THE FORMATION OF KETONES AND ALDEHYDES FROM CARBOXYLIC-ACIDS, STRUCTURE-ACTIVITY RELATIONSHIP FOR 2 COMPETITIVE REACTIONS

Four carboxylic acids with a number of alpha-hydrogen atoms ranging fr om three to zero were tested in the selective hydrogenation to aldehyd e. The acids used were acetic, propanoic, isobutyric, and pivalic acid . The oxides of iron, vanadium, zirconium, and titanium were used as c atalysts. It was found that by decreasing the number of alpha-hydrogen atoms the selectivity to the aldehyde increased, while the formation of the main by-product, ketone, was suppressed. It is suggested that t his is due to the fact that the ketonisation proceeds via a ketene-lik e intermediate, the formation of which needs the presence of alpha-hyd rogen. Furthermore, the reactions to aldehyde and ketone seem to be in competition with each other.