On the electroreduction mechanism of α-haloketones

The electrolytic reduction of phenacyl chloride 3, phenacyl bromide 4, 4-(chloroacetyl)pyridine 6 and 4-(bromoacetyl) pyridine 7 was investigated and compared to that of the analogous ketones acetophenone 5 and acetyl pyridine 8] and halides (2-chloroethyl)benene 9 and (2-bromoethyl)benzen 10]. Current-potential curves on mercury were measured and the products from preparative electrolyses were isolated and identified. The α-haloketones exhibited two reduction waves, the less negative of which corresponded to the cleavage of the CX bond while the other was due to the reduction of the resulting ketone. The α-haloketones in general were found to be more reactive than the analogous halides and this effect was even more pronounced in the pyridine derivatives. A mechanism involving addition of an electron to an orbital delocalized over the carbonyl and the halogen is suggested, to account for this phenomenon.