Polyethylene Glycols as Efficient Catalysts for the Oxidation of Xanthine Alkaloids by Ceric Ammonium Nitrate in Acetonitrile: A Kinetic and Mechanistic Approach

Abstract

Kinetics of oxidation of xanthine alkaloids, such as Xanthine (XAN), hypoxanthine (HXAN), caffeine (CAF), theophylline (TPL), and theobromine (TBR), have been studied with ceric ammonium nitrate (CAN) using poly ethylene glycols (PEG) as catalysts. Reaction obeyed first order kinetics in both [CAN] and [Xanthine alkaloid]. Highly sluggish CAN-xanthine alkaloid reactions (in acetonitrile media even at elevated temperatures) are enhanced in presence PEGs (PEG-200, -300, -400, -600). An increase in [PEG] increased the rate of oxidation linearly. This observation coupled with a change in absorption of CAN in presence of PEG, [H–(OCH2–CH2)n–O–NH4Ce(NO3)4(CH3CN)] (PEG bound CAN species), is considered to be more reactive than CAN. The mechanism of oxidation in PEG media has been explained by Menger-Portnoy’s enzymatic model.