(1) The electrolytic reduction potentials of ketonic compounds such as diacetyl, acetoin, acetone, methylethylketone, acetophenone, benzophenone, benzil, benzoin were measured with the dropping mercury cathode and the polarograph.
(2) In order to show the relation of reduction potentials of these compounds to their concentrations and hydrogen ion concentrations, the so-called theoretical values were calculated by the Nernst formula of the reversible reduction type, and were compared with the observed values at 25°C.
π=-0.05911/2logk'/?H?²?reducible compounds?
3) For diacetyl, if the R. P. (-0.345 V) (from In calomel electrode) of the 1.13•10^-3mol in (O.Oln HCl+O.ln KCl) solution was taken as a standard, we found
log k'=4.681
The observed reduction potentials showed relatively small deviations from the calculated values in the acidic solutions, but in the alkaline solutions the observed R. P. were more positive than the calculated R. P.
(4) In the case of acetone, logk'=34.911, and the R. P. (obs.) showed much larger negative deviations and could not be regarded as reversible.
For methyl ethylketone logk'=34.418, that is to say, methylethylketone is more easily reducible than acetone, although their difference is not conspicuous.
(5) For acetoin, logk'=30.453, and the deviation from the calculated values were about the same magnitudes as in the case of acetone.
(6) For acetophenone logk'=28.235.
(7) In the cases of benzophenone, benzil and benzoin, a certain amount of ethyl alcohol was added to the electrolysing solution, and as the ethylalcohol was found to make the reduction potential negative, we did not calculated log k'.
We may say from the results of the experiments that the reduction po-tentials of aromatic ketones showed much smaller deviations than those of aliphatic ketones and that the reductions of the aromatic ketones have a reversible character, although the present authors have the view that there seems to be no definite difference or discontinuity between reversible and irreversible reductions. In the alkaline solutions the R. P. of aromatic ketones showed larger deviations than in the acidic, and moreover, the direction of the deviations were reversed, that is, the R. P. (obs.) in alkaline solutions were much positive than the R. P. (calc.)
Further, the polarograms of aromatic ketones showed typical saturation curves, while those of the' aliphatic ketones were slowly increasing and did not show definite saturation curves. So we may say, that a minute quantity of an aromatic ketone in a solution may more easily determinable by the polarographic method than an aliphatic ketone.
(8) The solubility at 25°C of the following compounds in water were determined by the polarographic method.
Benzophenone 4.41.10^-4g. mol, per liter.
Benzil 8.86.10^-5g. mol. per liter.
Benzoin 1.51•10^-4g. mol. per liter.
(9) The group effects of CH₃, C₆H₅, CO, OH on the reducibility of ketone radical are noteworthy.
If we compare the reduction potentials of the solutions, containing about 10^-4 mol. of reducible substances in (O.Oln HCl+0.ln KCl) mixture, we reach the following.
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As is seen in the above table, the differences of the compounds R•CO•CO•R are
Acetone and Diacetyl -0.876 V
Benzophenone and Benzil -0.610 V
Those of R•CO•R and R•CO•H(OH)•R are
Acetone and Acetoin -0.139 V
Benzophenone and Benzoin -0.060 V
The C₆H₅ group makes CO more easily reducible than CH₃ group as the following
Acetone and Acetophenone -0.162 V
Acetophenone and Benzophenone -0.103 V
The substitution of two CH₃ and C₆H₅ makes reduction potential about 0.2 Volts

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