Thermodynamic Research On Phase Equilibrium In Spearation Of Nitro-o-toluidine Isomers Via Solvent Crystallization

4-Nitro-o-toluidine and 6-nitro-o-toluidine are all important intermediates of fine chemicals and dyes.They are widely used in organic synthesis,dipdye,rubber,pharmacy and other industries.At present,the industrial production method of 4-nitro-o-toluidine and 6-nitro-o-toluidine is using o-toluidine as a raw material via nitrification reaction,but this production method has low selectivity.The reaction provides as its product an isomeric mixtures of 4-nitro-o-toluidine and 6-nitro-o-toluidine.Solvent crystallization has the advantages of low energy consumption and easily operated,which can make up the shortcomings of the steam distillation technology.Solvent crystallization is based on solubility data,however,the solubility data of 4-nitro-o-toluidine and 6-nitro-o-toluidine is very scarce.In this paper,the binary and ternary solid-liquid equilibrium of different systems was studied.The results provide the basis for the separation processes of 4-nitro-o-toluidine and 6-nitro-o-toluidine.1.The solid-liquid phase equilibria of 4-nitro-o-toluidine in methanol,ethanol,n-propanol,isopropanol,n-butanol,ethyl acetate,aceton,acetonitrile,2-butanone,toluene and cyclohexane as well as the solubility data of 6-nitro-o-toluidine in methanol,ethanol,n-propanol,isopropanol,ethyl acetate,aceton,acetonitrile,1,4-dioxane,toluene and cyclohexane was measured by using isothermal dissolution method.The solubility of 4-nitro-o-toluidine and 6-nitro-o-toluidine increased with an increase temperature for a certain solvent.At the certain temperature,the mole faction solubility of 4-nitro-o-toluidine ranked as 2-butanone>acetone>ethyl acetate>acetonitrile>methanol>ethanol>n-propanol>n-butanol>isopropanol>toluene>cyclohexane and the mole faction solubility of 6-nitro-o-toluidine ranked as 1,4-dioxane>acetone>ethyl acetate>acetonitrile>toluene>n-propanol>ethanol>isopropanol>methanol>cyclohexane.Moreover,the solubility data was correlated by Apelblat model,Ah model,Wilson model and NRTL model.The maximum values of relative average deviation(RAD)and root-mean-square deviation(RMSD)acquired with the four models were no more than 2.44%and 49.86×10-4,respectively,and Apelblat model provided better results than the other three models.In addition,the solvent effect was discussed and the mixing Gibbs energy,mixing enthalpy,mixing entropy,activity coefficient at infinitesimal concentration and reduced excess enthalpy were calculated.2.The solid-liquid phase equilibria of 4-nitro-o-toluidine and 6-nitro-o-toluidine in binary(ethyl acetate + methanol),(ethyl acetate + ethanol),(ethyl acetate + n-propanol)and(ethyl acetate + isopropanol)solvent mixtures was measured by using isothermal dissolution method.The solubility of 4-nitro-o-toluidine and 6-nitro-o-toluidine increased with increasing temperature and mass fraction of ethyl acetate for the binary systems studied.And no solubilization phenomenon was found in the four binary systems.Moreover,The Jouyban-Acree model,van't Hoff-Acree model,Apelblat-Acree model,Sun model and Ma model were used to correlate the solubility data.The maximum values of relative average deviation(RAD)and root-mean-square deviation(RAMSD)acquired with the five models were no more than 0.63%and 4.06×10-4,respectively,and the Jouyban-Acree model gave best correlation results.In addition,the preferential solvation parameters of 4-nitro-o-toluidine and 6-nitro-o-toluidine in these four mixed solvents were caulated.In ethyl acetate(1)+ methanol(2)mixtures with composition O<x1<0.25(0.30),ethyl acetate(1)+ ethanol(2)mixtures with composition 0<x1<0.376,ethyl acetate(1)+ methanol(2)mixtures with composition 0<x1<0.434 and ethyl acetate(1)+ methanol(2)mixtures with composition 0<x1<0.216(0.45),the ?x1,3 value was negative indicating preferential solvation of solute by alcohol.In the other composition of ethyl acetate,the ?x1,3 value was positive indicating preferential solvation of solute by ethyl acetate.3.The solid-liquid phase equilibria for the ternary systems of 4-nitro-o-toluidine +6-nitro-o-toluidine + ethyl acetate at 293.15 K,303.15 K and 313.15 K and 4-nitro-o-toluidine +6-nitro-o-toluidine + toluene at 313.15 K,323.15 K and 333.15 K were measured by Schreinemaker's method,and the ternary phase diagrams were obtained.With the increase of temperature,the crystallization regions of the co-crystallization was decreased.The crystallization region of 4-nitro-o-toluidine was lager than that of 6-nitro-o-toluidine at a fixed temperature,especially in 4-nitro-o-toluidine + 6-nitro-o-toluidine + toluene system,and toluene was more conducive to the separation of nitro-o-toluidine isomers.In addition,the solubility data was correlated with the Wilson model and NRTL model.Compared with the results from the two models,the calculated solubility via the two models provided good agreement with the experimental values,which illustrated that two models colud all be used to corralate the 4-nitro-o-toluidine + 6-nitro-o-toluidine + ethyl acetate/toluene ternary system.