Liquid-phase Autoxidation of Hexanal

Abstract

In order to obtain fundamental data on the oxidation of saturated aliphatic aldehydes in the liquid-phase, the effect of solvents was studied. The oxidation reactions were performed at 0°C, 30°C and 40°C under atmospheric pressure of oxygen in varuous solvents in the presence or absence of radical initiator and cobalt catalyst. The rates of oxidation differed by a factor of 2.7 with the structure of aldehydes and the rates in ethyl acetate were always a little higher than those in chlorobenzene. Regardless of the kind of solvents or presence of catalyst, the initial rate of oxygen absorption was first order with respect to hexanal concentration. Except for some solvents, the rates of oxidation was correlated with (D-1) /(2D+1), where D is the dielectric constant of the solvent. The ester solvents, especially ethyl acetate, gave faster rates and higher yields of peroxy acids than non-ester solvents. The oxidation did not proceed in methanol even in the presence of metal catalyst. The rate of oxidation increased with the yield of peroxy acid. This indicates that the decomposition of peroxy acid affected the rate of the oxidation.