Solubility of phenobarbital, salicylic acid, and caffeine in a mixture of 12 kinds of solubilizing agent and water was measured, and the relationship between the solubility and dielectric constant was examined. In a mixed solvent of water and ethylene glycol, diethylene glycol, or triethylene glycol, possessing only a hydrophilic group, a plot of dielectric constant against the logarithm of solubility expressed by molar fraction gave a straight line, and it would be difficult to consider that these solubilizing agents undergo association in the mixed solvent. In contrast, in the mixed solvent of water and cellosolve, carbitol, dipropylene glycol, methylcarbitol, or 1-methoxy-2-propanol, which possess both hydrophobic and hydrophilic groups, the same plot gave one flexion in the straight line, indicating that these solubilizing agents undergo association at a specific concentration, some kind of a sudden change occurs in the internal structure of the mixed solvent, and a change in the solubility of phenobarbital and salicylic acid occurs at this concentration, and a maximum solubility in caffeine. Further, in the mixed solvent of water and butylcellosolve, butylcarbitol, hexylene glycol, or isopropylcellosolve, there were two flexions in the straight line, suggesting that these solubilizing agents undergo stronger association.
抄録全体を表示