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Dissociation Constants and Solubilities of Dalbergin and Nordalbergin in Different Solvents
The dissociation constants (p<i>K</i><sub>a</sub>) of
dalbergin and nordalbergin were measured at 298.2 K using ultraviolet
(UV) spectroscopy method. The solubilities of dalbergin and nordalbergin
in water, methanol, propanone, ethyl ethanoate, trichloromethane,
and hexane have been determined by the UV spectrophotometric method
from 283.2 to 308.2 K at atmospheric pressure. The experimental solubility
values were correlated with a modified Apelblat equation, λ<i>h</i> model, and ideal model. The p<i>K</i><sub>a</sub> value of dalbergin is 8.91 ± 0.12, and the p<i>K</i><sub>a1</sub> and p<i>K</i><sub>a2</sub> values of nordalbergin
are 7.31 ± 0.29 and 9.79 ± 0.39, respectively. The solubilities
of dalbergin and nordalbergin in six solvents increase with an increase
in temperature. The solubility order of dalbergin in six pure solvents
was trichloromethane > propanone > ethyl ethanoate > methanol
> hexane
> water, whereas that of nordalbergin was propanone > methanol
> ethyl
ethanoate > trichloromethane > water > hexane. A comparison
of the
solubility of dalbergin with that of nordalbergin shows that the 7-methoxyl
moiety of dalbergin leads to a significantly higher solubility in
trichloromethane and hexane, a little higher solubility in ethyl ethanoate,
an approximately equal solubility in propanone, and a little lower
solubility in methanol and water (exception 283.2 K). For dalbergin,
the modified Apelblat equation shows the best correlation for all
solvents, and for nordalbergin, correlation results by three models
are similar