Synthesis and kinetic analysis of green AA-type monomers using linoleic acid through bromide promoted transition metal-catalyzed oxidation with air

Abstract

The present study explores the renewable route to synthesize AA-type monomers for condensation polymerization, namely adipic and azelaic acid, from linoleic acid (LA) using a bromide-promoted transition metal catalyst. For this, liquid-phase catalytic oxidation of LA is carried out using a catalyst system involving the acetates of Cobalt(II) and Manganese(II) and hydrogen bromide in an acetic acid green solvent at temperature: 393–423 K and a pressure of 5.8–8.8 bar in the air. The oxidation products are confirmed by a gas chromatography-mass spectrometer and carbon dioxide analyzer. At the early stage of LA oxidation (i.e.,<5.0 h), the identified major products are malonic acid, azelaic acid, and adipic acid, whereas malonic acid decomposes to carbon dioxide after increasing oxidation time. The influence of process variables, i.e., (i) the loading of LA, bromide, Cobalt(II), and Manganese(II), (ii) temperature, and (iii) pressure on LA conversion and yield of adipic acid and azelaic acid have also been carried out, and the loading of catalyst, pressure, and temperature plays a vital role on the LA conversion and product yields. The temperature-dependent kinetic parameters are also determined, and the rate-controlling step for LA oxidation is analyzed and further extended by evaluating the Hatta number and enhancement factor. The lower values of the Hatta numbers and enhancement factors suggest that the oxidation using air is controlled by the diffusion of oxygen and reaction in the film, and adequate gas-liquid mixing will improve the rate of LA oxidation.