The spectrophotometric determination of the pKa of pyrrolidinedithiocarbamic and piperidinedithiocarbamic acids, based on diode array measurements

Abstract

A spectrophotometric method, based on the use of a diode array spectrophotometer, is proposed in order to determine the pKa of pyrrolidinedithiocarbamic (HPyr-I) and piperidinodithiocarbamic (HPip-II) acids. The high speed of data acquisition of the equipment made it possible to minimize the problem of acid decomposition. The values obtained were 3.10(I) and 3.51(II) in I = 0.50 mol L-1 (NaClO4) at 25.0°C, and are consistent with the acid decomposition mechanism. A discussion is presented based on the shape of the compound spectra in acidic and basic media and their relation to the order of the pKa values for I and II.