Solubility measurement and thermodynamic functions of 3-nitrobenzaldehyde in different solvents at elevated temperatures

Highlights

• Solubility of 3-nitrobenzaldehyde in twelve solvents were determined.

• The solubility were correlated with four thermodynamic models.

• Mixing properties of the solutions were computed based on NRTL model.

Abstract

The solubility was measured for 3-nitrobenzaldehyde in methanol, ethanol, isopropanol, n-butanol, acetonitrile, acetone, ethyl acetate, toluene, N,N-dimethylformamide, acetic acid, cyclohexane and n-propanol by using a high-performance liquid chromatography analysis under pressure of 101.2 kPa. The temperatures of solubility determination were from (273.15 to 303.15) K. The mole fraction solubility of 3-nitrobenzaldehyde increased with the increase in temperature, and obeyed the following order from high to low in different solvents: N,N-dimethylformamide > (acetone, acetonitrile) > ethyl acetate > toluene > methanol > acetic acid > ethanol > n-propanol > n-butanol > isopropanol > cyclohexane. Four models, modified Apelblat equation, λh equation, Wilson model and NRTL model were employed to correlate the experimental mole fraction solubility. The largest root-mean-square deviation (RMSD) was 6.98 × 10⁻³, and the largest relative average deviation (RAD) was 1.93% for each set of solubility results. On the whole, the calculated solubility values were in good agreement with the experimental results for the four selected models, and the NRTL provided the best results. Moreover, the mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient at infinitesimal concentration (${\gamma }_1^{\infty }$) and reduced excess enthalpy ($H_1^{\text{E,}\infty }$) were computed based on the NRTL model. The experimental solubility, thermodynamic models and thermodynamic properties are very important in the purification process of isomeric mixtures of nitrobenzaldehydes.

Introduction

3-Nitrobenzaldehyde (CAS Reg. No: 99-61-6) is pale yellow crystal with molar mass and molecular formula of 151.12 g·mol⁻¹ and C₇H₅NO₃, respectively. Its chemical structure is shown in Fig. 1. 3-Nitrobenzaldehyde is an important pharmaceutical intermediate and has achieved industrial importance for the synthesis of various pharmaceutical intermediates [1], [2], [3], [4], [5]. In recent years, some methods for 3-nitrobenzaldehyde production have been put forward in the literature [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. In general, it can be synthesized by using benzaldehyde [6], [7], [8], [9], [10], [11], [12], [13], [14] or 3-nitrotoluene [15] or 3-nitrophenol [16] as the raw materials. The main production method for 3-nitrobenzaldehyde is nitration of benzaldehyde by using mixed nitric acid and sulphuric acid [6], [7], [8], [9], [10], [11], [12], [13], [14]. This method of making nitrobenzaldehydes results in mixtures of the isomers. The crude product containing isomers limits its further use in various areas.

There are several ways known for separating the isomeric mixtures of nitrobenzaldehydes. They can be separated by an adsorption–desorption process [17], [18], [19], distillation process [20], extraction process [21] and chemical conversion process [22], [23]. The decomposition temperature is so near the distillation temperature, for safety reasons, the distillation method is ruled out. Moreover, the high boiling points make separation by distillation energy-intensive. Fractional crystallization is not satisfactory because the melting points are very close (2-: 42–44 °C; 3-: 58 °C). Indirect methods, e.g., conversion of the isomers into acetals, which can be separated by distillation, and then converted back into the nitrobenzaldehyde [23]. So, a method of separating the isomers directly, avoiding costly chemical conversions and reconversion, is still desired.

Solvent crystallization is an important step that determines the quality of the product of 3-nitrobenzaldehyde with low cost and high efficiency. Solubility is an essential physicochemical property that plays an important role in solvent crystallization process. Therefore, it is very significant to know the solubility of 3-nitrobenzaldehyde as a function of temperature in different solvents. For the purification of the desired nitrobenzaldehyde, recrystallization from organic solvents can be undertaken [21]. Recently, we report the solubility of 4-nitrobenzaldehyde in some pure organic solvents [24]. Nevertheless, to the best of authors’ present knowledge, no study has been made for determining and correlating the solubility of 3-nitrobenzaldehyde in the open publications.

From many species of organic solvents, we select twelve commonly used organic solvents (methanol, ethanol, isopropanol, n-butanol, acetonitrile, acetone, ethyl acetate, toluene, N,N-dimethylformamide, acetic acid, cyclohexane and n-propanol) he in industrial purification process. In order to enrich our knowledge of the solubility and provide fundamental basis for separating the three isomers, the main objectives of this work are to (1) determine the solubility of 3-nitrobenzaldehyde in the selected solvents over the temperature range from (273.15 to 303.15) K under atmosphere pressure; (2) correlate the obtained solubility with different solubility models; and (3) evaluate the thermodynamic properties for the solution process of 3-nitrobenzaldehyde in the selected solvents.