Journal of Applied ChemistryVolume 2014 (2014), Article ID 450294, 7 pageshttp://dx.doi.org/10.1155/2014/450294

Research Article

Measurement and Correlation for Solubility of Some Pyrimidine Derivatives in Different Solvents

Kapil Bhesaniya and Shipra Baluja

Physical Chemistry Laboratory, Department of Chemistry, Saurashtra University, Rajkot, Gujarat 360005, India

Received 15 August 2013; Accepted 9 December 2013; Published 3 March 2014

Academic Editor: Zhen Zhao

Copyright © 2014 Kapil Bhesaniya and Shipra Baluja. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Some new pyrimidine derivatives have been synthesized and their characterization was done by IR, NMR, and mass spectral data. The solubility of these synthesized compounds has been studied in methanol, N,N dimethylformamide (DMF), and carbon tetrachloride (CCl₄) by gravimetrical method from 298.15 to 328.15 K under atmospheric pressure and the solubility data were correlated against temperature. The solubility is found to increase with temperature and order of solubility is DMF > methanol > CCl₄. The experimental solubility data is correlated with the modified Apelblat equation. Some thermodynamic parameters such as dissolution enthalpy, Gibbs energy of dissolution, and entropy of mixing have also been calculated.

1. Introduction

The pyrimidine ring is an important structure in numerous natural products and bioactive compounds [1]. Further, the pyrimidine nucleus is present as a building block in materials science [2, 3]. Literature survey reveals that as pharmacologically active compounds, substituted pyrimidine scaffolds have become increasingly important with antimicrobial [4, 5], antimalarial [6], anticancer [7], and antimycotic activities [1].

So, it will be interesting to study their solubility in different solvents due to their various applications, which may help their uses in other fields also. Thus, in the present paper, solubility of some pyrimidine derivatives in methanol, DMF, and CCl₄ from 298.15 to 328.15 K has been studied at atmospheric pressure. Some thermodynamic parameters such as dissolution enthalpy, Gibbs energy of dissolution, and entropy of mixing have also been calculated.

2. Experimental

2.1. Materials

The choice of solvent depends upon solubility and relative permeability. 2,4-Dichloropyrimidine (DCP) (CAS no.: 3934-20-1) and 4-((1H-1,2,4-triazol-1-yl)methyl)aniline (TMA) (CAS no.: 119192-10-8) used in the synthesis were purchased from Sigma-Aldrich. N,N-diisopropylethylamine (DIPEA) (CAS no.: 7087-68-5), the solvents methanol, dimethylformamide (DMF), and carbon tetrachloride (CCl₄) used in the present work were of AR grade supplied by Spectrochem Pvt. Ltd. (Mumbai, India) and were purified according to the standard procedure [8]. The purity of solvents was checked by GC-MS (SHIMADZU-Model no.-QP-2010) and found to be greater than 99.0%.

2.2. Synthesis

A mixture of 2,4-dichloropyrimidine (DCP) (1.0 equi.), 4-((1H-1,2,4-triazol-1-yl)methyl)aniline (TMA), and N,N-diisopropylethylamine (DIPEA) (1.2 equi.) in n-Butanol was refluxed for 3 h. The completion of reaction was confirmed by analytical thin layer chromatography (TLC). After completion of reaction, reaction mass was cooled and the resulting solid was filtered, washed with cold water, and dried in vacuo to give crude product.

This resulting product was refluxed for 3 h with ethanolic solution of different aromatic amines (1.1 equi.) in presence of glacial acetic acid (2-3 drops). After completion of reaction, the reaction mass was cooled and the resulting solid was filtered, washed with cold ethanol, and dried in vacuo to give crude product. The obtained crude product was purified by trituration with diethyl ether and purity of all these synthesized compounds was checked by TLC (performed on aluminum coated TLC plates Gel 60 F254 (E. Merck)). The reaction scheme is given in Figure 1.

