Reaction of Nitrogen Dioxide with Alkenes and Polyunsaturated Fatty Acids: Addition and Hydrogen Abstraction Mechanisms

Article abstract of DOI:10.1021/ja00388a035

The reactions of nitrogen dioxide in a carrier gas (nitrogen, oxygen, or air) with cyclohexene and a series of mono-, di-, and trienes is reported at NO2 concentrations ranging from 70 ppm to 50percent.A complete product analysis was made with cyclohexene, and these data allow the calculation of the fraction of the NO2 that reacts by addition to the double bond or by abstraction of an allylic hydrogen.At high concentrations of NO2, addition is the predominant process, in agreement with the literature.However, below 10 000 ppm (1percent), hydrogen abstraction predominates.We suggest this is because of competition between a reversible addition and an irreversible H-abstraction step, much as is the case for the well-known bromine atom reaction system.In fact, a kinetic analysis shows that the ratios of rate constants for addition and abstraction are similar for both NO2 and the bromine atom.A less direct method (analysis of water formed) was used to estimate the addition to abstraction ratio for other alkenes and for esters of unsaturated fatty acids; these data are in agreement with the cyclohexene data.The autoxidation of unsaturated fatty acid esters initiated by NO2 also was studied, and kinetic chain lengths and autoxidizability ratios are given.