Electronic, steric, and temperature effects in the Pd(II)-biquinoline catalyzed aerobic oxidation of benzylic alcohols in water

The Pd-catalyzed aerobic oxidation of various benzyl alcohol derivatives was investigated. Product selectivity is highly dependent on the nature and position of the substituents on the alcohol as well as the level of catalyst loading. Electron-donating substituents increase the reaction rate (p = -0.37), which suggests a partial reduction of the palladium center coupled with alcohol oxidation in the rate-limiting step. The temperature dependence of 4-methoxybenzyl alcohol oxidation was also evaluated, providing activation parameters of Delta H-double dagger = 7.4(4) kcal/mol and Delta S-double dagger = -53(1) cu. Water is used as the only reaction solvent and air is used as the sole oxidant throughout these studies. (C) 2008 Elsevier B.V. All rights reserved.