Solubility of 2-nitro-p-phenylenediamine in nine pure solvents and mixture of (methanol + N-methyl-2-pyrrolidone) from T = (283.15 to 318.15) K: Determination and modelling

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Highlights

Abstract

By using the isothermal saturation method, the solid-liquid equilibrium of 2-nitro-p-phenylenediamine in pure organic solvents of methanol, ethanol, n-propanol, isopropanol, N-methyl-2-pyrrolidone, acetonitrile, ethyl acetate, toluene and 1,4-dioxane and liquid mixture of (N-methyl-2-pyrrolidone + methanol) was obtained experimentally at the temperatures ranging from (283.15 to 318.15) K under atmospheric pressure, and the solubility of 2-nitro-p-phenylenediamine in the selected solvents was determined by a high-performance liquid chromatography (HPLC). Within the studied temperature range, the 2-nitro-p-phenylenediamine solubility in mole fraction in these solvents increased with increasing temperature. The descending order of the mole fraction solubility in pure solvents was as follow: (N-methyl-2-pyrrolidone, 1,4-dioxane) > ethyl acetate > acetonitrile > methanol > ethanol > n-propanol > isopropanol > toluene, and for the (N-methyl-2-pyrrolidone + methanol) mixture with given initial composition, the mole fraction solubility of 2-nitro-p-phenylenediamine increased with increasing temperature and mass fraction of N-methyl-2-pyrrolidone. The values of solubility for 2-nitro-p-phenylenediamine in pure solvent were correlated and calculated with the modified Apelblat equation, λh equation, Wilson model and NRTL model; and in the binary solvent mixture of (N-methyl-2-pyrrolidone + methanol), the Jouyban–Acree model, modified Apelblat–Jouyban–Acree model and Sun model. For the pure solvents, the largest values of the relative average deviation (RAD) and root-mean-square deviation (RMSD) obtained by the four models were 1.17% and 6.80 × 10−4, respectively; and for (N-methyl-2-pyrrolidone + methanol) mixture, they were a larger, which were 3.59% and 19.12 × 10−4. In general, the selected thermodynamic models were all acceptable for describing the solubility behaviour of 2-nitro-p-phenylenediamine in the solvents. In addition, the mixing properties including the mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient at infinitesimal concentration (γ1) and reduced excess enthalpy (H1E,) were calculated for 2-nitro-p-phenylenediamine in pure solvents. Knowledge of the solubility and thermodynamic studies is essential in optimizing the purification process of 2-nitro-p-phenylenediamine.

Introduction

Nitroanilines are used extensively as vital intermediates representing an attractive target for organic synthesis. They are important intermediates for dyes, pharmaceuticals and agrochemicals owing to their inherently reactive nature as highly versatile synthons [1]. 2-Nitro-p-phenylenediamine (CAS REG No. 5307-14-2) is used in semi-permanent and permanent (oxidative; tinting colour) hair dye formulations [2]. In the field of pharmaceutical industry, 2-nitro-p-phenylenediamine is used as an initial raw material to prepare ilaprazole and ezogabine [3], [4]. Several literatures have reported the synthetic methods of 2-nitro-p-phenylenediamine [1], [5], [6], [7], [8], [9], [10]. Selective catalytical hydrogenation of 2,4-dinitroaniline to obtain 2-nitro-p-phenylenediamine has attracted much attention in recent years [1], [6], [7], [8], [9]. The synthesis route is shown in Fig. 1. During the synthesis process of 2-nitro-p-phenylenediamine, it is inevitably accompanied by the formation of by-product 4-nitro-o-phenylenediamine. The mixed products of 2-nitro-p-phenylenediamine and 4-nitro-o-phenylenediamine should be separated before further reaction and preparation of single pure compound. Thus, it is a necessary step to separate the mixture of 2-nitro-p-phenylenediamine and 4-nitro-o-phenylenediamine from the isomer mixtures in industry. However no separation method has been proposed in the previous publications.

