Second-stage dissociation of N,N-bis(2-hydroxyethyl)-2-amino-ethanesulfonic acid ( bes) in water + 10, + 30, and + 50 mass per cent tetrahydrofuran from 278.15 to 328.15 K

Abstract

The second-step thermodynamic dissociation constants of the zwitterionic form of bes, a useful secondary-standard biological buffer, have been determined at 278.15 to 328.15 K in 10, 30, and 50 mass per cent of tetrahydrofuran ( thf) + water solvent mixtures. E.m.f. measurements of (hydrogen + silver bromide) cells without liquid junction have been made at intervals of 5 K for the process bes ±(S) = bes −(S) + H +(S). The values of p K 2 are given as a function of T by the equation: pK 2 = 2706.4( K T ) − 6.7375 + 0.16112( T K ) for 10 mass per cent: pK 2 = 2069.1( K T ) − 2.4673 + 0.0088648( T K ) for 30 mass per cent; and pK 2 = 763.87( K T ) + 5.7135 − 0.0033996( T K ) for 50 mass per cent of thf. The results are compared in terms of standard Gibbs free energies, enthalpies, and entropies of transfer, from water to 50 mass per cent methanol + water, 2-methylpropan-2-ol + water, and thf + water.