RARE-EARTH TRIFLUOROMETHANESULFONATES AS CATALYSTS IN SOME MEERWEIN-PONNDORF-VERLEY TYPE REDUCTIONS

Rare earth cations catalyze the reduction of aldehydes and ketones by isopropanol. The reaction rate constants have been determined by H-1 NMR spectroscopy in the presence of La3+, Y3+, Lu3+, Sc3+, using Cl-, ClO4- and TfO- as counterions; the values obtained indicate that the reaction rates increase as the cation size decreases and with the use of poorly co-ordinating counterions. Scandium trifluoromethanesulphonate turned out to be by far the best catalyst for these reactions. By comparison of strictly analogous aldehydes and ketones it has been found that the former compounds are more easily reduced than the latter. The formation of mixed ethers with isopropanol was observed during the reduction of aromatic carbonyl compounds substituted with electron donating groups.