Identification of halogen adducts of olefins in iodine value determination by HPLC

Abstract

Addition reaction of iodine-halogen to olefinic compounds is used for the determination of iodine value, although the value obtained by Hanus method is lower than that by wijs method. In this study, unsaturated compounds such as oleic acid, linoleic acid and styrene were reacted with IBr, ICl and Br₂. For UV monitor, halogen adducts of fatty acids were derivatized with phenacyl bromide. Separation of halogen adducts was investigated with a reversed phase HPLC system. In styrene, halogen adducts were separated each other, but IBr addition resulted in the formation of two bromine adducts. The halogen adducts of long chain unsaturated fatty acids were fractionated by preparative HPLC, because their HPLC separation was difficult. Fractionated halogen adducts were converted to halide ion by the oxygen combustion flask method. Halogen species were identified by the retention time of anion exchange chromatography and their abundances were determined by peak area. In the case of IBr addition reaction, only bromine adduct was observed for both oleic acid and linoleic acid.