Figure 1: The reaction scheme of pyrimidine derivatives.

2.3. Spectroscopy Study

Spectroscopic study of all the synthesized compounds was done by IR, ¹H NMR, and mass spectroscopy. IR spectra were recorded on KBr discs, using FT-IR (Shimadzu Spectrophotometer Model no.-8400). ¹H-NMR spectra were taken on a Bruker AVANCE II 400. In all the cases, NMR spectra were obtained in DMSO-d₆ using TMS as an internal standard. The NMR signals are reported in ppm. Mass spectra were determined using direct inlet probe on a GCMS-QP-2010 mass spectrometer. Melting points of compounds were measured by Differential Scanning Calorimeter (Shimadzu-DSC-60).

2.4. Solubility Measurements

The solubility was measured by a gravimetric method [9]. For each measurement, an excess mole of compound was added to a known mole of solvent. Then, the equilibrium cell was heated to a constant temperature with continuous stirring. After at least 3 h (the temperature of the water bath approached constant value, and then the actual value of the temperature was recorded), the stirring was stopped and the solution was kept still for 2 h. A portion of this solution was filtered and by a preheated injector, 2 mL of this clear solution was taken in another weighed measuring vial (). The vial was quickly and tightly closed and weighed () to determine the mole of the sample (). Then, the vial was covered with a piece of filter paper to prevent dust contamination. After the solvent in the vial had completely evaporated at room temperature, the vial was dried and reweighed () to determine the mole of the constant residue solid (). All the moles were taken using an electronic balance (Mettler Toledo AB204-S, Switzerland) with an uncertainty of ±0.0001 g. Thus, the concentration of the solid sample in the solution, mole fraction , could be determined from where is the molar mole of compound and is the molar mole of the solvent.

At each temperature, the measurement was repeated three times and an average value is given in Table 3.

3. Results and Discussion

The physical properties of all the synthesized compounds are given in Table 1. For compound BKD-5, IR and ¹H NMR spectra are shown in Figures 2 and 3, respectively.

Table 1: Physical properties of synthesized pyrimidine derivatives.

Sr. no.
Code
R
M.F
M.P.

1
BKD-1
4-Cl
C₁₉H₁₆ClN₇
130.31

2
BKD-2
4-CH₃
C₂₀H₁₉N₇
160.64

3
BKD-3
4-F
C₁₉H₁₆FN₇
197.35

4
BKD-4
3-CF₃
C₂₀H₁₆F₃N₇
205.87

5
BKD-5
3-Cl, 4-F
C₁₉H₁₅ClFN₇
225.82

Figure 2: IR spectrum of compound BKD-5.

Figure 3: ¹H NMR spectrum of compound BKD-5.

3.1. IR Spectra

The IR spectrum of BKD-5 is depicted in Figure 2. The IR data of BKD-5 clearly shows a –NH (secondary) stretching band at 3396 and 3196 cm⁻¹. The IR stretching bands at 3090–2987 cm⁻¹ and 1651–1494 cm⁻¹ confirmed the presence of aromatic C–H and C=C in basic skeleton. The absorption band at 758 cm⁻¹ and 1062–972 indicates presence of C–Cl and C–F stretching present in synthesized compounds and IR stretching band at 1379 cm⁻¹ indicates presence of triazole ring in synthesized compound. The bending vibration –CH₂ was observed at 1462 cm⁻¹, respectively. The C–H symmetric stretching and asymmetric stretching absorption are observed at 2833 cm⁻¹ and 2850 cm⁻¹, respectively. All the IR group frequencies were suggestive of the fact that pyrimidine derivative is prepared successfully.

