SECOND DISSOCIATION-CONSTANTS OF 3-(CYCLOHEXYLAMINO)-1-PROPANESULFONIC ACID (CAPS) AND 3-(CYCLOHEXYLAMINO)-2-HYDROXY-1-PROPANESULFONIC ACID(CAPSO) FROM THE TEMPERATURES 278.15-K TO 328.15-K

The second dissociation constant pK(2) values for 3-(cyclohexylamino)- 1-propanesulfonic acid (CAPS) and 3-(cyclohexylamino)-2-hydroxy-1-prop anesulfonic acid (CAPSO), useful secondary standard buffers within the pH range of 9.7 to 10.5 for CAPS, and 8.9 to 10.0 for CAPSO, have bee n determined from T = 278.15 K to T = 328.15 K. Electromotive force me asurements of cells of the type: Pt\H-2 (g,p degrees = 101.325 kPa)\bu ffer (m(1)), Na salt of buffer (m(2)), NaCl (m(3))\AgCl\Ag, where m de notes molality, were used. The pK(2) for the ionization of CAPS in the experimental temperature range is expressed by the equation: pK(2) = 1046.64.(K/T) + 35.10191 - 4.9342.ln(T/K), whereas that for CAPSO is g iven by: pK(2) = 2106.21.(K/T) + 9.08772 - 1.11049.ln(T/K). The thermo dynamic quantities have been calculated and the results obtained are c ompared with those for zwitterionic compounds which are the derivative s of taurine. (C) 1997 Academic Press Limited.