Iodine Value of Rubber and Gutta-Percha Hydrocarbons As Determined by Iodine Chloride

Abstract

Abstract HALOGEN absorption methods employing solutions of bromine, iodine bromide, or iodine chloride are widely used for determining the unsaturation of organic compounds. In the use of these methods the choice of halogen reagent, the amount employed, and the time and temperature for the reaction are all important factors which must be given careful consideration in order that the best results may be obtained. Certain structural differences in unsaturated organic compounds may have a decided influence on the reactivity of these substances toward halogens. For example, the presence of negative groups on one or both of the unsaturated carbon atoms protects against halogen addition; thus maleic or fumaric acids do not add iodine chloride (7). Styrene adds iodine chloride quantitatively, but in the case of cinnamic acid only a slight reaction takes place (4). No addition of iodine chloride occurs with dichloroethylene and very little with vinyl bromide (3). The authors have found that polyvinyl chloride (DuPrene) adds iodine chloride to only 30 per cent of theory. A triple-bonded compound, such as diphenylacetylene (4), shows only partial addition of iodine chloride, as would be expected from the negative effect of the first additive halogen. The unsaturated terpenes vary widely in their reactivity with halogens, extensive substitution occurring along with addition (5), particularly in the case of pinene. Aside from these complications, however, numerous investigators have shown that one or more of the halogens add quantitatively to a wide range of unsaturated hydrocarbons, acids, glycerides, alcohols, esters, etc. Of the many methods proposed the well-known Wijs procedure involving the use of 0.2 N iodine chloride in glacial acetic acid has been widely used and accepted.