Solubility of Various Barbiturates in Buffered Aqueous Solutions I. Test of a Theoretical Equation

Abstract

The solubility of 10 variously substituted barbiturates [5,5''-diethylbarbituric acid; 5-ethyl, 5-phenyl barbituric acid, 5-ethyl, 5-isoamyl barbituric acid; 5-ethyl, 5-(1-methylbutyl) barbituric acid; 5-ethyl, 5-butyl barbituric acid; 5-ethyl, 5-isopropyl barbituric acid; 5-ethyl, 5(1-methyl propyl) barbituric acid; 5-ethyl, 5(1-methyl-butenyl) barbituric acid; 5,5-diethyl, 1-methyl barbituric acid and 5-ethyl, 5(1-methylbutyl) thiobarbituric acid] were determined in 2 pH buffered solvent systems at 3 temperatures. The buffer systems chosen were pH values at the pKa of these solutes and at .apprx. 3 pH units below the pKa, producing undissociated solute molecules and equimolar concentrations of the acid form and dissociated salt form, respectively. The solubility values obtained experimentally were tested against a theoretical analytical expression that relates the solubility at pH values above the solubility of the undissociated form. There was some adherence to this equation with deviations reported.