Effects of some additives on proton-transfer reaction studied by ultrasonic methods.

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Ultrasonic absorption and velocity were measured in aqueous solutions of propylamine at 25 °C both in the absence and in the presence of 2 g dm−3 PVA(poly(vinyl alcohol)), 5 mol dm−3 urea and 1 mol dm−3 NaCl. No excess absorption was observed in these solutions without propylamine. A single relaxational absorption was observed in the concentration range from 0.0196 to 0.719 mol dm−3 of propylamine both in the presence and absence of the additives. The ultrasonic parameters have been found to be quite dependent on the concentration of propylamine and also on the structure of additives. This relaxational absorption has been attributed to the perturbation of an equilibrium associated with a proton-transfer reaction. The rate constants and the standard volume change of the reaction have been determined from the concentration dependences of the relaxation frequency and the maximum excess absorption per wavelength. As a result, it was discovered that the forward rate in a solution with PVA increased and those with urea and NaCl, on the other hand, decreased; also, the standard volume change associated with the reaction increased in a series of the solutions with urea, no additive, NaCl, and PVA. The data have been interpreted by means of the structural changes of the solvent water.
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