Terpene hydroperoxide chemistry in citrus oils; reaction with endogenous aldehydes to form peroxyhemiacetals

Abstract

AbstractLimonene and linalool are major components in many essential oils, and both readily autoxidize to form terpene hydroperoxides. These hydroperoxides are sensitizers capable of causing allergic contact dermatitis, so it is important to have accurate analytical methods for them in perfumery raw materials and formulations. This laboratory has previously reported a method to detect terpene hydroperoxides based on high‐performance liquid chromatography using a post‐column chemiluminescence reaction. Using this method, it was shown that peroxyhemiacetals formed by reaction of terpene hydroperoxides with endogenous aldehydes exist as components in common citrus oils. This was further substantiated by NMR analysis using a variety of techniques. Some percentage of the peroxyhemiacetals can dissociate back to the corresponding parent terpene hydroperoxides and aldehydes under certain conditions which are currently not fully understood, even if the polarity of the solvating environment appear to be important. However, gas chromatographic analysis indicates that there may also be alternative degradation pathways. The presence and chemical behaviour of peroxyhemiacetals must be studied further and analytically accounted for, if meaningful results are to be obtained in the context of the dermal sensitizing potency of a sample. Copyright © 2016 John Wiley & Sons, Ltd.