抄録
(1) The reduction potential of nicotinic acid was measured with the dropping mercury cathode and the polarograph.
(2) Two stages of the reduction process were observed.
(3) For the first stage of reduction, observed R-P. was compared with the theoretical value calculated by the following formula at 15°C.,
π=-0.05713/2logk'/?H.?2CC5H4N•COOH in which by taking the R. P. of 0.01 mol nicotinic acid in (0.01n HCl+0.1n KCl) solution, i.e. -0.984V as a standard, we have
log k=28.33
In an acidic as well as in a neutral salt solution, the observed R. P. showed satisfactory concordance with the calculated values, and thus the first stage has been concluded to be the reduction of the carbonyl group of nicotinic acid to aldehyde.
(4) The second stage of reduction is considered to be the reduction of pyridine ring of nicotinic acid, by comparison with the R. P. of pyridine in our preceding paper.
(5) The reduction of nicotinic acid in an excess of alkali, does not take place, owing, perhaps, to the desorption of negatively charged nicotinic acid ions to the polarised mercury cathode. R. P. in a sodium acetate or sodium bicarbonate solution was about 0.02V more negative than the calculated value.
(6) Maximum of current voltage curve was observed in sodium bicar-bonate solution, in which the potential of maximum current intensity was almost independent of the concentration of nicotinic acid.
(7) The reduction potential of benzoic acid was studied for the sake of comparison, with the result that in hydrochloric acid, no reduction but only the deposition of hydrogen ion has been seen, while a potassium chloride solution the R. P. is over 0.240V negative than that of nicotinic acid. Thus the group effect of a carbonyl group is considered to be more effective than a benzene ring.
(8) The decisive conclusion as to the reduction process has been left out for the time, when the isolation of the reduction product, now under investigation, would be completed.
