Reactivity of fluorine in fluorinated succinic esters

Abstract

In basic medium, dimethyl and diethyl erythro- and threo-α-bromo-α′- fluorosuccinate eliminate hydrogen fluoride considerably faster than hydrogen bromide. The reaction rate depends slightly on the concentration of the ester, and strongly on the concentration of the base (acetate). Methyl esters react considerably faster than ethyl esters, threo isomers slightly faster than the erythro isomers. The negligible difference in the rates of elimination of hydrogen fluoride from the two diastereomeric esters constrasts sharply with the large difference in the rates of elimination of hydrogen bromide from the two corresponding dibromo esters, meso- and DL-α,α′-dibromosuccinates. The elimination of hydrogen fluoride from the bromofluoro esters is evidently influenced not only by steric factors but also by attraction between hydrogen and fluorine (possibly hydrogen bonding) which can account for the considerable proportion of cis elimination in the case of the erythro isomer.