| 3-Nitrosalicylic acid and 5-nitrosalicylic acid are important intermediates in organic synthesis areas,They are widely used in chemical,pharmaceutical,liquid crystal,agricultural and other industries and play a significant role in chemical production and drug synthesis.Nowadays,3-nitrosalicylic acid and 5-nitrosalicylic acid are mostly produced by nitration of salicylic acid in industry but for the low selectivity.While most of 5-nitrosalicylic acid is obtained,a small amount of 3-nitrosalicylic acid is produced as by-product.Also,the nitrosalicylic acid isomers are difficult to separate by means of distillation operation due to their similar physicochemical properties,especially the boiling point.They can be effectively separated by solvents crystallization.Solvent crystallization as a low-energy separation method can effectively compelete the unsolvable problems of distillation,extraction and adsorption and obtain green safe separation.In this dissertation,the binary and ternary solid-liquid equilibrium of different systems was studied.The results provide the basis for the separation processes of nitrosalicylic acid isomers.The equilibrium solubilities of 3-nitrosalicylic acid and 5-nitrosalicylic acid in methanol,ethanol,n-propanol,isopropanol,n-butanol,isobutanol,ethylene glycol(EG),ethyl acetate,acetonitrile,N-methyl-2-pyrrolidinone(NMP),N,N-dimethylformamide(DMF),1,4-dioxane and water were measured by using isothermal dissolution method.The solubility of nitrosalicylic acid isomers increased with a rise of temperature,and obeyed the sequence from high to low in different solvents for 3-nitrosalicylic acid at the certain temperature:NMP>DMF>ethyl acetate>methanol>ethanol>n-propanol>acetonitrile>isopropanol>n-butanol>isobutanol>EG>1,4-dioxane>water and the mole faction solubility of 5-nitrosalicylic acid ranked as NMP>(DMF,1,4-dioxane)>acetonitrile>methanol>ethanol>isopropanol>n-propanol>ethyl acetate>n-butanol>isobutanol>EG>water.Moreover,the obtained solubility values were correlated by the modified Apelblat model,λh model,NRTL model and Wilson model.The maximum values of relative average deviation(RAD)and root-mean-square deviation(RMSD)acquired with the four models were no more than 4.20%and 40.23×10-4,respectively,and the modified Apelblat model provided better results than the other three models.In addition,the solute-solvent and solvent-solvent interactions was studied based on the KAT-LSER equation.Meanwhile,the mixing properties of 3-nitrosalicylic acid and 5-nitrosalicylic acid in pure solvents were calculated.The equilibrium solubilities of nitrosalicylic acid isomers in(methanol+water),(n-propanol+water),(acetonitrile+water)and(DMF+water)solvent mixtures were measured by using isothermal dissolution method.The solubility of 3-nitrosalicylic acid and 5-Nitrosalicylic acid increased with increasing temperature and decreasing mass fraction of water for the binary systems studied and no solubilization phenomenon was found during entire experiments.Moreover,the Jouyban-Acree model,Van’t Hoff-Jouyban-Acree model,Apelblat-Jouyban-Acree model and Sun model were used to correlate the solubility data that obtained the corresponding model parameters.The RAD and RMSD were no more than 3.97%and 27.33×10-4,respectively,and the Jouyban-Acree model achieved best correlation results.In the meanwhile,the standard enthalpy of dissolution and transfer properties of 3-nitrosalicylic acid and 5-nitrosalicylic acid in mixed solvents were calculated.The solid-liquid phase equilibria of 5-nitrosalicylic acid+3-nitrosalicylic acid+methanol and 5-nitrosalicylic acid+3-nitrosalicylic acid+ethyl acetate at 288.15 K,298.15 K and 308.15 K were measured by Schreinemaker’s method,and the ternary phase diagrams were obtained.The co-crystallization regions were decreased with increasing temperature.The crystallization region of 5-nitrosalicylic acid was lager than that of 3-Nitrosalicylic acid at a given temperature,especially in 5-nitrosalicylic acid+3-nitrosalicylic acid+ethyl acetate system,and ethyl acetate was more faviourable in separation of nitrosalicylic acid isomers.In addition,the solubility data was correlated with the NRTL model and Wilson model.The RMSD were 7.500×10-3 and 7.869×10-3 respectively,the RAD were 2.054×10-2 and 2.790×10-2 respectively,which illustrated that the NRTL model colud corralate the 5-nitrosalicylic acid+3-nitrosalicylic acid+methanol/ethyl acetate ternary systems accrurately. |
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