A Simple and Practical Theoretical Model for Interpreting Binary Azeotropes

We put forth a simple and yet practical theoretical model generalized from Raoult’s law and Henry’s law and show that it can be reduced to these two laws under limiting conditions. The model entertains a hybrid parameter h_B with activity coefficient bundled into it, which smoothly bridges the p_B^* and K_B coefficients in Raoult’s law and Henry’s law. The value of h_B falls in the interval of [K_B, p_B^*] or [p_B^*, K_B] in the case of negative or positive deviation from Raoult’s law, respectively. We uncover an overlapping rule for the ranges of h_A and h_B, which binary mixtures must obey to form azeotropes. We also provide straightforward ways to analyze the characteristic mole fraction and pressure for azeotropes and to understand the relative positions of vapor composition curves with respect to the liquid counterparts. We rely heavily on experimental data available in the literature for representative binary mixtures with both negative and positive deviations from Raoult’s law to illustrate the algebraic derivations. The knowledge gained is useful in the analysis of experimental data from vapor-liquid equilibrium measurements and possess pedagogical merit in various relevant fields.

A Simple and Practical Theoretical Model for Interpreting Binary Azeotropes

We put forth a simple and yet practical theoretical model generalized from Raoult’s law and Henry’s law and show that it can be reduced to these two laws under limiting conditions. The model entertains a hybrid parameter h_B with activity coefficient bundled into it, which smoothly bridges the p_B^* and K_B coefficients in Raoult’s law and Henry’s law. The value of h_B falls in the interval of [K_B, p_B^*] or [p_B^*, K_B] in the case of negative or positive deviation from Raoult’s law, respectively. We uncover an overlapping rule for the ranges of h_A and h_B, which binary mixtures must obey to form azeotropes. We also provide straightforward ways to analyze the characteristic mole fraction and pressure for azeotropes and to understand the relative positions of vapor composition curves with respect to the liquid counterparts. We rely heavily on experimental data available in the literature for representative binary mixtures with both negative and positive deviations from Raoult’s law to illustrate the algebraic derivations. The knowledge gained is useful in the analysis of experimental data from vaporliquid equilibrium measurements and possess pedagogical merit in various relevant fields.

The Composition of Saturated Vapor over 1-Butyl-3-methylimidazolium Tetrafluoroborate Ionic Liquid: A Multi-Technique Study of the Vaporization Process

A multi-technique approach based on Knudsen effusion mass spectrometry, gas phase chromatography, mass spectrometry, NMR and IR spectroscopy, thermal analysis, and quantum-chemical calculations was used to study the evaporation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4). The saturated vapor over BMImBF4 was shown to have a complex composition which consisted of the neutral ion pairs (NIPs) [BMIm+][BF4−], imidazole-2-ylidene C8N2H14BF3, 1-methylimidazole C4N2H6, 1-butene C4H8, hydrogen fluoride HF, and boron trifluoride BF3. The vapor composition strongly depends on the evaporation conditions, shifting from congruent evaporation in the form of NIP under Langmuir conditions (open surface) to primary evaporation in the form of decomposition products under equilibrium conditions (Knudsen cell). Decomposition into imidazole-2-ylidene and HF is preferred. The vapor composition of BMImBF4 is temperature-depended as well: the fraction ratio of [BMIm+][BF4−] NIPs to decomposition products decreased by about a factor of three in the temperature range from 450 K to 510 K.

Polymorphic Crystallization Design to Prevent the Degradation of the β-Lactam Structure of a Carbapenem

The cooling crystallization of carbapenem CS-023 was performed at 25 °C in an aqueous solution. Tetrahydrate crystals (form H) were obtained. Hydrate crystals are promising drugs, but there has been problems in manufacturing such crystals. During cooling crystallization, a dissolution process at a high temperature of 70 °C was utilized. The main problem in manufacturing was that the degradation rate of CS-023 at 70 °C was high, as expressed in the half-life period of 2.97 h. Poor solvent crystallization using ethanol was observed at 25 °C. Thus, a different polymorph (Form A) was obtained. Form A comprised CS-023, 5/2 ethanol, and 1/2 H2O. Form A, containing ethanol, is not suitable as a drug. Form A was then transformed to another polymorph of hydrate crystals or tetrahydrate Form H. Another hydrate polymorph, Form B, was obtained through the solid phase transformation of Form A and further transformed to the tetrahydrate Form H, at high humidity over 80% RH. This process, which proceeded at the low temperature of 25 °C, helped to prevent the degradation of CS-023, thereby avoiding wastage. Furthermore, the solid-phase transition could be controlled with vapor composition.