Volker A. Brehme

Bimetallic-Catalyzed Reduction of Carboxylic Acids and Lactones to Alcohols and Diols

The homogeneously catalyzed reduction of carboxylic acids with hydrogen was studied. Bimetallic catalysts consisting of a group 8 or 9 late transition-metal and a second group 6 or 7 transition-metal carbonyl showed a synergistic effect allowing the conversion in good yields under moderate conditions. Besides the effect of different catalyst precursors, the influence of temperature, hydrogen pressure, and catalyst concentration was investigated. An equimolar mixture of [Rh(acac)(CO)2] and [Mo(CO)6] showed the highest activity and was therefore applied to the reduction of lactones to diols. The reduction potential of the catalyst was found to be dependent on the ring size of the lactone used. Five-membered ring lactones were hardly converted to diols whereas six- and seven- membered ring lactones reacted easily.

Aqueous biphasic catalysis as a powerful tool for catalyst recycling in telomerization and hydrogenation chemistry

The synthesis of valuable ethers, carboxylic acids and alcohols has been achieved by telomerization and hydrogenation procedures using only butadiene, carbon dioxide, ethylene glycol and hydrogen as starting materials. High product selectivities and yields have been realized in all reaction steps and catalyst recycling has been achieved by liquid–liquid-two-phase techniques. This way, ecologically and economically favorable chemical syntheses have been demonstrated using the waste gas carbon dioxide and other cheap feedstocks.

Homogeneous and heterogeneous catalyzed three-step synthesis of 2-ethylheptanoic acid from carbon dioxide, butadiene and hydrogen

This paper describes the synthesis of 2-ethylheptanoic acid (2) by hydrogenation of the -lactone (1), which is on his part very well available by the reaction of butadiene with carbon dioxide. A two-step hydrogenation process was found to be the most successful reaction pathway. First of all the cleavage of the -lactone ring is applied. This process involves a homogeneously catalyzed two-phase hydrogenation with a water-soluble in situ rhodium-phosphine catalyst. The effects of ligand, temperature, hydrogen pressure and catalyst concentration have been examined. The catalyst containing aqueous phase has been recycled five times without loss of activity. The leaching of the rhodium into the organic phase was measured and found to be in the range of 1 wt.% of the starting catalyst concentration. The hydrogenation of the remaining double bonds was carried out with a heterogeneous palladium/charcoal catalyst in methanol.