Decarboxylation, transition metal-catalysed

The decarboxylation of free carboxylic acids is often difficult except for some activated acids such as aryl carboxylic acid. Conversion of the free carboxylic acids into proper derivatives snch as acid anhydrides or esters makes the transition metal-catalysed decarboxylation reaction easy and these have also been applied to various coupling reactions. Water in a snpercritical stage (374°C, 22 MPa) was used for decarboxylation of free carboxylic acids using 10 wt% Pd on active carbon in a closed pot (Matsnbara et al., 2004) (Scheme 3.14). 

The formation of MAHs in soft drinks and some foods can be explained by decarboxylation of aromatic acids, whether natural or used as additives. The second case corresponds to the formation of benzene in soft drinks and fermented vegetables preserved with benzoic acid, which in the presence of ascorbic acid can yield benzene by decarboxylation. The reaction is catalysed by traces of transition metals. Traces of benzene found in cranberry and mango products that were not preserved with benzoic acid were due to a higher content of naturally present benzoic acid. 

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