www.bacpl.org/j/pcc PHYSICAL CHEMISTRY COMMUNICATIONS Volume 1 Issue 1, October 2014
Dissolution Enthalpy and Entropy of Thiourea in Triglycol Solution Wanren Chen1, Hua Li1*, Xiaoshuang Chen2 School of Chemical and Energy Engineering, Zhengzhou University, Zhengzhou, China, 450001 School of Energy and Power Engineering, Xiʹan Jiaotong University, Xiʹan, Shaanxi, China, 710049
1 2
wrchen@zzu.edu.cn; lihua@zzu.edu.cn; 653852518@qq.com Received 3 October 2013; Revised 29 January 2014; Accepted 13 February 2014; Published 17 October 2014 © 2014 BIOLOGICAL AND CHEMICAL PUBLISHING Abstract The solubility of thiourea in triglycol + water mixture has been determined with the mass fraction of triglycol (ω) being 0.63, 0.72, 0.82, and 0.91. The experimental data have been correlated with the modified Apelblat equation. The dissolution enthalpy and dissolution entropy have been calculated from the experimental data. The mutual interactions between solvent and solute have been discussed in brief. Key words: Solubility; Dissolution Enthalpy; Dissolution Entropy; Thiourea; Triglycol Solution
Introduction Thiourea is a very important pharmaceutical intermediate and chemical material, which is widely used in synthetizing sulfnamides, dyestuff, resin and other substances. During the producing process, it’s significant to obtain the solubility and thermodynamic properties of thiourea in triglycol + water solution. In the literature [1], the solubility of thiourea in triglycol + water had been determined from 292.05 to 357.75 K by the synthetic method. Based on the solubilities of thiourea in triglycol + water mixtures with the mass fraction of triglycol being 0.63, 0.72, 0.82 and 0.91 [2], the solubility data were correlated by the modified Apelblat equation and the dissolution enthalpy and dissolution entropy had been calculated, and the solubilities correlated by the modified Apelblat equation showed good agreement with the experimental data. Experimental Section Materials Thiourea, triglycol, and water were of analytical grade, and all obtained from Shanghai Chemical Reagent Co. and had the mass fraction purities of 0.995. Deionized water was used. Solubility Measurement The solubilities of thiourea in triglycol + water were measured by a synthetic method at atmospheric pressure which can be seen in the previous article [2]. The solubility of thiourea expressed by the mole fraction is shown as follows [3]. x
m1 / M 1 (1) m1 / M 1 m2 / M 2 m3 / M 3
Where m1 represents the mass of solute, m2 and m3 represent the mass of solvents, respectively. M1 is the molecular weight of solute and M2, M3 are the molecular weights of solvents, respectively. 1= thiourea, 2= triglycol, 3=water Test of Apparatus To prove the feasibility and the uncertainty of the measurement, the solubility of NaCl in water was measured and
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compared with the values reported in the literature [4]. The experimental data agreed with the reported values with a mean relative deviation of 0.18 % and 2.5 %, respectively. The measured values are listed in Table 1. TABLE 1 SOLUBILITY OF NACL IN 100g WATER
T/K x x[4] 100 RD 293.15 0.0996 0.0998 ‐0.20 313.15 0.1015 0.1013 0.20 333.15 0.1033 0.1030 0.29 353.15 0.1061 0.1058 0.28 373.15 0.1090 0.1092 ‐0.18
Result and Discussion The measured solubilities of thiourea in triglycol+ water solution at different temperatures can be seen in the Table 2. TABLE 2 MOLE FRACTION SOLUBILITIES OF THIOUREA IN TRIGLYCOL + WATER MIXTURES
T/K x xc 102RD T/K x xc 102RD ω=0.63 303.45
0.1449
0.1423
‐1.79
322.75
0.1883
0.1903
307.65
0.1515
0.1542
‐1.78
326.05
0.2002
0.1999
‐1.06 0.15
312.15
0.1605
0.1660
‐3.43
329.55
0.2086
0.2113
‐1.29
315.85
0.1675
0.1734
‐3.52
334.25
0.2229
0.2286
‐2.56
318.75
0.1780
0.1800
‐1.12
338.45
0.2322
0.2365
‐1.85
293.15
0.1686
0.1705
‐1.13
318.85
0.2316
0.2266
2.16
296.15
0.1792
0.1837
‐2.51
321.15
