The effect of the cathode material on the electrochemical activation and dehalogenation of C-2 freons

Abstract

Such reactions lead to the formation of valuable chlorotrifluoro-or tetrachloroethylenes. It was found that a silver cathode has a promoting effect on the investigated processes compared with the other materials (GC, Pt). The optimum reaction conditions within the present investigation were determined.The processes involved in the electrochemical activation of Freons and their use in the synthesis of important organic products have attracted the attention of many research workers in recent years [1][2][3][4][5][6][7]. A promising feature of the electrochemical conversion of Freons is their use as sources of fluoroalkyl groups in the fluoroalkylation of various organic substrates [1].Another no less important development is the dehalogenation of Freons C-2, including the process involving the use of various electron transfer mediators [2-7] and leading to the formation of fluorine-containing ethylenes, which are valuable products for the synthesis of fluoroplastics, biologically active substances, and other products. At the same time, in spite of the appeal of such processes, many important aspects of their realization remain unclear or have been poorly developed. This concerns, primarily, the effect of the cathode material, the nature of the electrolyte, and other factors on such processes.In the present work we studied the electrochemical activation of Freons F113 (CF 2 ClCFCl 2 ), F113B2 (CF 2 BrCFClBr), and F114B2 (CF 2 BrCF 2 Br) at various electrodes, i.e., at platinum as a material widely used in electrochemical investigations, at glassy carbon as a material not exhibiting significant specific adsorption of halogen-containing compounds [8,9], and at silver for which such an effect can be clearly observed in certain halogen-containing compounds [9][10][11][12][13][14][15][16]. EXPERIMENTALThe Freons were dried with calcium chloride for 12 h and were then distilled at atmospheric pressure. Dimethylformamide (DMF), dehydrated with calcium chloride for 6 h and double distilled under vacuum with intermediate drying by 4A molecular sieves, was used as solvent. The indifferent electrolyte was LiBF 4 , which was dried under vacuum at 100°C for 24 h and further dried in a muffle furnace at 110°C just before the experiment. The electrochemical experiments were carried out with a computerized setup based on an EP 20A potentiostat in an undivided three-electrode cell with platinum, silver, or glassy carbon (GC) point working electrodes of 2 mm diameter and a platinum auxiliary electrode. The concentration of the Freons in the voltammetric experiments amounted to 0.02 M, and the concentration of the indifferent electrolyte was 224 0040-5760/06/4204-0224

Electrochemical activation and dehalogenation of freons in low-temperature ionic liquids

“…4). Similar relationships, which we observed earlier in the case of the reduction of Freons in DMFA [15], are also characteristic of other LTILs and Freons.…”

“…This can explain the less significant shifts of the potential and the increase of the peak current in the case of the bromine-containing Freons F114B2 and F113B2. The specific effect of silver on the electrochemical activation of the Freons in the LTIL is similar to that observed in DMFA [15] and agrees with the data in [20,22], in which in particular the effect of a silver cathode on the processes in the electrochemical activation of certain other halogen-containing compounds in traditional organic solvents was examined.…”

“…This is probably due to the different mechanism of the transformations in the cathodic activation processes of these Freons. Thus, in DMFA, as shown in [15], the reduction of F113 takes place through the removal of two halide anions and leads to chlorotrifluoroethylene. In contrast, the cathodic reduction of F13B1 can take place with the formation of the CF 3 ⋅ radical with its subsequent transformations, as observed in [16].…”

“…On the other hand, as shown in [15], the electrochemical activation processes of the Freons involve the elimination of a halide anion in the course of their cathodic reduction. In view of the fact that the 1-butyl-3-methylimidazolium (I), 1-butyl-1-methylpyrrolidinium (II), and 74 Fig.…”

Electrochemical activation of freons and their joint conversion with sulfur and carbon dioxides

“…Another important factor affecting the process of cathodic activation of the Freons is the material of the electrode. Thus on changing the glassy electrode to silver led to a considerable shift of the peak potential for reduction for both the vicinal and geminal Freons (DE » 0.5-0.8 V) to a less negative field which may be linked with the catalytic properties of Ag in the processes of cathodic activation of halogen-containing compounds [11][12][13][14][15], including the ability of silver atoms at the electrode surface to form complexes (AgLHalLR f ) with the Freon by which breaking of the C-Hal bond is facilitated.…”