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Determination of purine bases. II. Argentometric determination of 6-mercaptopurine in the presence of certain other purine bases

K. Linek, C. Peciar, and M. Fedoroňko

Slovak Academy of Sciences, Bratislava

Abstract: cf. CA 58, 8409h. By potentiometric titration of a 0.2-0.6% aq. soln. of 6-mercaptopurine (I) in 0.2N H₂SO₄ with l. equiv. of 0.1N AgNO₃ an end point is observed; a 2nd end point is obtained slowly (heterogenous reaction with the Ag-I ppt.) by bringing the soln. to pH 9 with Na₂B₄O₇ and adding a further equiv. of AgNO₃. Hypoxanthine (II) and theophylline (III) react only in alk. medium consuming at pH 9, resp., 1.76 and 1 equiv. AgNO₃. These effects are used for the simultaneous detn. of the components of mixts. of I + II or I + III, with an accuracy of ±1%. By titrating I in acid medium the S--Ag insol. salt of I is formed at first and then at pH 9 a further equiv. of Ag substitutes the H of position 7; by titrating II at pH 9 both H atoms at positions 1 and 7 are substituted simultaneously by Ag. By supposing that the values of the soly. products of both Agmonosubstituted isomers of II are close, a plausible explanation is advanced for the observed decrease in AgNO₃ consumption to 88% of theory. 21 references.

Full paper in Portable Document Format: 177a510.pdf (in Slovak)

Chemical Papers 17 (7) 510–516 (1963)