0.2387
0.2331
2.35
300.25
0.1885
0.1888
‐0.16
323.75
0.2435
0.2409
1.07
304.65
0.1989
0.1957
1.61
327.25
0.2547
0.2524
0.90
309.25
0.2057
0.2041
0.78
330.15
0.2621
0.2628
‐0.27
313.65
0.217
0.2136
1.7
332.85
0.2682
0.2733
‐1.90
316.45
0.2244
0.2203
1.83
335.95
0.2744
0.2863
‐4.34
ω=0.72
ω=0.82 292.05
0.2222
0.2315
‐4.18
320.35
0.2824
0.2782
1.48
292.25
0.2226
0.2317
‐4.09
321.65
0.2851
0.2811
1.4
292.85
0.2232
0.2324
‐4.12
324.35
0.2924
0.2873
1.74
297.25
0.2344
0.2378
‐1.45
327.55
0.2987
0.2951
1.21
301.35
0.2399
0.2435
‐1.5
331.15
0.3044
0.3044
0
301.55
0.2459
0.2438
0.85
332.85
0.3085
0.309
‐0.16
305.75
0.2527
0.2503
0.95
336.65
0.3173
0.3198
‐0.79
305.95
0.2552
0.2507
1.76
339.95
0.3254
0.3297
‐1.32
310.55
0.2651
0.2586
2.45
342.55
0.3330
0.3379
‐1.47
311.65
0.2642
0.2606
1.36
345.65
0.3414
0.3481
‐1.96
314.85
0.2726
0.267
2.05
348.65
0.3525
0.3585
‐1.7
319.15
0.2774
0.2756
0.65
ω=0.91
309.75
0.3248
0.3367
‐3.66
336.05
0.3714
0.3748
‐0.92
311.25
0.3313
0.3381
‐2.05
339.05
0.3778
0.381
‐0.85
313.15
0.3345
0.3399
‐1.61
342.25
0.3843
0.388
‐0.96
315.95
0.3372
0.343
‐1.72
345.65
0.3910
0.396
‐1.28
319.35
0.3418
0.3472
‐1.58
348.15
0.3947
0.4022
‐1.9
321.55
0.3472
0.3502
‐0.86
351.75
0.4045
0.4117
‐1.78
324.85
0.3497
0.355
‐1.52
354.35
0.4098
0.4188
‐2.2
327.85
0.3547
0.3598
‐1.44
357.75
0.4166
0.4287
‐2.9
332.05
0.3637
0.3671
‐0.93
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www.bacpl.org/j/pcc PHYSICAL CHEMISTRY COMMUNICATIONS Volume 1 Issue 1, October 2014
The temperature dependence of thiourea in triglycol + water mixtures is described by the modified Apelblat equation [5, 6]. ln x A
B C ln T T
(2)
Where x is the mole fraction solubility of thiourea, T is the absolute temperature, and A, B, C are the model parameters, which can be obtained from optimization and fitting. The values are listed in Table 3. TABLE 3 PARAMETERS OF EQUATION 2 FOR THIOUREA IN TRIGLYCOL + WATER MIXTURES
ω A B C R2 103RMSD 102RAD 0.63 ‐255.33 10798.39 38.12 0.983 3.807 2.882 0.72 ‐196.62 8161.00 29.41 0.971 3.604 2.035 0.82 ‐92.98 3648.85 13.92 0.982 2.227 1.401 0.91 ‐89.99 3872.20 13.32 0.992 3.848 1.657
The root‐mean‐square‐deviation (RMSD), relative deviation (RD), and relative average deviation (RAD) are calculated respectively according to the previous reference [2]. The model parameters, RAD, and RMSD are listed in Table 3. The relative deviations between experimental values and calculated values are listed in Table 2. From Table 2, it can be seen that the experimental data show good agreement with the calculated data. And the relative average deviations of thiourea in triglycol + water mixtures are 2.882%, 2.035%, 1.401%, and 1.657% respectively, which indicates that the Apelblat equation is fit to correlate the solubility data of thiourea in triglycol + water mixtures. Thermodynamic functions related with solubility are mainly dissolution enthalpy and dissolution entropy, namely ΔH and ΔS, which can be obtained though a series of equations. According to a pseudochemical reaction process [7], the dissolution process of solid S in liquid W, can be expressed as S+W=SW; the relationship between its dissolution equilibrium and activities can be expressed as: Ki
ai (3) as aw
Where ai stands for the activity of thiourea in the solution, as and aw represent the activities of pure solid S and pure liquid W, respectively. Because of the relatively small solubility of thiourea in solvent, it is believed that a s and a w almost remains constant in the experimental range, and each is considered to be a constant. Meanwhile, the activity ai and the mole fraction xi are related by the Equation (4), which is shown below. Therefore Equation (3) can be written as Equation (5) as below. ai i xi (4) Ki
i xi (5) as aw
Where γi is the activity coefficient of thiourea, and xi is the mole fraction of thiourea in the solution. By logarithmic treatment, Equation (5) can be changed into: ln Ki ln xi J (6)
