INFLUENCE OF RU PRECURSOR, SUPPORT AND SOLVENT IN THE HYDROGENATION OF CITRAL OVER RUTHENIUM CATALYSTS

A series of ruthenium supported catalysts were prepared and investigat ed in the liquid-phase hydrogenation of citral. The mechanism of the r eaction was found to be dependent on the Ru precursor, support and sol vent used. On the sample prepared from RuCl3 the acetals of citronella l were formed with the subsequent hydrogenation of the isolated C=C do uble bond. On the samples obtained from precursors which do not contai n chloride ions, citronellal was the main reaction product. Hydrogenat ion of the isolated C=C double bond was negligible. Using cyclohexane as solvent, a large amount of isopulegol was also obtained. The result s of the hydrogenation of citral have been correlated to the presence of acid sites and incompletely reduced ruthenium which favour cyclizat ion and acetals formation from citronellal. On the basis of the report ed results, a reaction scheme for hydrogenation of citral over rutheni um catalysts is proposed.