Preparation of pyridinemonocarboxylic acids by catalytic vapour phase oxidation of alkylpyridines. I. Oxidation of 2‐ and 3‐picoline and decarboxylation of 2‐ and 3‐pyridinecarboxylic acid in the vapour phase

Abstract

AbstractThe vapour phase oxidation of 2‐picoline with air using a singly promoted vanadium catalyst (V2O5/SnO2, mole ratio 1/1.5), at a temperature of 375°C and a space velocity of 6130 h−1, gave a 69% conversion with a selectivity of 64% for 2‐pyridinealdehyde. No pyridoin formation was detected. In the vapour phase oxidation of 3‐picoline using a doubly promoted vanadium catalyst (V2O5‐TiO2‐Na2O with V/Ti/Na=100/20/1.15) at a temperature of 400°C and a space velocity of 1450 h−1, a 94% conversion of 3‐picoline was obtained with a selectivity of 51% for niacin (3‐pyridinecarboxylic acid) and 1% for 3‐pyridinealdehyde. By varying the atom ratio V/Ti, the catalyst V/Ti = 100/25 was found to be the most active one. The decarboxylation of 2‐ and 3‐pyridinecarboxylic acid in the vapour phase was also investigated under the conditions used in the oxidation of the picolines to the acids. At 350°C about 90% decarboxylation of picolinic acid occurs under these conditions, while only a few per cent of the niacin decarboxylated to pyridine between 300 and 500°C.