J. Segretario, P. Zuman
Dec 10, 1986
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0
Influential Citations
11
Citations
Journal
Journal of Electroanalytical Chemistry
Abstract
Abstract Polarographic reduction of the symmetrical diprotonated form of 1-phenyl-1,2-propanedione (I) occurs in waves i′1 and i1 at pH The latter can be further reduced at more negative potentials in waves i4 and i5. At pH 8.5 to 9.5 the asymmetrical monoprotonated form of I is reduced in the irreversible wave i2 directly to α-ketol which is electroinactive under conditions used. At pH > 9.5 the symmetrical unprotonated form is reversibly reduced into enediolate dianion. Base catalyzed conversion of the enediolate into electroinactive species causes the decrease of the anodic wave obtained with the Kalousek commutator method at pH > 11. The ratio [α-ketol]:[β-ketol] under polarographic conditions is kinetically controlled, while during controlled potential electrolysis it is thermodynamically controlled. The diketo form of compound I is present in about 60% in the monohydrated form. Acid catalyzed dehydration results in an increase in wave i′1 in acidic media, base catalyzed in an increase in wave i3 at pH > 9. The overall pKa-value of the diprotonated form is pKH12 = −1.0, that of the geminal diol dissociation is pKOH = 10.35 and that corresponding to carbanion-enolate formation is pKB = 11.6. Possibility of separation of individual pK-values is shown and assumptions on which such separation is based are stated.