Measurement of acidity constants of benzothiadiazines by solvent extraction with use of a membrane phase-separator.
For extraction studies a "filter-probe" porous Teflon membrane phase-separator is used in conjunction with a spectrophotometer fitted with a small-volume flow-cell and a peristaltic pump to measure absorbance of the organic phase as a function of aqueous phase pH. Acidity constants of monoprotic (HA) and diprotic (H(2)A) acid benzothiadiazines have been measured with the apparatus. Accurate pK(a), values for these compounds are difficult to measure by other techniques. Mixtures of n-octanol and chloroform in various proportions can be used as the organic phase in order to adjust the distribution coefficient of the neutral species to give optimum precision and accuracy in measurement of the pK(a) values.
Khan
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AS
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada.
Cantwell
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FF