Effect of N-based additive on the optimization of liquid phase oxidation of bicyclic, cyclic and aromatic alcohols catalyzed by dioxidomolybdenum(vi) and oxidoperoxidomolybdenum(vi) complexes

Abstract

Two dioxidomolybdenum(VI) complexes, [Mo^VIO₂(L¹)(MeOH)] (1) and [Mo^VIO₂(L²)(MeOH)] (2) and their corresponding oxidoperoxidomolybdenum(VI) complexes, [Mo^VIO(O₂)(L¹)(MeOH)] (3) and [Mo^VIO(O₂)(L²)(MeOH)] (4) with ONO tridentate ligands, 4-[3,5-bis(2-hydroxyphenyl)-1,2,4-triazol-1-yl]benzoic acid (H₂L¹, I) and 3,5-bis(2-hydroxyphenyl)-1-phenyl-1,2,4-triazole (H₂L², II) have been synthesized and characterized by elemental analysis, spectroscopic techniques (infrared, UV-Vis, ¹H and ¹³C NMR) and thermogravimetric analysis. Structures of 1a (DMSO coordinated) and 2 (methanol coordinated) confirmed by single crystal X-ray study reveal that the tridentate ligands bind to the metal center through two oxygen atoms and a ring nitrogen atom. These complexes have been tested as catalysts for the homogeneous oxidation of bicyclic (isoborneol and fenchyl alcohol), aromatic (benzyl alcohol and cumic alcohol) and cyclic (cyclohexanol) alcohols, using 30% H₂O₂ as an oxidant. Various parameters such as amounts of catalyst, oxidant, solvent and temperature of the reaction mixture have been taken into consideration for the maximum conversion of substrates. Effect of N-based additive (NEt₃) on the conversion of substrates as well as selectivity of the corresponding product(s) under the optimized reaction conditions has also been checked and obtained results suggest that addition of an additive reduces time to achieve equilibrium and increases conversion of alcohols.