Abstract: In a process for purifying carboxylic acids comprising halogen compounds, the carboxylic acid is distilled in the presence of a nonvolatile auxiliary base, the halide of which is liquid at the boiling temperature of the carboxylic acid. The auxiliary base binds the hydrogen halide which is present in the carboxylic acid and/or has been eliminated from halogen compounds as a result of thermal action and lowers the vapor pressure thereof in this way, such that the hydrogen halide is held in the distillation bottoms and is not transferred into the distillate. Since the halide of the auxiliary base is liquid, the formation of solid deposits in the distillation apparatus is prevented. The carboxylic acid optionally also comprises at least one low boiler.