HYDROQUINONE OXIDATION CATALYZED BY PYRIDINE-CU(II) COMPLEXES ATTACHED TO POLYORGANOSILOXANE .2. ELUCIDATION OF FACTORS RELATED TO CATALYTIC ACTIVITY

The oxidation of hydroquinone catalyzed by pyridine-Cu(II) complexes a ttached to polyorganosiloxane was investigated in the mixed solvent of methanol/water (vol. ratio 2/1). The catalytic oxidation followed Mic haelis-Menten-like kinetics. The large hz term related to a turnover n umber indicated that the present polymeric catalysts have a remarkable effect on the activation process. The methylene number between the si de-chain acid amido and pyridyl groups of the polymeric ligand was sho wn to be closely related to the appearance of hydrophobic effects in b oth the substrate-binding and the activation processes as deduced from the Michaelis constant and the thermodynamic and activation parameter s. The binding parameters for 4-methoxyphenol with pyridyl-functionali zed polyorganosiloxanes supported that the flexible backbone is also e ffective in the oxidation of hydroquinone. The Cu(II) complexes with p yridyl-functionalized polyorganosiloxane would have the structures dis torted from square planar formation, which would promote the reduction of Cu(II) to Cu(I), as concluded from ESR spectroscopy and electroche mical measurement. (C) 1994 John Wiley & Sons, Inc.