Measurement and correlation of solubility of 4-chloro-2,5-dimethoxynitrobenzene and 4-chloro-2,5-dimethoxyaniline in methanol, ethanol, xylene and toluene

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Highlights

  • Solubility of 4-chloro-2,5-dimethoxynitrobenzene in four solvents were measured.

  • Solubility of 4-chloro-2,5-dimethoxyphenylamine in four solvents were measured.

  • The experimental data were correlated with the Wilson model and the NRTL model.

  • A suitable solvent for reduction of 4-chloro-2,5-dimethoxynitrobenzene was suggested.

Abstract

The solubility of 4-chloro-2,5-dimethoxynitrobenzene (CDMB) and 4-chloro-2,5-dimethoxyaniline (CDMA) in methanol, ethanol, xylene and toluene was measured over the temperatures range from (278 to 338) K by the dynamic method using a laser monitoring observation technique. The solubility in all solvents increased with temperature and the greatest solubility of both systems was obtained in toluene. The Wilson and the NRTL models were applied to correlate the experimental results. The root-mean-square deviations for the system of (CDMB + solvent) ranged from T = (0.11 to 0.34) K and (0.08 to 0.33) K calculated by the Wilson and the NRTL models, respectively, while for the system of (CDMA + solvent) the root-mean-square deviations ranged from T = (0.11 to 0.32) K and (0.14 to 0.33) K. The melting points and enthalpies of fusion of CDMA and CDMB were determined by differential scanning calorimetry (DSC). Toluene was found to be the preferred solvent for the reduction of CDMB to CDMA from the point of view of reaction and product separation

Introduction

Compared to inorganic dyes, organic dyes have bright colours and powerful tinting strength. They can also play a protective role for products because of their unique structural features. According to their structures, organic dyes can be classified as azo, phthalocyanine, quinolone, etc. [1], [2]. The compound 4-chloro-2,5-dimethoxyaniline (CDMA, CAS No. 6358-64-1) is an important intermediate of azo dyes. It can be prepared for the Permanent Yellow HR (Colour Index No. CI Pigment Yellow 83 (2208)) and the Permanent pink FBB-B (Colour Index No. CI Pigment Red 146 (12485)) by diazotization reaction. Both dyes have a wide range of application in industry and they can be used for the colouration of superior ink, plastic, rubber, etc. with extremely good performance [3].

In the current industry production process of CDMA, hydroquinone is the main starting material, which is alkylated with dimethyl sulfate under alkaline conditions to prepare 1,4-dimethoxybenzene. Then 1,4-dimethoxybenzene is dissolved in 1,2-dichloroethane, reacts with sulfuryl chloride to prepare 2,5-dimethoxy-4-chlorobenzene [4], which is nitrated with dilute nitric acid to obtain 4-chloro-2,5-dimethoxynitrobenzene (CDMB, CAS No. 6940-53-0). Finally CDMB is reduced to obtain CDMA (the process is shown in figure 1) [5], [6].

Although the process of iron powder reduction CDMB is proven in industry, its energy consumption is high and the process is cumbersome. The process causes serious pollution to the environment due to the large amounts of iron sludge produced. With the increasingly stringent environmental requirements, the iron powder reduction process is being phased out gradually, and replaced by the clean, efficient and low-powered hydrogenation process [7], [8]. As can be seen from a previous paper [8], many organic reagents can be used as the solvent for the hydrogenation reaction, such as methanol, ethanol, toluene, xylene, etc. Meanwhile the solubility of CDMA in these solvents affects the separation and purification of the CDMA. However, no report about the solubility of CDMB and CDMA in these solvents could be found.

In this work, the solubility of CDMB and CDMA in methanol, ethanol, toluene and xylene has been measured by a dynamic method over the temperatures range from (278 to 338) K and ambient pressure. The Wilson and the NRTL models, which have been successfully used to describe the (solid + liquid) equilibrium (SLE) [9], [10], [11], [12], [13], [14], were employed to correlate the experimental results. The interaction parameters of the models were obtained. According to the solubility values obtained, the preferred solvent for the hydrogenation reaction of CDMB is suggested.

Section snippets

Experimental materials

The purchased CDMB was kept in the oven at T = 353.15 K to dry to constant weight before using. Since CDMA is easily oxidised in air, the sample of CDMA was dried in vacuum to a constant weight at temperature 353.15 K. The purities of CDMA and CDMB were determined by HPLC analysis. Other chemical reagents were used without further purification. The detailed information of the materials used in the experiment is listed in table 1.

Apparatus and procedure

The solubility was determined by the dynamic method [15]. The

(Solid + liquid) equilibrium equation

According to the thermodynamic description of SLE, the solubility equation is based on the equality of chemical potentials between components in all the coexisting phases. The SLE behaviour can be calculated by the following equation which involves the properties of the pure solute, such as enthalpy of fusion, melting point, etc. [9].lnx=-lnγ-ΔfusH/RTfusTfusT-1-1-ΔtrH/RTtrTtrT-1-1+ΔfusCp/RlnTTfus-1+TfusT-1-1.

Here x denotes the mole fraction of solute in the liquid phase, γ denotes the activity

Experimental results

The melting points of CDMB and CDMA measured by DSC are Tfus = (413.66 ± 0.11) K and (391.85 ± 0.08) K, respectively. The molar enthalpies of fusion of CDMB and CDMA by DSC are ΔfusH = (28.02 ± 0.45) kJ · mol−1 and (26.68 ± 0.36) kJ · mol−1, respectively. The numbers after symbol ± are the standard uncertainties which are calculated according to three times measurements with a level of confidence of approximately 68%. The melting point of CDMA is in good agreement with the data reported by Boehm Walter T = (392.15

Conclusions

The solubility of CDMB and CDMA in methanol, ethanol, xylene and toluene has been determined by the dynamic method within the temperature range from (278 to 338) K. Solubility of both compounds increases with the temperature in all solvents and the greatest solubility of both systems is obtained in toluene. The solubility results have been correlated by the Wilson and the NRTL models. Both the Wilson and the NRTL models can describe the systems well over the range of temperature and

Acknowledgments

The authors thank the support by the Program of Introducing Talents of Discipline to Universities, China, No. B06006.

References (27)

  • Q.B. Wang et al.

    Fluid Phase Equilib.

    (2005)
  • Q. Xia et al.

    Fluid Phase Equilib.

    (2011)
  • J.Y. Sun

    Fine Chem.

    (1997)
  • J.Y. Sun

    Chem. Ind. Eng.

    (1998)
  • D.T. Wang et al.

    Mater. Sci. Technol.

    (2005)
  • B.V. Tamhankar et al.

    Synth. Commun.

    (2001)
  • Y.Y. Song et al.

    Dyestuffs Colouration

    (2008)
  • W.D. Duan et al.
    (2012)
  • K. Warning, K. Habig, Process for the preparation 4-chloro-2,5-dimethoxy-aniline, US Patent 5,041,671,...
  • W. Bohm, 2,5-dimethoxy-4-chloroaniline, UK Patent 1,483,330,...
  • S.N. Chen et al.

    J. Chem. Eng. Data

    (2009)
  • H. Zhang et al.

    Ind. Eng. Chem. Res.

    (2013)
  • Q.B. Wang et al.

    J. Chem. Eng. Data

    (2007)
  • Cited by (0)

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