Acid-base equilibria in γ-butyrolactone studied by use of pH-ISFETs

Abstract

pH-ISFETs were used in the study of acid-base equilibria in γ-butyrolactone (GBL). After the spectrophotometric determination of the p K a value of 3,5-dichloropicric acid, the p K a values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta 2O 5-type pH-ISFET. The values of p K a in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in p K a between GBL and PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si 3N 4-ISFET, was about 30 on the p K SH scale. A comparative study was made of the response speeds of the Ta 2O 5- and Si 3N 4-type pH-ISFETs and a conventional pH-glass electrode. The result was Si 3N 4-ISFET > Ta 2O 5-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional glass electrode.