3.2. ¹H-NMR Spectra

The proton NMR spectrum of BKD-5 is depicted in Figure 3. The peak due to residual DMSO was observed at about 3.505 ppm. It can be seen from the chemical structure of compound BKD-5 that proton of the phenyl ring attached to the carbons appeared as an appropriate multiplicity in the aromatic region at 6.463–8.698 ppm. The protons, which were present in methylene (–CH₂) (attached to phenyl ring and triazole ring), appeared as a singlet at 5.421 ppm. The other two characteristic –NH groups appeared as a singlet at 10.527 ppm and 10.8 ppm.

3.3. Solubility Measurements

The solubility of the compounds in methanol, DMF, and CCl₄ is summarized in Table 3 at temperatures ranging from 298.15 to 328.15 K. It is observed that for all the compounds, solubility is found to increase with temperature and order of solubility is DMF > methanol > CCl₄. These solubility results are correlated with the dielectric constant and dipole moment of solvents which are given in Table 2. It is observed from Table 2 that both dielectric constant and dipole moment are higher for DMF and lower for CCl₄. This is in accordance with the solubility trend in the three solvents. Thus, in present study, these properties affect the solubility. The variation of solubility in studied solvent with temperature is also shown in Figure 4.

Table 2: Dielectric constant and dipole moment of solvents.

Sr. no.
Solvent
Dielectric constant
Dipole moment

1
Methanol
32.70
1.7

2
DMF
36.71
3.86

3
CCl₄
2.238
0

Table 3: Observed mole fraction solubilities , calculated mole fraction solubilities , and relative deviation (RD) of pyrimidine derivatives in studied solvents.

/K

100 RD

100 RD

Methanol
DMF

BKD-1

298.15
0.7424
0.7032
5.2714
1.2858
1.3644

308.15
0.9546
0.9179
3.8396
2.1772
2.2143

318.15
1.2917
1.2125
6.1314
3.1280
3.3990

328.15
1.6961
1.6178
4.6146
4.7797
4.9642

BKD-2

298.15
7.2089
7.2173

6.4013
6.6624

308.15
7.5441
7.5349

9.1663
9.6171

318.15
7.8357
7.8549

12.4275
12.8846

328.15
8.1781
8.1773

15.4508
16.1567

BKD-3

298.15
1.8396
1.8414

2.9352
3.0049

308.15
2.0265
2.0266

4.5676
4.7638

318.15
2.2303
2.2336

6.8753
6.9688

328.15
2.4631
2.4642

9.1798
9.4912

BKD-4

298.15
2.1697
2.1656
0.1879
4.7890
4.8779

308.15
2.4994
2.5239
−0.9774
6.6104
6.8106

318.15
2.9719
2.9472
0.8294
8.8903
9.0000

328.15
3.4326
3.4465
−0.4054
11.0513
11.3250

BKD-5

298.15
1.8804
1.9788
−5.2320
4.3717
4.3519

308.15
2.0425
2.1480
−5.1682
7.1020
7.3718

318.15
2.1859
2.3010
−5.2636
11.9189
11.5947

328.15
2.3156
2.4359
−5.1961
16.7816
17.0697

/K

100 RD

100 RD

CCl₄

BKD-1
BKD-2

298.15
0.2086
0.2063
1.0639
0.3117
0.3199

308.15
0.5074
0.5129

0.6170
0.7129

318.15
1.0532
1.0611

1.3231
1.4269

328.15
1.8654
1.8655

2.6507
2.5944
2.1236

BKD-3
BKD-4

298.15
0.4526
0.4792

0.7293
0.7230
0.8634

308.15
0.7606
0.7935

1.0161
1.0104
0.5649

318.15
1.1252
1.2016

1.4272
1.4121
1.0633

328.15
1.5984
1.6805

1.9872
1.9724
0.7442

BKD-5

298.15
0.5563
0.5807

308.15
0.7813
0.8526

318.15
1.0849
1.2004

328.15
1.5232
1.6278

(a)

(b)

(c)

Figure 4: Variation of mole fraction solubilities () with temperature for pyrimidine derivatives, (a) in methanol, (b) in DMF, and (c) in CCl₄. BKD-1 (◊), BKD-2 (Δ), BKD-3 (+), BKD-4 (○), and BKD-5 (□). Dotted lines: .

