Lithium chloride as a catalyst in the halogenation of organic compounds

Abstract

In recent years the various factors involved in the addition of halogens to unsaturated compounds has received considerable attention resulting in the elucidation of some apparently complex problems. The main theme of this investigation has been the study of lithium chloride catalysis on the addition of bromine and chlorine to unsaturated organic substances. At the same time some constitutional effects have been studied. In the bromination of aromatic compounds in acetic acid Robertson, de la Mare and Johnston (J.C.S., 1943, 276.) found that the reaction was generally complicated by the acid catalytic effect of the hydrobromic acid liberated. They also found that the rate of substitution, which has been shown to have many resemblances with olifinic addition, was affected by added sulphuric acid. Previously Robertson, Clare, McNaught and Paul (J.C.S., 1937, 335.) had pointed out that αβ-olefinic acids and certain vinyl compounds reacted differently on the addition of hydrobromic acid to the reaction mixture from the normal bromine addition, in that acrylic acid was strongly catalysed while cis-cinnamic and dimethyl acrylic acids showed only slight catalysis. Furthermore the acid catalysed reaction rate, unlike normal bromine addition, was reduced by adding water to the solvent.