Aqueous solution data five solvents

The rate of hydrolysis of propane sultone in aqueous solution is essentially independent of pH over the pH range 4-9, consistent with a BAL-E1 mechanism (equation 96). At higher pH values, however, in aqueous aprotic solvents the rate of hydrolysis increases and is attributable to an increasing contribution to the overall rate from concurrent bimolecular attack at sulphur (equation 97). Oxygen-18 tracer experiments confirmed that at pH >12, the hydrolysis of propane sultone proceeds with 14% sulphur-oxygen bond fission. The relative rates of hydrolysis at pH > 7 in 65% aqueous acetone of five-membered six-membered open-chain sulphonates (propane sultone, butane-1,4-sultone and of ethyl ethanesulphonate) were found to be 37 1 7126. The enthalpies of activation of all three compounds were very similar and the difference in rates were attributed to differences in entropies of activation ( — 17.1, —24.0 and —17.9 e.u., respectively). These data, however, are composite values. It is not possible to compare the kinetic acceleration for attack at sulphur in aliphatic sultones because both the six-membered sultone and the open-chain sulphonate hydrolyse exclusively with carbon-oxygen bond fission, within the limits of experimental detection. 

Since the presence of hydrogen atoms on the C" carbon atoms makes the nitroxides very unstable, experimental data are available for I and just in two solvents, CH2CI2 (14.9 G) [35a] and water (16.7) [35b]. If one assumes that for this compound the dependence of on the solvent parallels that determined for other five-membered nitroxides, fiom these two data we can extrapolate a solvent shift of about 2.5 G for the passage from the gas phase to an aqueous solution. The... 

Eq. (28) thus obtained can be used to represent the solubility of poorly soluble drugs in aqueous mixed solvents if information about the properties of the binary solvent (composition, phase equilibria and molar volume), the nonideality parameters and the constant A is available. These parameters can be considered as adjustable, and determined by fitting the experimental solubilities in the binary solvent. We applied such a procedure to the solubilities of caffeine in water/AW-dimethylformamide (Herrador and Gonzalez, 1997) and water/1,4-dioxane (Adjei et al., 1980), of sulfamethizole in water/1,4-dioxane (Reillo et al., 1995) as well as of five solutes in water/ propylene glycol (Rubino and Obeng, 1991). It was shown that Eq. (28) provides accurate correlations of the experimental data. 

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