The solubility of ammonium chloride in acetonitrile, dioxane, and 2-propanol in the range 298.153338.15 K was determined using 36 Cl tracer. The influence of properties of nonaqueous solvents on the solubility of ammonium, potassium, and sodium chlorides was subjected to thermodynamic and correlation analysis. The low solubility of ammonium chloride in dioxane and acetonitrile is due to the endothermic effect, and its high solubility in 2-propanol, to the exothermic effect of the salt solution. The entropy of solution affects the solubility of ammonium chloride in acetonitrile only slightly, in contrast to dioxane and 2-propanol in which the entropies of solution are significant and have opposite signs. The solubility of ammonium and potassium chlorides depends on the electron-acceptor power of the solvents and electrostatic interactions in solution, whereas the solubility of sodium chloride in organic solvents is determined by the combined influence of the donor3acceptor and dielectric properties of the solvents.The standard thermodynamic characteristics of solution and solvation of electrolytes reflect the total effect from the ion3solvent and solvent3solvent interactions. The ion3solvent interactions involve the following effects [1]: polarization of the medium; changes in the solvent structure; creation of a cavity in the solvent for accommodation of the dissolved ion; specific interactions of ions with solvent molecules (hydrogen bonding, donor3acceptor interactions).Our goal was to study the thermodynamics of solution of ammonium chloride in dioxane, acetonitrile, and 2-propanol and to examine the solvent effects on the solubility of ammonium, sodium, and potassium chlorides in nonaqueous solvents by methods of correlation and regression analysis, based on the experimental results obtained and on the published data. The solubility of ammonium chloride in dioxane, acetonitrile, and 2-propanol in the range 298.153 338.15 K was determined using 36 Cl tracer. The labeled salt NH 4 36 Cl was prepared by ion exchange of ammonium chloride with H 36 Cl. The total error of the radiometric measurement results was evaluated according to GOST (State Standard) 8-207376 [2]. The solubilities L in nonaqueous solvents at 298.153338.15 K, calculated as arithmetic mean values of separate determinations at a confidence level of 0.95, are listed in Table 1. The confidence interval [D a = +t a sn 31/2 , where t a is Student's coefficient; s, rms deviation of the solubility; n, number of samples taken (no less than 18)] for theH 4 Cl solubility is +(6 0 10 36 3 0.001) M depending on the solvent and temperature. The values by which the solubility in the examined solvents varies with temperature (DL T ) exceed the error of L determination: dL T is 21.5 0 10 35 in dioxane, 3.2 0 10 34 in acetonitrile, and 4.0 0 10 33 M in 2-propanol (Table 1).With increasing temperature, the salt solubility in nonaqueous solvents increases. The coefficients of the temperature dependence of the NH 4 Cl solubility in nonaqueous solvents, ln L = a + b...
The solubility of N- [4-(difluoromethylthio)phenyl]-2-aminobenzoic acid in the system water3 1,2-propanediol was studied over the entire range of the concentrations of the mixed solvent at 288.153 328.15 K.Anthranilic acid derivatives are commonly used in modern pharmacology. N-[4-(Difluoromethylthio)-pheny]l-2-aminobenzoic acid (Difluorant, hereinafter DF), a nonsteroid antiphlogistic with antipsoriasis activity, is among them.Difluorant is a hydrophobic organic compound, sparingly soluble in water, which makes it difficult to create on its basis water-containing medicines in the form of ointments, foams, and emulsions. Therefore, a study of the DF solubility in nonaqueous solvents, which can homogenize hydrophobic and hydrophilic compounds and their mixtures with water, is one of the main stages of development of highly effective and inexpensive drugs. The most commonly used solvent in soft medicines is 1,2-propanediol (1,2-PD) [1].This study is concerned with the DF solubility in the water31,2-PD system over the entire range of the concentrations of the mixed solvent at 288.153 328.15 K. EXPERIMENTALThe water31,2-PD system was prepared gravimetrically. 1,2-Propanediol was preliminarily treated by double vacuum distillation [2]. The quality of 1,2-PD was checked by the density (r 4 25 = 1032.8 kg m !3 ) and dielectric permittivity (e = 29.0 at 25oC). As second component was used double-distilled water. Prior to use, DF was dried for 2 h at 353 K under a pressure of 2.7 kPa. The quality of the preparation was checked by the melting point (T m = 397 K).The DF solubility was studied by the isothermal method, and the concentration of the saturated solution was determined by the electronic spectroscopy. To do this, excess amount of the substance under study was placed in flasks with ground-glass stoppers, the solvent of the required composition was added, and the mixture was kept at a constant temperature controlled to within + 0.1 K with continuous agitation until the thermodynamic equilibrium was attained. The attainment of the equilibrium was monitored by taking the solution samples and measuring their optical density. The equilibrium was assumed to be attained when the optical density A of a series of successively taken solution samples became constant. Then, the solutions were allowed to settle for 33 4 h at the given temperature, after which they were sampled for the analysis. The saturation time was from 10 to 100 h, depending on the concentration of the nonaqueous component.The optical density A was measured on a Specord M-40 spectrophotometer at l = 310 nm. To do this, 2 ml of the transparent saturated solution was diluted with ethanol so that A of the solutions obtained was within 0.33 0.7. Each value of the solubility is the average of 33 4 measurements. The maximum average error in determining the solubility was 233% at a confidence probability of 0.95. The results obtained are presented in the table.Our results show that the DF solubility varies within a wide range depending on the solvent composition a...
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