On heating with the formate, triethylammonium formate, known as the distillable liquid given by 5HCO2H·2NEt3, several triphenylmethanes possessing dimethylamino group on their benzene rings have been shown to suffer reductive cleavage at the carbon bond bound to the dimethylaminophenyl carbon to give N, N-dimethylaniline and diphenylmethanes. The reaction is controlled by the structure and the substituent effect. Isotopic experiments using a deuterated formate has revealed that formyl hydrogen of formic acid is transferred to the methylene carbon of the diphenylmethane product. From the assembled data, a possible mechanism is proposed.