Toshiharu Yokoyama

Hydrogenation of carboxylic acids to the corresponding aldehydes

In this article, the key issue of the catalysts for hydrogenation of aromatic and aliphatic carboxylic acids to the corresponding aldehydes was reviewed. For the hydrogenation of aromatic carboxylic acids, metal oxides, such as ZrO2, CeO2, ZnO and MnO, show high activity and selectivity to aldehydes. On the other hand, for aliphatic carboxylic acids which have two -hydrogen atoms, these metal oxides show low selectivity for hydrogenation, because undesirable ketonization occurs. For the hydrogenation of aliphatic carboxylic acids, Cr 2O3 and the partially reduced Fe2O3 show high selectivity. Especially, the highly pure Cr2O3 exhibits superior chemo-selectivity to aldehyde without C=C bond migration or ketonization. The chromium-modified ZrO2 catalyst for manufacturing aromatic aldehydes and the highly pure Cr2O3 catalyst for manufacturing aliphatic aldehydes have been commercially used in industrial processes. A new aspect of direct hydrogenation catalysts is briefly reviewed, and the reaction mechanism for hydrogenation of carboxylic acids is also discussed.

Formation of dihydrogen and carboxylic acid from water and aldehyde over metal oxide catalysts

Abstract The formation of dihydrogen and benzoic acid was observed from water vapor and benzaldehyde over Cr3+-promoted ZrO2,ZrO2 and Cr2O3 catalysts. Cr3+-promoted ZrO2 was the most active catalyst for this reaction and an equimolecular amount of dihydrogen and benzoic acid was obtained. Dihydrogen and the corresponding carboxylic acids were also obtained from the reaction of 3-phenoxybenzaldehyde or 1-heptanal with water. It is suggested that a surface carboxylate species formed by aldehyde adsorption is an intermediate of these reactions.

Direct hydrogenation of aliphatic carboxylic acids to corresponding aldehydes with cr2o3 catalyst

Abstract A new process for the production of aliphatic aldehydes was developed and commercialized. Using highly pure Cr 2 O 3 catalysts, we succeeded in hydrogenating aliphatic carboxylic acids directly to corresponding aldehydes in excellent yields. Noteworthy was that acids with a CdC double bond (e.g. 10-undecenoic acid [10-UDEA]) were selectively hydrogenated at the CdO group without hydrogenation or migration of their CdC bond to give 10-undecenal [10-UDEH]. Examination of the surface of Cr 2 O 3 indicated its neutral property, which was believed to be the reason for the high selectivity of this catalyst.