RESEARCHES ON THE ELECTROLYTIC REDUCTION POTENTIALS (PART V)

ON THE REDUCTION POTENTIALS OF KETONIC RADICALS AND THEIR RELATION TO THE CHEMICAL CONSTITUIONS (CONTINUED)

抄録

(1) The reduction potentials of acetylacetone, acetonylacetone, benzoylacetone, dibenzoylmethane and diphenyltriketone 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 socalled theoretical values of R. P. were calculated by the Nernst formula of the reversible reduction type assuming two atoms of hydrogen taking part in the reduction, and were compared with the observed values at 25°C
π=0.05911/2logk'/[H'][Reducible compound]
EXPERIMENTS.
(3) Results of one part of the experiments were given in Fig. 5 (in original paper) showing PH reduction potential curves.
(4) For acetylacetone, taking the reduction potential (-1.097 V) of 1.033•10^-2 molar solution in the mixture as a basis of a calculation we found
logk'=31.09
For acetonylacetone
logk'=32.94
(-1.152 V for 1.0 10^-3 molar solution in the mixture [0.01 n HCl 0.1 n KCl]) For benzoylacetone
logk'=22.70
(-0.901 V for 1.0 10^-3 molar solution in the mixture [0.01 n HCl 0.1 n KCl]) For benzoylmethane
log k'=22.90
(-0.887 V for 1.0 10^-3 molar solution of 50% alcoholic medium [0.01 n HCl 0.1 n KCl]) For diphenyltriketone,
logk'=2.46 (-0.311 V for 1.0•10^-3 molar 10% alcoholic solution of 0.1 n NH₄Cl)
(5) 1-3 diketone, such as acetylacetone, benzoylacetone, dibenzoylmethane showed two distinct reduction potentials, due to enol- and ketoforms of these compounds. Further their enol forms were always more reducible than their ketoform.
(6) The negatifying effect of ethyl alcohol to the reduction potential of benzoylacetone was tested with the result that their R. P. changes linearly with the alcoholic concentration.
(7) The solubility of benzoylacetone to water was calculated to be 2.36×10^-3 mol per liter at 25°C.
(8) The group and orientation effects on the reduction potentials of ketonic compounds were found as the following.
1, 2 diketones were more reducible than 1, 3 diketones, for example:
Diacetyl and acetylacetone 0.802 V
Benzil and dibenzoylmethane 0.616 V
1, 3 diketone was more reducible than 1, 4 diketone, although the difference was much less conspicuous than the former cases.
Acetylacetone and acetonylacetone 0.055 V
Substitution of methyl group with phenyl group made R. P. more positive as mentioned in Part IV of our papers.
Benzoylacetone and acetylacetone 0.264 V
Dibenzoylmethane and acetylacetene 0.385 V
With regard to 1, 2 diketone and 1, 2, 3, triketone, contrary to our expectation, the former was more reducible than the latter, for example.
Benzil was more reducible than diphenyltriketone. This is much noticeable as diketones were far more reducible than monoketone as was reported in our previous paper.