Where J=lnγi‐ln (as *aw), which is a constant independent off temperature. On the basis of Gibbs equation and the modified Van’t Hoff method [8], the equation for calculating molar enthalpies of dissolution ΔsolH can be obtained: sol H R
d ln K i dT 1
(7)
That is to say,
sol H R
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d ln xi dT 1 (8)
PHYSICAL CHEMISTRY COMMUNICATIONS Volume 1 Issue 1, October 2014 www.bacpl.org/j/pcc
Then Equation (2) is used to obtain the derivation and then substituted into Equation (8), thus Equation (9) is given below. sol H R T (C
B ) (9) T
According to the fundamental thermodynamic relation [9], the equation for calculating the molar entropy of dissolution ΔsolS can be obtained accordingly: sol S R (C
B ) (10) T
R is the molar gas constant, whose value is 8.314 J∙mol‐1∙K‐1; According to the parameters of modified Apelblat equation listed in Table 3, ΔsolH and ΔsolS can be calculated by Equation (9) and Equation (10), which is listed in Table 4. TABLE 4 ΔSOLH (KJ MOL‐1) AND ΔSOLS (J MOL‐1 K‐1) FOR THIOUREA IN TRIGLYCOL SOLVENT WITH THE MASS FRACTION OF THIOUREA BEING 0.63, 0.72. 0.82,
0.91 AND 1.00 RESPECTIVELY T/K
ΔsolH (kJ mol‐1)
ΔsolS (J mol‐1 K‐1)
T/K
ΔsolH (kJ mol‐1)
ΔsolS (J mol‐1 K‐1)
303.45
6.394
21.073
307.65
322.75
12.511
38.764
7.726
25.112
326.05
13.557
41.580
312.15
9.152
29.319
329.55
14.666
44.504
315.85
10.324
32.688
334.25
16.156
48.335
318.75
11.243
35.274
338.45
17.487
51.668
ω=0.63
ω=0.72 293.15
3.829
13.061
318.85
10.113
31.717
296.15
4.562
15.405
321.15
10.675
33.241
300.25
5.565
18.534
323.75
11.311
34.938
304.65
6.641
21.798
327.25
12.167
37.179
309.25
7.766
25.111
330.15
12.876
39.000
313.65
8.841
28.189
332.85
13.536
40.667
316.45
9.526
30.103
335.95
14.294
42.548
ω=0.82 292.05
3.463
11.856
320.35
6.738
21.033
292.25
3.486
11.927
321.65
6.888
21.416
292.85
3.555
12.140
324.35
7.201
22.201
297.25
4.064
13.674
327.55
7.571
23.114
301.35
4.539
15.062
331.15
7.988
24.121
301.55
4.562
15.129
332.85
8.184
24.589
305.75
5.048
16.511
336.65
8.624
25.618
305.95
5.071
16.576
339.95
9.006
26.493
310.55
5.604
18.044
342.55
9.307
27.170
311.65
5.731
18.389
345.65
9.666
27.964
314.85
6.101
19.378
348.65
10.013
28.719
319.15
6.599
20.677
ω=0.91
309.75
2.109
6.809
336.05
5.022
14.943
311.25
2.275
7.310
339.05
5.354
15.790
313.15
2.486
7.937
342.25
5.708
16.678
315.95
2.796
8.848
345.65
6.085
17.604
319.35
3.172
9.933
348.15
6.362
18.272
321.55
3.416
10.623
351.75
6.760
19.219
324.85
3.781
11.640
354.35
7.048
19.890
327.85
4.113
12.547
357.75
7.425
20.754
332.05
4.579
13.789
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It can be seen from Table 4 that at the same temperature, ΔsolH and ΔsolS both decrease when the mass fraction of triglycol (ω) increases, ΔsolH and ΔsolS increase when the temperature increases and mass fraction of triglycol (ω) keeps stable; and the process of thiourea dissolving in triglycol + water mixtures during the temperature range is endothermic, ΔsolH＞0. The endothermic effect happens mainly because the interactions between thiourea and the solvent are more powerful than those between the solvent molecules. Meanwhile, ΔsolS for the process is positive, which reveals that it is irreversible processes. Conclusion The solubilities of thiourea in triglycol solution were measured, and the experimental data were correlated with the Apelblat equation, also the dissolution enthalpies ΔsolH and dissolution entropies ΔsolS were calculated. The overall RMSD is 1.349×10‐2, indicating that the calculated data show good agreement with the experimental data. The positive ΔsolH and ΔsolS revealed the process is endothermic and entropy‐driven. The experimental solubilities and correlation equation in this work can be used as essential and basic data for the preparation of thiourea. Literature Cited [1]
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