Acid-base equilibria in ethylene glycol--I: definition of pH and determination of pk-values of acid-base indicators.
A pH-scale in ethylene glycol is defined, based on potentiometric measurements for a cell without liquid junction: glass electrode || 0.1M (HCl + KCl), ethylene glycol | AgCl:Ag; and a potentiometric-spectrophotometric method for the determination of pK-value of acid-base indicators in ethylene glycol on the basis of this pH scale is proposed, in which the pH scale is established and the pK-value determined in a single titration at constant ionic strength. The following pK-values of indicators are reported: Cresol Red-3.00, Thymol Blue-3.39, Bromophenol Blue-6.49, Bromocresol Green-7.38, Bromocresol Purple- 9.00 and Cresol Red (2nd change)-11.07. A linear relationship was found between the pK-values of four sulphonphthalein indicators in ethylene glycol and in water according to the following equation (pK(HI)(c))(EG) = 2.3 + 1.1 (pK(HI)(c))(W). An attempt is made to explain this dependence, based on the idea of solute-solvent interaction of species of the same charge type.
Zikolov
P
P
Faculty of Pharmacy, Academy of Medicine Ekz. Josif No. 15, Sofia, Bulgaria.
Budevsky
O
O