| Methyl and nitro substituted benzoic acids are important chemical intermediates. They are used to prepare medicine and pesticides, such as:antihypertensive drug telmisartan, anticancer drug raltitrexed, cyantraniliprole and methoxyfenozide. Nowdays, the demand of these intermediates is growing rapidly, so the synthesis and separation of them is getting more attention.One of the preparation methods is w-toluic acid’s nitration reaction. The products are 3-methyl-4-nitrobenzoic acid,3-methyl-2-nitrobenzoic acid and 2-nitro-5-methylbenzoic acid. Similarly, the other reaction is 3-nitro-o-xylene’s oxidation reaction.3-nitro-o-xylene is oxidated into 2-methyl-3-nitrobenzoic acid and 3-nitrophthalic acid by the oxygen. The results of these two reactions are satisfied, while the process of separating the products need further study in industry. In generally, solvent crystallization is the better method to separate the similar mixture, as long as it has a difference between their solubility data in same solvents. This paper’s main content is the basic study of solvent crystallization and as follows:(1) The analysis method and the experimental apparatus were built. Then, the solubility data of 3-methyl-4-nitrobenzoic acid,3-methyl-2-nitrobenzoic acid, 2-nitro-5-methylbenzoic acid and m-toluic acid in pure solvents were measured at atmospheric pressure, respectively. The pure solvents were water, alcohols, acids, esters and acetone. It turned out that different solute had different solubilities in the same pure solvent. The modified Apelblat model was used to correlate the experiment data. The average relative deviations (ARD) were between 0.10%and 1.54%. It indicated that the calculated solubility data were in good agreement with experimental values. In order to understand the dissolution process of different solute in each solvent better, the thermodynamic parameters of solution such as dissolution enthalpy, dissolution entropy, Gibbs free energy, and isobaric heat capacity were obtained by the Clark-Glew equation and the parameters of Apelblat model.(2) The solubility data of 2-methyl-3-nitrobenzoic acid and 3-nitrophthalic acid in binary solvents were measured at atmospheric pressure by the same method, respectively. The binary solvents were acetic acid+water,3-nitro-o-xylene+water and methanol+water. It indicated that different solutes’solubilities were different in the same binary solvents. Then, the modified Apelblat model and NRTL model were used to correlate the experiment values, respectively. The average relative deviations (ARD) were all below 3.8%, which indicated the calculated data by the two models were in good agreement with experimental values. The effect of Apelblat model was better than NRTL model. What’s more, dissolution enthalpy, dissolution entropy, Gibbs free energy, and isobaric heat capacity were also obtained by the Clark-Glew equation and the parameters of Apelblat model.(3) In order to understand the solid-liquid equilibrium of the isomers, the latest progress was researched. Then, the modified UNIFAC model (Dortmund model) was used to correlate all the experiment values of 3-methyl-4-nitrobenzoic acid, 3-methyl-2-nitrobenzoic acid and 2-nitro-5-methylbenzoic acid in the pure solvents in two ways. The difference was two kinds of new groups. It was found that the second way could obtain the better correlation results. And the accuracy of the second way was well proved by the 2-methyl-3-nitrobenzoic acid’s solubilities in pure solvents. |
