Electrolysis of Trichlomethylated Compound Under Aerobic Condition Catalyzed by B12 Model Complex

Reductive dehalogenation reactions are presently of great interest, primary because of their potential use in the treatment of halogenated solvent wastes as well as in remedial approaches to remove such chemicals from contaminated soils.  A Co(I) species of cobalamin emerged in the active site of B12-dependent enzyme is a supernucleophile and reacts with an alkyl halide to form an alkylated complex with dehalogenation.  Thus, the superior ability of cobalamin for reductive dehalogenation prompted us to investigate the catalysis of a cobalamin derivative for degradation of various halogenated compounds such as 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT), perchloroethelene (PCE), chloroform and so on.    

     Electrolysis of such organic halides mediated by cobalt complex usually achieved in anaerobic condition to avoid loss of reactive Co(I) species by autooxidation.  Carbon center radical formed by homolysis of cobalt-carbon bond in alkylated complex generally coupled to form dimerized compound or abstract hydrogen to form simply reduced product.  Here we reported electrolysis of organic halide under aerobic condition and conducted the reaction of in-situ generated substrate radical with oxygen to form more valuable compound such as ester.  

    Electrolysis of trichloromethyl benzene at -0.9 V vs. Ag/AgCl in the presence of heptamethyl cobyrinate perchlorate (1) in ethanol under anaerobic condition using undivided cell equiped with Pt mesh cathode and Zn plate anode to yield Z and E forms of 1,2-dichlorostilbene with 49% and 7%, respectively.  In contrast, the same reaction was carried out in an aerobic condition, ethyl benzoate was selectively produced in 61 % yield based on initial concentartion of substrate.  When the electrolysis was carried out in methanol or isopropano, methyl benzoate and isopropyl benzoate were formed, respectively.  As for mechanism, primary formed radical species from homolysis of alkylated complex may reacts with oxygen to form peroxy species.  Homolysis of O-O bond of peroxy species should produce oxyl radical.  Following disproportionation and isomerization may produce benzoyl chloride as key intermediate in this reaction.  Reactive benzoyl chloride could reacts with solvent ethanol to yield ethyl benzoate.  Application of this aerobic electrolysis with colalamin derivative toward various trichloromethylated compounds will be reported.