Reaction of hydrogen bromide with diols of long chain α,β-unsaturated acids

The reaction oferythro- andthreo-glycols oftrans-2-hexadecenoic andtrans-2-docosenoic acids with hydrogen bromide in the presence of acetic anhydride has been investigated. In each case,erythro-2,3-dihydroxy acid gave a separable mixture of isomericthreo-2(3)-bromo-3(2)-acetoxy acids. In contrast,threo-2,3-dihydroxy acid yielded only one isomericerythro-2-bromo-3-acetoxy acid. The structures of individual bromo-acetoxy acids have been established by chemical as well as spectral studies. Stereoselectivity observed in the reaction of hydrogen bromide withthreo-glycol has been explained on the basis of different conformations of the diastereoisomeric 2,3-glycols.