Abstract: A process of purifying a (6-chloro-2-carbazolyl)methyl-malonic acid di(C.sub.1 -C.sub.6 alkyl) ester of Formula (I): ##STR1## wherein R.sub.a and R.sub.b must be the same and are selected from the group consisting of C.sub.1 -C.sub.6 alkyl; comprises phase separating one or more impurities from said carbazole ester at least once wherein the solvent used to carry out said phase separation is acetic acid. In a preferred embodiment said acetic acid is glacial acetic acid which is maintained at a temperature of from about 30.degree. to about 110.degree.0 C. and said carbazole ester is obtained in a purity of at least 99.90% by weight, so that the amount of impurities present therein is 0.10% or less by weight. In a more preferred embodiment of said process, said temperature is from about 50.degree. to about 70.degree. C., and said phase separation is carried out only once.