Ethyl acetate-calcium chloride system, methanol

A method of prediction of the salt effect of vapor-liquid equilibrium relationships in the methanol-ethyl acetate-calcium chloride system at atmospheric pressure is described. From the determined solubilities it is assumed that methanol forms a preferential solvate of CaCl296CH OH. The preferential solvation number was calculated from the observed values of the salt effect in 14 systems, as a result of which the solvation number showed a linear relationship with respect to the concentration of solvent. With the use of the linear relation the salt effect can be determined from the solvation number of pure solvent and the vapor-liquid equilibrium relations obtained without adding a salt. 

Figure 7. Result of prediction for methanol-ethyl acetate-calcium chloride system at 1 atm (O), observed (—), calculated.

The author selected the system containing salt which is not dissolved with other components but only with a particular component of a solvent mixture as a system with which the phenomenon of preferential solvate can be understood easily. Calcium chloride is dissolved with alcohol but it is not dissolved well with ester. Thus, calcium chloride forms a preferential solvate with alcohol and does not with ester. For the component system which consists of calcium chloride, alcohol, and ester, the author selected the following three systems for which vapor-liquid equibrium relations have been measured methanol-ethyl acetate-calcium chloride (I) methyl acetate-methanol-calcium chloride (3) and n-butyl acetate-n-butanol-calcium chloride (3). 

The preferential solvation formed between salt and solvent molecules causes a salt effect on vapor-liquid equilibria. A method of prediction of salt effect based on the preferential solvation number was reported previously for the case in which salt was solved below the saturation level. The idea introduced in this chapter applies for salt solved in saturation. The alcohol-ester-calcium chloride system for which the preferential solvation was thought to be formed was examined. Specifically, calcium chloride dissolves readily in alcohol but only sparingly in ester. Thus, when calcium chloride is solved into alcohol-ester mixed solvent, the calcium chloride will form a preferential solvation with alcohol only. Methanol-methyl acetate, butanolr-butyl acetate, and methanol-ethyl acetate systems were selected for the mixed-solvent systems. 

The salt effect in the MeOH-EtOAc-CaC system can be explained by preferential solvation. As calcium chloride dissolves readily in methanol but only sparingly in ethyl acetate, it will be sufficient to consider the interaction between methanol molecules and calcium chloride molecules only in the MeOH-EtOAc solution. Referring again to Figure 2, the free methanol molecules which are not clustered with ethyl acetate increase linearly when the liquid-phase composition of methanol is above 0.333 in mole fraction. The solubility... 

The salt effect is attributable to the formation of preferential solvation from the standpoint of molecular structure. In other words, when calcium chloride, which dissolves readily in methanol but very little in ethyl acetate, was added to the methanol-ethyl acetate system to saturation, calcium chloride formed with methanol the preferential solvate which may be written CaCl2 6CH30H. It was also shown from the observation of solubility that the solvated methanol molecules did not participate in the vapor-liquid equilibrium. 

Figures 7, 8, and 9 indicate the prediction results for the following three systems methanol-ethyl acetate, methyl acetate-methanol, and butyl acetate-butanol with saturated calcium chloride, respectively. The absolute value of mean errors At/ were 0.018 and 0.014 for each system, while the maximum and minimum errors were 0.047 and 0, 0.039 and 0.005, and 0.039 and 0.005, respectively.

Under the protection of nitrogen, the compound 3.6 (166 mg, 0.5 mmol) was dissolved in methanol (5 mL), and then, calcium chloride (222 mg, 2 mmol) was added at room temperature. The reaction was stirred at room temperature for 0.5 h and then cooled to 0 °C. Sodium boron hydride (46 mg, 1.2 mmol) was added, and the reaction was stirred for 1.5 h at 0 °C. TLC showed that the reaction was completed. Water (2 mL) was added slowly at 0 °C to quench the reaction. The reaction system was hltered and diluted with ethyl acetate (50 mL), washed with saturated sodium bicarbonate (3 x 50 mL), and the aqueous phase was extracted with ethyl acetate (100 mL), washed with saturated brine (40 mL). The combined organic phase was dried over Na2S04 and hltered and the solvent was removed by rotary evaporator. The resulting crude product was purihed by hash silica gel column chromatography (EtOAc/hexane = 1 3) to give 160 mg colorless liquid (Rf= 0.50, EA/HA = 1 4), yield 95 %. 

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