species as opposed to a too indiscriminate comparison involving compounds with such disparately hybridized carbons. 

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