Branched-chain mechanism in electrolytical reduction of some aryl alkyl ketones on mercury electrodes
✍ Scribed by J. Volke; A. Ryvolová-Kejharová; O. Manoušek; L. Wasilewski
- Book ID
- 104148777
- Publisher
- Elsevier Science
- Year
- 1971
- Weight
- 619 KB
- Volume
- 32
- Category
- Article
- ISSN
- 0022-0728
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✦ Synopsis
In the course of the last twenty years both simple aryl alkyl ketones and those substituted with various groups have been the subject of polarographic investigation from various points of view 1-7. Elving and Leone 5 found that in acetophenones with a halogen (chlorine or bromine) substituent on the benzene nucleus only the carbonyl group is reduced; this happens at less negative potentials than with unsubstituted acetophenone. On the other hand, if the halogen atom is located in the methyl group of acetophenone, first the C-X bond is reduced at more positive potentials and, only at more negative potentials, the reduction of the carbonyl group takes place. This also holds true in the case of e-fluoroacetophenone 4 where, after electrolysis at the potential of the limiting current of the first wave, fluorides were found in the solution. This has been, as yet, the only example of the polarographic reduction of a C-F-bond. The difluoromethyl and trifluoromethyl groups are not reducible. A similar reduction mechanism to that in e-halogenoacetophenones was also found by Lund 6 in some other e-substituted acetophenones and butyrophenones where first the substituent is split off, and only at more negative potentials is the resulting acetophenone or butyrophenone reduced. In butyrophenones carrying a substituent on the 7-carbon of the aliphatic chain, the substituent is not reduced, and only the reduction of the carbonyl group may be affected by its presence. Some derivatives of p-fluorobutyrophenone belong to modern psychotherapeutics 8. We have described a method for their analytical determination by means of polarography in a recent paper 9. The aim of the present communication is to investigate the effect of the bulky heterocyclic substituent on the reduction of the carbonyl group and to make a comparison with p-fluorobutyrophenOne and butyrophenone-as well as with their lower homologues--, and to determine accurately by coulometry the number of electrons consumed in the reduction. EXPERIMENTAL Polarographic curves were recorded by means of a polarograph LP 60 (Laboratorni p?istroje, Praha) with a pen-recorder EZ 2. Polarographic electrolysis was carried out in a Kalousek cell with a separated calomel electrode (SCE) and an H-cell according to Manou~ek with a SCE separated by a saturated KC1 bridge. All values of half-wave potentials are expressed versus a SCE, the potential of which