Initial Oxidation Potential Research Articles

Anodic oxidation of β-cyanoethyl ethers

Anodic oxidation of β-cyanoethyl ethers ROCH 2CH 2CN (R = Me, Et, t-Bu, CH 2CH 2CN) has been performed in 1.6 M H 2SO 4, using platinum and lead dioxide as anode materials. The main products were cyanoacetic acid (CEA) and the acid corresponding to R (formic acid for R = Me, acetic acid for R = Et). In the case of R = Et (EPN), HAc was found with current efficiencies up to 81% (at low conversions), while CEA was generated with relatively low ces up to 34%. Kinetic curves for EPN exhibit an early appearance of β-oxypropionitrile (OPN), the intermediate to CEA, and acetaldehyde. Thus, the -CH 2 group of Et is primarily attacked to yield the semiacetal in a two-electron oxidation, which is rapidly cleaved in acid solutions to yield the above-mentioned intermediates. HCN found as a side product is derived from anodic attack at the -CH 2 group adjacent to the cyano group, leading to the readily saponified cyanohydrin. The ether reacts in the adsorbed state. This leads to large positive potential shifts and unusual Tafel slopes of 240–300 mV decade −1 due to only partial efficiency of Galvani voltage. Moreover, a partial coverage of Pt electrode with PtO x has been detected even in the presence of the ether. Coincidence of PtO x-potential and initial oxidation potential of ether leads to the proposal of a mechanism in terms of redox catalysis. It has been found in addition, that diethyl ether is oxidized to HAc in high yields. Thus, our new findings are not restricted to β-cyanoethyl ethers.