Electrochemical Synthesis of Cyanoacetic Acid from Chloroacetonitrile and Carbon Dioxide

Abstract

The electrochemical carboxylation of chloroacetonitrile was investigated in dimethylformamide ͑DMF͒ and acetonitrile ͑MeCN͒ by cyclic voltammetry and controlled-potential electrolysis. Both direct electroreduction and mediated reduction of the halide in CO 2 -saturated solvents were used to achieve the electrocarboxylation process. Also the effects of cathode material and cell type ͑divided or undivided with dissolving anode͒ were examined. In DMF the electrolyses performed in the divided cell resulted in low to moderate yields of NCCH 2 CO 2 H ͑25-45%͒, independent of the electrode material and catalyst type. The process is remarkably more efficient in MeCN, in which acid yields of ca. 60% were obtained under similar conditions. Very good results were obtained in both solvents when an undivided cell with aluminum sacrificial anode was used. In this case, the acid yield increased to 73 and 93% in DMF and MeCN, respectively.Cyanoacetic acid and its derivatives such as alkyl cyanoacetates are employed as starting materials in many industrial processes. 1 The current method of production of this acid makes use of the reaction between chloroacetic acid and alkali metal cyanides. 1 Alternative methods of synthesis, involving less dangerous reagents, have been described in a number of patents. [2][3][4][5] In particular, carboxylation of acetonitrile with CO 2 has attracted some attention. Kawamata et al. 4 and Tyssee 5 described the preparation of cyanoacetic acid by carboxylation of acetonitrile. This method requires deprotonation of CH 3 CN to NCCH 2 Ϫ , which is then trapped by CO 2 . To generate NCCH 2 Ϫ , Kawamata et al. 4 used alkali phenolates in DMF whereas Tyssee 5 used an electrochemical method. More recently, attempts to carboxylate acetonitrile by employing 1,3-diphenylurea or diphenylcarbodiimide in the presence of alkalimetal carbonates and CO 2 have given unsuccessful results. 6,7 Anodic oxidation of cyanoethanol 8 or some ␤-cyanoethyl ethers 9 at a Pt or PbO 2 electrode in 1.6 M H 2 SO 4 has been reported to give cyanoacetic acid as one of the principal oxidation products. Although good yields of acid were obtained under certain conditions, significant amounts of HCN were always formed as a side product. The electrochemical reduction of organic halides in CO 2 -saturated aprotic solvents has been extensively investigated as a synthetic route to carboxylic acids. 10-21 High faradaic and chemical yields were obtained when electrolyses were performed in undivided cells with sacrificial Al or Mg anodes. 10-12 Also catalytic systems, mainly based on transition-metal complexes, were employed with good results in either divided or undivided cells. 13-21 Two major reaction routes were identified in such catalytic processes. With some nickel, 13,15 palladium, 16 and cobalt 17-19 complexes, electrocarboxylation proceeds through involvement of metal-centered intermediates. In other systems the process is initiated by interaction between the reduced form of the mediator and RX whereby free radicals R " are formed...

Electrocarboxylation and related radical coupling processes of aryl and benzyl halides in microemulsion

“…Further improvements in the electrocarboxylation processes employing redox mediators [3][4][5] and silver cathodes [6,7] have been reported. Poly halogenated aromatic compounds [8], iodo aromatic compounds [9] and aliphatic halides [10,11] also undergo facile electrocarboxylation. Al 3?…”

Electrocatalytic carboxylation of chloroacetonitrile at a silver cathode for the synthesis of cyanoacetic acid

“…Indeed, we have previously demonstrated that the selectivity of the process at carbon cathodes depends essentially on the competition between these reactions [8,9]. • All homogeneous reactions take place within a thin strip of solution (denoted "reaction layer") adjacent to the electrode, whose thickness is vanishing small as compared to that of the diffusion layer, ı, whose size is fixed by the cell hydrodynamics.…”

“…The use of dangerous reagents such as cyanides makes this method of preparation an environmentally unfriendly process. For this reason, important research efforts have been carried out in the last 2 decades to find alternative methods using less dangerous reagents [2][3][4][5][6][7][8][9]. In particular, two electrochemical methods have recently been developed.…”

“…The best results, obtained with an experimental set-up using undivided cells equipped with sacrificial anodes, show Faradic yields lower than 30-40% [7]. The second is based on the cathodic reduction of NCCH 2 Cl at Hg [8] or carbon [8,9] cathodes in CO 2 -saturated aprotic solvents. This method gives good results both in terms of conversion and acid yields, but suffers from an inevitable employment of highly negative working potentials.…”

“…The mechanism of the electrochemical reduction of NCCH 2 Cl both in the absence and presence of CO 2 is well established [8][9][10]. The first step is a dissociative concerted electron transfer yielding a cyanomethyl radical and a chloride ion (Eq.…”