Oxidation of FA with alkene of alkyne functionalities studied with chemiluminescence and real‐time IR spectroscopy

Abstract

AbstractThe oxidation of well‐defined FA derivatives has been studied with real‐time IR (RTIR) and chemiluminescence (CL) techniques. Both methyl esters and model oils based on different FA have been studied to reveal the effect of functionality. The FA used were linoleic and crepenynic acid, the latter with an alkyne functionality. The purpose was to reveal how structural differences affect the oxidation and how this is monitored with CL and RTIR. Both model oils had longer oxidation induction times than the corresponding methyl esters, as seen by both IR and CL. Generally, the induction times measured with IR were shorter than those determined by CL, but the rate of oxidation did not seem to differ much between the model oils and the corresponding methyl esters. The results also imply that the higher functionality of the model oils gives a greater possibility of intramolecular addition reactions instead of chain scission during oxidation, making the model oils emit fewer low‐M.W. volatiles than the methyl esters. There is also a difference between methyl crepenynate and methyl linoleate, in that the alkyne functionality seems to enhance the possibility of chain scission instead of addition reactions. The results presented imply that the CL signal can be used to monitor the oxidation and the formation of volatile compounds from a FA structure. By combining the CL measurements with RTIR data, information about the oxidation reactions can be obtained, giving a greater understanding of what reactions are occurring during oxidation and how they are related to each other.