Electrochemical Oxidation of Metals in Alcohols

Many metals can be transformed into alkoxides by relatively simple procedmes of anodic oxidation in alcohol-based media. A thermostated electrochemical cell without subdivision of cathodic and anodic space is used as reaction vessel. The process is nm with direct current, using for regulation of voltage the same potentiostat equipment that is common for biochemical electrophoresis experiments. The reaction proceeds in conditions close to equilibrium (if 3 V) only for the late transition metals, for example, Cu, Co, and Ni [81], and involves complexation with the anions of electrolyte at the anode and formation of the alkoxide via metathesis at the cathode  

The alkoxides of these elements are insoluble in the reaction medium and their separation by precipitation drives the process to desired products. 

The mechanism of the reaction for early transition elements is considerably different, involving direct nonequilibrium oxidation of both alkoxide and electrolyte (chloride or bromide) anions at the anode. The reaction is most facile in alcohols with higher electric conductivity (methanol and functional amino- or alkoxyalcohols). 

Because the process is associated with the breakdown of an oxide barrier layer at the anode, it requires usually impressively high voltage (30-200 V). The products of electrochemical synthesis are always contaminated with halides and, for early transition elements, also with bimetallic alkoxides with Li when lithium salts are used as electrolytes. It means that the products after separation need to be purified by additional recrystallization or distillation. High-yield electrochemical synthesis has been proved to be an attractive approach to such precursors as Nb(OMe)s [96], Ta(OMe)s [104], MoO(OMe)4 [117], WO(OMe)4 [117], Mo (OMe)6 and W(OMe)6 [118], and Re406(0Me)12 [60]. 

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