The temperature dependence of solubility of compounds in solvents is described by the modified Apelblat equation [10, 11]. Consider where is the mole fraction solubility of compound, is the absolute temperature, and , , and are constants determined by least square analysis and values of these constants are given in Table 4. The calculated solubilities are also reported in Table 3. The experimental solubility () of synthesized compounds in the studied solvents was compared with calculated solubility () and relative deviations (RD) between the experimental and calculated value are calculated by the following equation: and the values are given in Table 3.

Table 4: Constants , , and of (2), ARD and RMSD of pyrimidine derivatives in studied solvents.

Parameters
BKD-1
BKD-2
BKD-3
BKD-4
BKD-5

Methanol

−188.055
−11.7269
−52.2145
−77.6811
49.6358

6084.210
−29.1148
1325.46
2035.83
−3161.55

28.150
1.2097
7.2786
11.3586
−7.9434

10⁵ RMSD
3.5676
0.6605
0.1126
1.0857
6.3598

100 ARD
4.964265
−0.05721
−0.07432
−0.09137
−5.21496

DMF

174.3
345.3
346.99
229.015
280.85

−11941.99
−18676.27
−19519.51
−13181.27
−17033.54

−24.72
−50.49
−50.43
−33.37
−40.22

10⁵ RMSD
9.7924
28.56
11.145
10.602
14.764

100 ARD
−5.08489
−4.31126
−2.85585
−2.1483
−0.58617

CCl₄

850.32
392.96
387.99
−136.24
121.48

−45868.6
−24351.6
−21792.9
3214.51
−8815.27

−123.73
−56.047
−56.61
20.75
−17.44

10⁵ RMSD
0.2844
4.3974
3.4608
0.6593
4.9956

100 ARD
−0.19255
−5.97058
−5.53503
0.808956
−7.75314

The relative average deviations (ARD) and root-mean-square deviations (RMSD) calculated by (4) are listed in Table 4. Consider where is the number of experimental points and is the solubility calculated by (2).

According to the Krug et al. [12] approach, the following modified Van’t Hoff expression was used to determine the enthalpy of solution (): where is the apparent standard enthalpy energy charge for the solution process and is the harmonic mean of the experimental temperatures, which is evaluated by the following equation: where is the number of experimental temperatures [13]. In the present case, the value obtained is 312.7505 K. The value of was obtained from the slope of the plot of versus () as shown in Figure 5 for methanol, DMF, and CCl₄.

(a)

(b)

(c)

Figure 5: Van’t Hoff plot for pyrimidine derivatives solubility in (a) in methanol, (b) in DMF, and (c) in CCl₄. BKD-1 (◊), BKD-2 (□), BKD-3 (Δ), BKD-4 (○), and BKD-5 (+).

The apparent standard Gibbs energy change for the solution process (), considering the approach proposed by Krug et al., is calculated at by the following equation: in which the intercept was from the plot of versus ().

Finally, using these evaluated and values, the entropies of solutions were obtained from equation [12, 14] All these thermodynamic parameters are given in Table 5.

Table 5: Thermodynamic parameters of dissolution of pyrimidine derivatives in studied solvents.

