THE INDIRECT ANODIC-OXIDATION OF 2-METHYLNAPHTHALENE .1. RUTHENIUM COMPOUNDS AS CATALYSTS

The indirect anodic oxidation of 2-methylnaphthalene and naphthalene to 2-methylnaphthoquinone-1, 4 and naphthoquinone, respectively, was carried out with RuCl3.3H2O, Ru(acac)3 and Ru(NH4)2Cl6 as catalysts, in an undivided cell using platinum electrodes. Current-potential analysis of the hydrocarbon shows two oxidation waves in solutions of acetonitrile-H2SO4 which collapse into a single wave in presence of water, implying an electrodic-chemical-electrodic (ECE) reaction sequence. RuCl3.3H2O or Ru(NH4)2Cl6 increases the selectivity for quinone formation, whereas Ru(acac)3 has no such effect. Voltammetry shows that RuCl3.3H20 and Ru(acac)3 oxidize water and not the hydrocarbon. It also identifies an activated complex in which RuCl3.3H20, but not Ru(acac)3, binds to the oxidised form of the hydrocarbon. This analysis explains the catalytic effect of RuCl3.3H20 and the inefficiency of the coordinatively saturated Ru(acaC)3. RuCl3.3H2O is also an efficient catalyst in non-acidic solutions containing high concentrations of diisobutylamine and diisopropylamine and in which oxidation of 2-methylnaphthalene to 2-methylnaphthoquinone-1,4 is possible at a very low potential.