The Addition of Hydrogen Bromide to Cinnamic Acid and the Oxygen Effect

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Abstract
The action of the mixture of hydrogen bromide and oxygen on cinnamic acid in carbon tetrachloride produces ω-bromoacetophenone together with α,β-dibromohydrocinnamic acid. It is concluded that the free radical C6H5\.{C}HCHBrCOOH is formed in the intermediate stage in accord with the expectation from theoretical considerations concerning the stability of radicals. The radical, owing to its stability, does not react with hydrogen bromide to give α-bromohydrocinnamic acid, but reacts, on one hand, with oxygen ultimately to give ω-bromoacetophenone after disrupture of carbon dioxide and, on the other hand, with bromine or hydrogen bromide, as detailed in the text, to give α, β-dibromohydrocinnamic acid.