A method of preparing a compound of formula I ##STR00001## wherein R is a hydrocarbon and n is an integer from 1 to 5, including the steps of: contacting a compound of formula II ##STR00002## with a compound selected from the group consisting of amines, and carbonates, bicarbonates, and hydroxides of alkali metals, and combinations thereof, in a solvent to produce a salt of a compound of formula II; treating the salt of the compound of formula II in a polar, aprotic solvent with an organic halide having a formula R--X, wherein X is selected from chlorine, bromine, iodine, and combinations thereof, to produce an ester of formula I; isolating a reaction product including the ester of formula I from the solvent by precipitation or solvent extraction; and purifying the compound of formula I, is disclosed.