Organic-water interfacial synthesis of α-tetralone using nickel-tetraethylenepentamine complex catalysts

Biphasic autoxidation of tetralin to alpha-tetralone has been carried out using surface-active ligand complexes of nickel as catalysts, tetralin as the substrate and organic phase, and dodecyl sodium sulfate as an emulsifier. The major products formed under the mild reaction conditions of 60 degrees C acid 1 atm were alpha-tetralone and alpha-tetralol, and the highest selectivity of 71% to the preferred product alpha-tetralone was obtained with nickel-tetraethylenepentamine complex, Depending on the ligand used, ligand to catalyst ratio of 2:1 or 1:1 was optimum accelerating the reaction rate and phase separation. The organic-water phase volume ratio around which the maximum reaction rate was obtained varied somewhat with the ligand used in the reaction, but generally 1 : 1 or 2:1 was adequate, The reaction order with respect to oxygen shifted from first to zero as its partial pressure increased and the reaction order with respect to nickel catalyst concentration varied from 1.7 to 1, and subsequently to 0 with further increases in the metal concentration. A kinetic model based on a free radical mechanism is proposed which yields a rate law in accord with the experimental findings. (C) 1998 Academic Press.