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

Aqueous solutions of antipyrine and its derivatives. I. Heats of solution

F. Kopecký, M. Hollá, and J. Čelechovský

Department of Physical Chemistry, Faculty of Pharmacy, Komenský University, Bratislava

Abstract: The integral heats of soln. ΔH₂ of antipyrine (I), 4-methylantipyrine (II), 4-aminoantipyrine (III), and aminopyrine (IV) in H₂O were measured with a calorimeter at 25° at the largest possible concns. The differential heats of soln. ̅L₂ and diln. ̅L₁ were detd. from the concn. dependence ΔH₂. Except for IV, ΔH₂ and ̅L₂ of I, II and III are pos. but substantially decrease with diln. In the case of IV, ΔH₂ is already neg. and it decreases further on diln. ̅L₁ is therefore neg. in all cases. The excess enthalpies of the dissolved substances were calcd. from the measured ΔH₂  and ̅L₂ values by applying the known values of the heats of melting. The excess enthalpy values, approx. -3 to -7 kcal./mole, and their concn. dependence together with ̅L₁ values confirm the high hydration of the investigated substances. The exothermic character of the interactions with H₂O increases in the order: II < III < I < IV. The interactions of these compds. with H₂O are hindered by the Me and the primary amino group in the α-position to carbonyl of the pyrazolone ring, and they are considerably increased by the tertiary amino group (IV).

Full paper in Portable Document Format: 219a666.pdf (in Czech)

Chemical Papers 21 (9) 666–675 (1967)