Oxidation of secondary alcohols by conventional and microwave-assisted methods using molybdenum complexes of ONO donor ligands

New dioxidomolybdenum(VI) complexes, [(MoO2)-O-VI{Hdfmp(bhz)(2)}(MeOH)] 1, [(MoO2)-O-VI{Hdfmp(inh)(2)}(MeOH)] 2 and [(MoO2)-O-VI{Hdfmp(nah)(2)}(MeOH)] 3 of ligand H(3)dfmp(L)(2) I, are obtained by the condensation of 2,6-diformyl- 4-methylphenol (dfmp) and hydrazides (L) [L = benzoylhydrazide (bhz), isonicotinoylhydrazide (inh), and nicotinoylhydrazide (nah)], respectively. All these complexes are characterized in the solid state and in solution namely by elemental analyses, spectroscopic techniques (IR, electronic, H-1 and C-13 NMR) and thermogravimetric analyses. Single crystal X-ray analysis of complexes 1 and 3 confirms the coordination of the ligand in the dianionic (ONO2-) enolate-tautomeric form and one of the hydrazido moieties remains non-coordinated. Oxidation of secondary alcohols: 1-phenyl ethanol, 2-propanol and 2-butanol, catalyzed by these molybdenum complexes, using conventional liquid phase and microwave-assisted methods in the presence of 30% H2O2 as an oxidant has been tested. The effects of various factors, such as temperature and amounts of catalyst, H2O2 and solvent have been investigated. These alcohols under the optimized reaction conditions gave high yields of the respective ketone. Addition of an N-based additive reduces the reaction time considerably. Amongst the two methods studied, the microwave technique proves to be a time efficient system.