Hydrocarboxyl radicals

Scheme 2.8 Main radical mechanism of the hydrocarboxylation of alkanes with peroxydisulfate, CO, and water, in aqueous (H20/MeCN) medium [51]. The minor 7 (or 7a) to 8 alternative pathway does not concern water as the hydroxylating agent. (5ee insert for color...

The initial steps of the mechanism of the alkane (RH) carboxylation (Scheme 2.9b) [52, 53] are identical to those of the hydrocarboxylation, discussed above, with S20g as the source of the sulfate radical, which acts as H-abstractor from the alkane to give the alkyl radical R, and CO as the carbonylating agent of this radical to yield the acyl radical RC 0. 

A simplified mechanistic pathway (Scheme 3.11) was proposed [14, 15, 18] for the Cu-catalyzed hydrocarboxylation of various alkanes (RH) on the basis of experimental data, including the analysis of various selectivity parameters [14, 18-21], tests with radical traps [18-20] and 0-labeled H2O [18], DPT calculations, and other studies [18, 33]. It includes the following steps [12-15, 18-22] (1) generation of the alkyl radicals R from an alkane [formed via H-abstraction by... 

It is important to note that the hydrocarboxylation and carbonylation catalytic cycles involve common intermediates, but there are clear differences. In the hydrocarboxylation reaction, there is no oxidative addition or reductive elimination step, and all the intermediates have Rh. Other Fe-, Ru-, Co-, Rh-, Ir-, Pd-, and Pt-based hydrocarboxylation and/or hydroesterification catalysts are also known. Eastman Chemical has reported a Mo(CO)g-catalyzed ethylene hydrocarboxylation process that involves a radical mechanism. 

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