The solvent crystallization is commonly used as a crucial separation and purification step. The solubility of solid compound in solvents plays an important role for understanding the (solid + liquid) phase equilibrium (SLE) in the development of a crystallization process. Solvent crystallization is an effective method for 2-nitro-p-phenylenediamine purification. In order to obtain high purity product, the knowledge of solubility of 2-nitro-p-phenylenediamine in various solvents at elevated temperatures is a critical step. Moreover, thermodynamic properties of solution are always design foundations of chemical separation which can also improve the purity and yield of 2-nitro-p-phenylenediamine. To the best of the authors’ present knowledge, it is unfortunate that no solubility values have been reported in the previous works.

The purification of 2-nitro-p-phenylenediamine is often made in organic solvents. From many species of organic solvents, we choice nine commonly used organic solvents (methanol, ethanol, n-propanol, isopropanol, N-methyl-2-pyrrolidone, acetonitrile, ethyl acetate, toluene and 1,4-dioxane) in industrial purification process. The objectives of this work are to (1) determine the solubility of 2-nitro-p-phenylenediamine in the nine pure solvents and binary solvent mixture of (N-methyl-2-pyrrolidone + methanol) at temperatures ranging from (283.15 to 318.15) K under atmosphere pressure; (2) correlate the solubility values using the modified Apelblat equation, λh equation, Wilson model and NRTL model; and (3) calculate the mixing properties for the solution process of 2-nitro-p-phenylenediamine in different solvents. Specifically, the temperature of solvent-assisted crystallization of 2-nitro-p-phenylenediamine is almost within the temperature range from 280 K to 320 K, so the selected temperatures lie the range from T = 283.15 K to T = 318.15 K.

Section snippets

Solubility models

With the intention of finding an appropriate equation or model to describe the solubility behaviour of 2-nitro-p-phenylenediamine in the selected solvents and achieve further application for the obtained solubility data, in this work, four thermodynamic models, modified Apelblat equation [11], [12], λh equation [13], Wilson model [14] and NRTL model [15] are employed to correlate the solubility of 2-nitro-p-phenylenediamine in pure solvents; and Jouyban–Acree model [16], modified

Materials and apparatus

2-Nitro-p-phenylenediamine was provided by Beijing HWRK Chemical Co., Ltd, China with a mass fraction of 0.983. It was recrystallized three times in ethanol. The final 2-nitro-p-phenylenediamine used in experiment had a purity of 0.996 in mass fraction, which was confirmed by a high-performance liquid phase chromatograph (HPLC, Agilent-1260). The selected solvents, such as methanol, ethanol, n-propanol, isopropanol, N-methyl-2-pyrrolidone, acetonitrile, ethyl acetate, toluene and 1,4-dioxane

Properties of pure substance

The DSC scan of 2-nitro-p-phenylenediamine is shown in Fig. 3. Based on the DSC analysis, the melting temperature Tm and melting enthalpy ΔfusH of 2-nitro-p-phenylenediamine are 411.35 K and 16.40 kJ·mol−1, respectively. The value of Tm determined in this work is lower than that reported in Ref. [24], and higher than those determined in Refs. [6], [26], but within the range determined by Burgdorf [25]. The deviations may be due to the difference in equipment, samples and (or) measured conditions.

Conclusion

The mole fraction solubility of 2-nitro-p-phenylenediamine in nine pure solvents including methanol, ethanol, n-propanol, isopropanol, N-methyl-2-pyrrolidone, acetonitrile, ethyl acetate, toluene and 1,4-dioxane and in (N-methyl-2-pyrrolidone + methanol) solvent mixtures was determined experimentally with the isothermal saturation method at the temperatures ranging from (283.15 K to 318.15 K) under 101.2 kPa. The mole fraction solubilities of 2-nitro-p-phenylenediamine increased with increasing

Acknowledgment

This work was financially supported by the National Natural Science Foundation of China (Project number: 21406192), the Natural Science Fund for Colleges and Universities in Jiangsu Province (Project number: 14KJD530002) and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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