Parameters
BKD-1
BKD-2
BKD-3
BKD-4
BKD-5

Methanol

Δsol/kJ·mol⁻¹
17.6736
12.6578
15.9965
15.3516
16.0303

Δsol/kJ·mol⁻¹
22.5891
3.3855
7.8958
12.5874
5.6410

Δsol/J·mol⁻¹·K⁻¹
15.7171

DMF

Δsol/kJ·mol⁻¹
15.5336
11.8960
13.5783
12.7332
12.2834

Δsol/kJ·mol⁻¹
35.0186
23.4372
31.2108
22.8552
37.0804

Δsol/J·mol⁻¹·K⁻¹
62.3018
36.9023
56.3787
32.3644
79.2870

CCl₄

Δsol/kJ·mol⁻¹
18.9815
18.2170
18.2716
17.4786
18.1754

Δsol/kJ·mol⁻¹
59.5282
58.3892
34.0375
27.2034
27.2283

Δsol/J·mol⁻¹·K⁻¹
129.6456
128.4480
50.4103
31.0944
28.9460

It is evident from Table 5 that for all the compounds and values are positive. Further, values are also positive for all compounds in DMF and CCl₄ whereas it is negative in methanol excepting BKD-1. When stronger bonds are broken and weaker bonds are formed, energy is consumed. So, becomes positive [12] which indicates endothermic dissolution of compounds [15]. The positive value of indicates that the dissolution process is not spontaneous [12, 15]. The positive entropy change indicates that the entropy of solubilization is unfavorable for solute in solution [15], whereas negative entropy is due to more order in solutions [16]. This depends on the functional groups present in the compound as well as on the solvent. The negative entropy in methanol may be due to the fact that there may be hydrogen bonding between solute and solvent molecules which may give more ordered structure in solution, whereas in DMF and CCl₄, due to larger structure (in comparison to methanol), the structure may be disrupted, thus giving positive entropy.

Appendix

Spectral Data

BKD-1: IR (cm ⁻¹, KBr). 3375, 3225 (–NH (sec.) str.), 3095, 3036 (Ar–H str.), 2883 (–CH₂ asym. str.), 2833 (–CH₂ sym. str.), 1654–1489 (C=C str. Phenyl nucleus), 1456 (–CH₂ bending vib.), 1371 (triazole ring str.), 1273 (C–N str.), 1242–1010 (C–H in plane bending, phenyl ring), 827 (C–H oop phenyl ring), 759 (C–Cl str.), 705–675 (C–H oop triazole ring), 626 (in plane pyrimidine ring bending), 422 (Out of plane pyrimidine ring bending). ¹H NMR (DMSO-d ₆) (ppm): 5.458 (s, 2H), 6.559–6.575 (d, 1H, ), 7.308–7.329 (d, 2H, ), 7.396–7.418 (d, 2H, ), 7.518–7.538 (d, 2H, ), 7.583–7.601 (d, 2H, ) 8.019–8.037 (d, 1H, ), 8.095 (s, 1H), 8.820 (s, 1H), 10.984 (s, 1H), 11.282 (s, 1H). MS: (m/z) = 377.

BKD-2: IR (cm ⁻¹, KBr). 3394, 3217 (–NH (sec.) str.), 3088 (Ar–H str.), 3041 (–CH₂ asym. str.), 2897 (–CH₃ sym. str.), 2837 (–CH₂ sym str.), 1647–1516 (C=C str. Phenyl nucleus), 1460 (–CH₂ bending vib.), 1352 (–CH₃ asy bending) 1274 (C–N str.), 1240–972 (C–H in plane bending, phenyl ring), 868–813 (C–H oop phenyl ring), 813 (C–Cl str.), 758 (C–H oop triazole ring). ¹H NMR (DMSO-d ₆) (ppm): 2.331 (s, 3H), 5.425 (s, 2H), 6.432–6.449 (d, 1H, ), 7.161–7.181 (d, 2H, ), 7.249–7.270 (d, 2H, ), 7.342–7.363 (d, 2H, ), 7.592–7.612 (d, 2H, ), 7.930–7.947 (d, 1H, ), 8.016 (s, 1H), 8.693 (s, 1H), 10.418 (s, 1H), 10.873 (s, 1H). MS: (m/z) = 357.

