Solubility determination and thermodynamic modelling of 3,5-dimethylpyrazole in nine organic solvents from T = (283.15 to 313.15) K and mixing properties of solutions

doi:10.1016/j.jct.2017.02.011

The Journal of Chemical Thermodynamics

Volume 110, July 2017, Pages 99-109

https://doi.org/10.1016/j.jct.2017.02.011 Get rights and content

Highlights

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3,5-Dimethylpyrazole Solubility in nine pure solvents were determined.
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The solubility was regressed by the modified Apelblat equation, λh equation, Wilson model and NRTL model.
•
The mixing properties were calculated.

Abstract

Solubility of 3,5-dimethylpyrazole in nine organic solvents including ethanol, isopropanol, n-propanol, 1-butanol, methanol, ethyl acetate, toluene, acetone, acetonitrile was determined experimentally by using the isothermal saturation method over a temperature range from (283.15 to 313.15) K under 101.3 kPa. For the temperature range studied, the solubility of 3,5-dimethylpyrazole in the solvents increased with a rise of temperature. In general, they obeyed the following order from high to low in different solvents: 1-butanol > n-propanol > (ethanol, isopropanol, methanol, ethyl acetate, acetone) > toluene > acetonitrile. The acquired solubility data of 3,5-dimethylpyrazole in the studied solvents were correlated by using the modified Apelblat equation, λh equation, Wilson model and NRTL model. The maximum values of root-mean-square deviation (RMSD) and relative average deviation (RAD) were 3.293 × 10⁻³ and 2.62%, respectively. The RAD values acquired with the modified Apelblat equation were smaller than those with the other three models for a certain solvent except for the system of n-propanol. Generally, the four thermodynamic models were all acceptable for the systems of 3,5-dimethylpyrazole in these solvents. Furthermore, the mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient at infinitesimal concentration ( $γ_{1}^{\infty}$ ) and reduced excess enthalpy ( $H_{1}^{E, \infty}$ ) were obtained. The solution process of 3,5-dimethylpyrazolewas spontaneous in the studied solvents. The obtained solubility and thermodynamic studies would be very helpful for optimizing the purification process of 3,5-dimethylpyrazole.

Graphical abstract

Introduction

3,5-Dimethylpyrazole (CAS No. 67-51-6, its chemical structure is in Fig. 1) is an important fine chemical products with high added value. It was recently used as the ligand to study the synthesis and structure of trimethylacetato complexes of zinc [1], copper [2], nickel [3], and cobalt [4]. And more, 3,5-dimethylpyrazole has been found to be a most satisfactory reagent for the gravimetric determination of cobalt [5]. As a hypoglycemic agent, 3,5-dimethylpyrazole was found to be fifty-four times more potent orally than tolbutamide in glucose-injected, fasted intact rats [6]. In addition, the use of 3,5-dimethylpyrazole as blocking agents for isocyanates is known [7]. With 3,5-dimethylpyrazole blocked lacquer polyisocyanates can be used as crosslinkers in high-quality one-component polyurethane coating binders. The advantage of 3,5-dimethylpyrazole to other blocking agents such as butanone oxime is in a much lower thermal yellowing of the coatings and a relatively low firing temperature of about 130 °C [8]. Several methods have been proposed to produce 3,5-dimethylpyrazole in the literature [9], [10], [11], [12], [13]. However, all these kinds of method contain some unreacted reactants and a large amount of side products (i.e. C₇H₁₇N₃ radical dot HNO₃, CAS No. 1924673-14-2; C₁₈H₁₁N₃O₄S, CAS No. 1773542-01-0, et al.). With the expansion of ligand and hypoglycemic agent in industrial applications, the requirement for product purity is becoming higher. The crude 3,5-dimethylpyrazole restricts its applications in many aspects. The by-products must be removed from the crude product before use.

