Ionization constant organic-water mixed solvents

We have recently devised a rapid and convenient method for determination of the ionization constant for water in mixed aqueous organic solvents (11-16). The method utilizes glass electrodes and gives results in satisfactory agreement with earlier work. 

Incidentally, such plots (Figure 4) may be used to compute approximate values of the bulk dielectric constants of water-organic mixed solvents from the emf measurements provided that the bulk dielectric constant is higher than 40. In fact, for auto-ionizing solvents this may be a convenient method, and our calculations have shown that such computed values are within 5-7% of the experimental values. 

Computation of the Ionization Constant of Weak Monoprotic Acids in Water—Organic Mixed Solvents... 

The ionization constant of HBrOs in formamide has been determined at 25, 30, and 35 °C from solubility measurements. The polarographic behaviour of BrOj in mixed solvent systems containing water and an organic solvent (e.g. formamide, MeCN) is essentially the same as the behaviour in neutral or alkaline aqueous media.Isotope exchange induced by 7-irradiation between Br and BrOs in aqueous solution at room temperature is essentially complete.The rate of exchange was found to be first-order with respect to both dose rate and [BrO ]. 

Peters JJ, Determination of ionization constants in mixed aqueous solvents of varying composition by a single titration, /. Pharm. Sci., 67,127-129 (1978). NB The paper recognizes riie problem of long extrapolations from aqueous-organic solvent mixtures to estimate pXa values of poorly water-soluble substances. No activity corrections were applied. See Cinnarizine for further details. 

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