The Mechanism of the Oxygen Effect on Hydrogen Bromide Reacting with Ethenoid Compounds

Abstract

Abstract When hydrogen bromide acts on the ethenoid linkage in the presence of oxygen, the first change to be characterized is the formation of a bromo radical from the unsaturated molecule and the bromine atom formed from hydrogen bromide and oxygen. In the formation of the bromo radical, if the double bond is situated at the end of a chain, the bromine atom takes preferably the terminal position, and, if an asymmetric carbon atom is produced by the addition of the bromine atom, inversion is accompanied. In the second stage of the reaction the radical, according as its nature and the conditions, either takes up hydrogen atom from hydrogen bromide to form a completed addition product and another bromine atom or splits off the bromine atom to regenerate the double bond. In either case the cycle of the changes is propagated by a chain mechanism. The action of oxygen, therefore, resembles that of light quantum in a photochemical reaction proceeding with a great quantum yield. The theory advanced in this paper is based on the experiments on the action of hydrogen bromide and oxygen on certain ethenoid compounds. The effect of reduced nickel will be discussed in a separate paper on the basis of a quite similar mechanism.