Preparation of Crystalline CrVO4 Catalyst by Soft Chemistry Technique and Application for Vapor-phase Oxidation of Picolines

Partial oxidation of 2-, 3and 4-picolines has received much attention because their oxidation products, picolinic acid, nicotinic acid and isonicotinic acid, respectively, are valuable intermediates of vitamins, food additives and pharmaceuticals1)~16). For example, 2-pyridinecarbaldehyde and picolinic acid are vitamins, feed stocks for synthesis of physiologically active substances, dyes and other synthetic chemicals. Nicotinic acid is an important vitamin of the B-complex and so is its amide. Many drugs17) based on nicotinic acid have curative effects such as: lowering the level of cholesterol and free fatty acids in the blood, stimulation of the respiratory apparatus, antispasmodic and antirheumatic action etc. The isonicotinic acid has been used in the form of its hydrazide, in the treatment of tuberculosis. Now, 2-, 3-, and 4-pyridinecarbaldehydes and 2-, 3-, and 4-pyridinecarboxylic acids are usually prepared by oxidizing the corresponding alkylpyridines in the liquid phase. However the use of stoichiometric oxidants known to be toxic and expensive complexes and also the use of environmentally unfriendly organic solvents have been identified to be the major limitations of this method. These limitations of conventional way of picoline oxidation necessitated the development of catalytic methods using clean and atom-efficient oxidants like molecular oxygen without organic solvents. Solid, heterogeneous catalysts have the advantages of ease of recovery and recycling, and are readily amenable to continuous processing. Therefore, the vapor phase oxidation of organic compounds over heterogeneous catalysts with molecular oxygen is environmentally acceptable from the viewpoint of “green chemistry,” and its wide applications are being found in chemical industry by replacing some harmful liquid oxidation processes. The vapor phase oxidation of 3-picoline has been performed on a series of vanadium containing catalysts such as V2O5/TiO28),11)~14),19), V2O5/SnO2, and over225 Journal of the Japan Petroleum Institute, 54, (4), 225-236 (2011)