Quantitative study of the oxidative discoloration of ethyl linoleate. I. Oxidation in the bulk phase

Abstract

The atmospheric oxidation of ethyl linoleate has been studied in the bulk phase at 22 and 50°. The concentrations of conjugated dienes, conjugated trienes (diene ketone), and the development of a yellow coloration were obtained as functions of time from extinction coefficients measured at 234, 268/275 and 350 mμ respectively. The energy of activation of the initial hydroperoxidation reaction agrees well with previously published data. The kinetics of hydroperoxide decomposition have been studied. There appears to be a direct relationship between the rate of hydroperoxide decomposition and the rate of yellowing. The conjugated diene ketone which is formed by a second‐order hydro‐peroxide decomposition is itself oxidised, but no simple relationship can be found between the rate of oxidation and the rate of yellowing. It is therefore concluded that the diene ketone is not a colourless precursor of the yellow compounds.

Insights into the yellowing of drying oils using fluorescence spectroscopy

“…This discoloration is an unavoidable property of oil paint [2]. The basis of the yellow colour remains poorly understood, despite the wide range of reported chemical compounds that are suspected to play a role in this regard [2,4,[26][27][28][29][30][31][32]. The currently accepted view is that the yellowing is a result of two compounds, one which reflects yellow light, and another which fluoresces yellow, however, their identities are still unknown.…”