It is well-known that the solubility data play an important role in optimizing the crystallization procedure and improving the purity and yield of 3,5-dimethylpyrazole. Therefore, it is necessary to know the solubility of 3,5-dimethylpyrazole in different solvents at various temperatures. More particularly, the knowledge of accurate solubility is needed for the design of crystallization process. In previous publications, the purification method of 3,5-dimethylpyrazole is recommended via a sublimation and petroleum ether [14]. Although the solubility data are of great significance in the purification procedure of 3,5-dimethylpyrazole via the method of solvent crystallization where the accurate solubility values of 3,5-dimethylpyrazole are essential, to the best of the authors’ present knowledge, no solubility data are reported in the previous works. In order to acquire high purity 3,5-dimethylpyrazole, the knowledge of 3,5-dimethylpyrazole solubility in different solvents at various temperatures and the thermodynamic properties of solution is a necessary procedure.

The purposes of the work are to (1) determine the solubility of 3,5-dimethylpyrazole in ethanol, isopropanol, n-propanol, 1-butanol, methanol, ethyl acetate, toluene, acetone, acetonitrile at temperatures ranging from (283.15 to 313.15) K by using the isothermal saturation method; (2) correlate the solubility data with different thermodynamic models; and (3) calculate the mixing properties for the solution process of 3,5-dimethylpyrazole in different solvents.

Section snippets

Solid-liquid phase equilibrium models

In order to find suitable models to describe the solubility behavior of 3,5-dimethylpyrazole in the studied solvents, in this work, four models are used to correlate the solubility data, which correspond to the modified Apelblat equation [15], [16], $λ h$ equation [17], Wilson model [18] and NRTL model [19].

Materials and apparatus

The 3,5-dimethylpyrazole having a mass fraction of 0.983 was provided by Wuhan Senwayer Century Chemical Co., Ltd. It was recrystallized three times in methanol. The recrystallized sample had a purity of 0.995 in mass fraction, which was determined by high-performance liquid phase chromatograph (HPLC, Agilent-1260). All the solvents (ethanol, isopropanol, n-propanol, 1-butanol, methanol, ethyl acetate, toluene, acetone, acetonitrile) purchased from Sinopharm Chemical Reagent Co., Ltd., China

Melting properties measurement

With the purpose of correlating the solubility data with thermodynamic models, the melting enthalpy of 3,5-dimethylpyrazole was determined by using a differential scanning calorimetric instrument(Pyris-Diamond, PerkinElmer) under a nitrogen atmosphere. The DSC instrument was pre-calibrated with indium as the reference material in advance. About 2 mg of 3,5-dimethylpyrazole was introduced in a DSC pan, and then it was heated with a heating rate of 5 K·min⁻¹. The DSC scan of 3,5-dimethylpyrazole is

Conclusions

In this work, the equilibrium solubility were obtained experimentally for 3,5-dimethylpyrazole in a total of nine pure organic solvents within the temperature range from (283.15 to 313.15) K under 101.3 kPa. The solubility of 3,5-dimethylpyrazole in the selected pure solvents increased with the increase in temperature. At a given temperature, they ranked as 1-butanol > n-propanol > (ethanol, isopropanol, methanol, ethyl acetate, acetone) > toluene > acetonitrile. The experimental solubility data were

Acknowledgments

The authors would like to express the gratitude for the Yangzhou City Science and Technology Bureau, China, for their support (Project number: YZ2016247).

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Solubility determination and thermodynamic modelling of 3,5-dimethylpyrazole in nine organic solvents from T = (283.15 to 313.15) K and mixing properties of solutions

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Solid-liquid phase equilibrium models

Materials and apparatus

Melting properties measurement

Conclusions

Acknowledgments

Bioorg. Medicinal Chem.

ChemInform

J. Chem. Thermodynamics.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Organomet. Chem.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Synthetic modelling of the active site of native metalloenzymes by trimethylacetatozinccomplexes

Russ. J. Inorg. Chem.

Copper(II) trimethylacetate complexes with 3,5-dimethylpyrazole

Russ. J. Inorg. Chem.

Russ. J. Inorg. Chem.

Synthesis and structure of electron-deficient trimethylacetatocobalt(II) 3,5-dimethylpyrazole complexes, which are structural analogs of the active site of metalloenzymes

Russ. J. Inorg. Chem.

3,5-Dimethylpyrazole as a reagent for the gravimetric determination of cobalt

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Effect of a new hypoglycemic agent 3,5dimethylpyrazole, on carbohydrate and free fatty acid metabolism

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