ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Oscillopolarographic determination of reaction kinetics of alkaline hydrolysis of the tropane-group alkaloids

G. Dušinský

National Institute for Medical Drugs Control, Bratislava

Abstract: The majority of alkaloids, even the nonreducible ones, yielded in alk. soln. a cathodic spike caused by capacity effects. Owing to alk. hydrolysis, alkaloids of the tropane group showed a decrease with time in the depth of the spike until it disappeared completely. The oscillopolarographic method was suitable for measuring the rate of the hydrolysis. Atropine, homatropine, scopolamine, and cocaine were investigated. The decrease of the depth of the spikes with time was detd. for different concns. of OH^- ions and at various temps. The concn. of alkaloids was 5 × 10^-5M; the depth of the spike was a linear function of concn. From the relation of the depth of the spike to time, the apparent consts. of hydrolysis were calcd. and their log.-log. plot vs. OH^- ion concn. was a straight line with a slope of 1. The catalytic rate consts. of the alk. hydrolysis were: atropine 0.0051, scopolamine 0.017, homatropine 0.027, and cocaine 0.037 l./mole/sec. (20°). From the temp. dependence, the values of the exptl. Arrhenius activation energy and the frequency factor of the alk. hydrolysis were calcd. The different rates of hydrolysis were in agreement with the structures of the alkaloids. The greater rate of the hydrolysis of homatropine as compared with atropine is due to the inductive effect of the electroneg. OH^- group of the mandelic acid. The accelerating effect of the ethylene oxide group in scopolamine is of steric nature. The disappearance of the capacity spikes of tropane alkaloids is caused by alk. hydrolysis, which can be measured by oscillographic polarography.

Full paper in Portable Document Format: 1411-12a764.pdf (in Slovak)

Chemical Papers 14 (11-12) 764–773 (1960)