The thermal decarboxylation of acids over a metal oxide catalyst

3 THE THERMAL DECARBOXYLATION OF ACIDS OVER A METAL OXIDE CATALYST 

A long-established method of formation of symmetrical ketones (albeit in rather low yield) involves the pyrolysis of certain salts (usually calcium or barium) of carboxylic acids. 

The method has been extended to include the synthesis of aldehydes or of unsymmetrical ketones by using appropriate mixtures of carboxylate salts. 

The unsymmetrical carbonyl compound will clearly be accompanied by both possible symmetrical products, but the yield can be improved by the use of an excess of one of the carboxylate salts. 

A more satisfactory process for the preparation of either symmetrical or unsymmetrical ketones involves the passage of the vapour of the acid or mixture of acids over heated manganese(n) oxide or thorium oxide deposited upon pumice. The yields of unsymmetrical ketones are satisfactory (c. 50%) and the technique is particularly well suited for laboratory preparations on a reasonably large scale. Several examples are included in Expts 5.92 and 5.93. 

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The thermal decarboxylation of acids over a metal oxide catalyst (Expts 5.92 and 5.93). 

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