REACTIONS OF IODINE ATOMS WITH n-BUTENES: II. INTERCONVERSION OF BUTENE-1 AND BUTENE-2

Abstract

In the vapor phase reaction of iodine atoms with n-butenes at 65 °C appreciable double-bond migration takes place in addition to the readily occurring geometrical isomerization. No detectable quantities of iodine-containing hydrocarbons are observed. In contrast to this, appreciable amounts of 1,3-butadiene and the corresponding amounts of hydrogen iodide are formed although direct abstraction of a hydrogen atom from butene by an iodine atom is unlikely in view of the endothermicity of this reaction. Formation of 1,3-butadiene is counterbalanced by its hydrogenation back to the original butene and its isomers and a steady state concentration is reached in the course of the reaction. As a consequence of this balancing of dehydrogenation and hydrogenation steps there is an induction period in the formation of butene-2 in the reaction of iodine atoms with butene-1 and a large part of butene-2 is found to be derived from the butadiene initially produced. To explain the occurrence of the endothermic steps, it is assumed that the initial iodine atom – butene adduct (iodobutyl radical or π-complex) interacts with a second iodine atom. Reaction mechanism is tentatively discussed.