2-Chloro-4,5-difluorobenzoic acid (CDFBA) and related impurities are determined using liquid chromatography (LC). Separations are achieved using a reversed-phase isocratic system with an ion-pair reagent (tetrabutylammonium hydroxide). Unique isomeric impurities observed in commercially produced CDFBA were isolated and identified by NMR and single crystal x-ray diffraction. The method has relative standard deviations of ± 0.55% to ±1.26% for the CDFBA determination and from ±4.3% to ±12% for impurities below 0.3% in CDFBA. Impurities are determinable to at least 0.03% by weight.

The effects of mixed solvent systems and anions on the rate of reaction of the title compounds were investigated. The results were shown to be best interpreted in terms of ion-pair formation and solvation-desolvation effects, in addition to the factors included in the outer-sphere electron transfer rate theory expounded by Marcus.