Electrochemical reduction of halogen containing compounds at a mercury cathode: Ethyl perfluoropropionate, butyrate, caprylate and glutarate

It has been found that RFCOOEt compounds with RF=CF3(CF2)n (n=1, 2, 6 for I, II, III) as well as COOEt(CF2)3COOEt(IV) and COOH(CF2)3COOH(VI) are reduced at a Hg electrode when dissolved in DMf+0.1 M Et4NClO4. No reduction occurs in the case of COOEt(CH2)3COOEt. I and II are reduced in a single one-electron step; III shows a single two-electron wave and IV exhibits two reduction processes each with n=2. Half wave potentials (E1/2/V) are: −2.14 (I); −2.09 (II); −2.04 (III); −2.00, −2.41 (IV). Compound VI shows two one-electron waves with E1/2/V: −1.30, −2.05. 19F n.m.r. data on III and IV are also reported. Cleavage of a C−F bond occurs as a consequence of reduction in I, II, III, IV. The two waves of VI are “hydrogen” waves. The effect of RF length on RFCOOEt reduction is discussed; electron attack on the carbonylic function is suggested; a close parallelism exists between the stability of RF− carbanions and the activation energy for the first electron transfer to RFCOOEt, indicating that inductive effects of the same kind are operative in both cases. The two-step reduction of diethyl perfluoroglutarate (IV) is discussed in terms of electronic effects and conformational requirements.