BKD-3: IR (cm ⁻¹, KBr). 3391, 3213 (–NH (sec.) str.), 3059 (Ar–H str.), 2893 (–CH₂ asym. str.), 1654–1506 (C=C str. Phenyl nucleus), 1462 (–CH₂ bending vib.), 1388 (triazole ring str), 1273 (C–N str.), 1219–1136 (C–H in plane bending, phenyl ring), 1018 (C–F str.), 835–768 (C–H oop phenyl ring), 767 (C–H oop triazole ring). ¹H NMR (DMSO-d ₆) (ppm): 5.36 (s, 2H), 6.2–6.214 (d, 1H, ), 7.114–7.212 (m, 4H), 7.22–7.247 (m, 1H), 7.605–7.627 (d, 2H, ), 7.721–7.765 (m, 1H), 7.963–7.981 (d, 2H, ), 8.635 (s, 1H), 8.699 (s, 1H), 9.432 (s, 1H). MS: (m/z) = 361.

BKD-4: IR (cm ⁻¹, KBr). 3311, 3203 (–NH (sec.) str.), 3107–3041 (Ar–H str.), 2951 (–CH₂ asym. str.), 2883 (–CH₂ sym str.), 1637–1491 (C=C str. Phenyl nucleus), 1456–1419 (–CH₂ bending vib.), 1334 (triazole ring str), 1271 (C–N str.), 1230–1157 (C–H in plane bending, phenyl ring), 1107–1014 (C–F str.), 966–848 (C–H oop phenyl ring), 794–650 (C–H oop triazole ring). ¹H NMR (DMSO-d ₆) (ppm): 5.377 (s, 2H), 6.279–6.293 (d, 1H, ), 7.222–7.257 (t, 3H, ), 7.434–7.474 (t, 1H, ), 7.686–7.707 (d, 2H, ), 7.996–8.012 (d, 2H, ), 8.068–8.083 (d, 1H, ), 8.175 (s, 1H), 8.654 (s, 1H), 9.521 (s, 2H). MS: (m/z) = 411.

BKD-5: IR (cm ⁻¹, KBr). 3396, 3196 (–NH (sec.) str.), 3090–2987 (Ar–H str.), 2850 (–CH₂ asym. str.), 2833 (–CH₂ sym str.), 1651–1494 (C=C str. Phenyl nucleus), 1462 (–CH₂ bending vib.), 1379 (triazole ring str), 1265 (C–N str.), 1205, 1139 (C–H in plane bending, phenyl ring), 1060–972 (C–F str.), 879–819 (C–H oop phenyl ring), 758 (C–Cl str.), 680–509 (C–H oop triazole ring). ¹H NMR (DMSO-d ₆) (ppm): 5.421 (s, 2H), 6.463–6.480 (d, 1H, ), 7.286–7.307 (d, 2H, ), 7.333–7.353 (d, 2H, ), 7.405–7.422 (d, 2H, ), 7.903–7.920 (d, 1H, ), 8.004–8.021 (d, 2H, ), 8.685–8.698 (d, 1H, ), 10.52 (s, 1H), 10.8 (s, 1H). MS: (m/z) = 395.

Nomenclature

: | Concentration (mol·L⁻¹)
: | Absolute temperature (K)
: | Experimental solubility ()
: | Calculated mole fraction solubility ()
: | Enthalpy of solution
: | Gibbs energies of dissolution (kJ·mol⁻¹)
: | Entropy of solutions (kJ·mol⁻¹)
: | Universal gas constant (J·mol⁻¹·K⁻¹)
: | Harmonic temperature (K).

Abbreviations

DCP: | 2,4-Dichloropyrimidine
TMA: | 4-((1H-1,2,4-Triazol-1-yl)methyl)aniline
DIPEA: | N,N-Diisopropylethylamine
DMF: | N,N-Dimethylformamide
CCl₄: | Carbon tetrachloride
AR: | Analytical reagent
AAD: | Absolute average deviations
rmsd: | Root-mean-square deviations
RD: | Relative deviations.

Conflict of Interests

The authors of this paper do not have a direct financial relation with the commercial identity that might lead to a conflict of interests for any of the authors.

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