Comment/Reply pubs.acs.org/jced
Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Comment on “Solution Thermodynamics of Benzotriazole in Different Pure Solvents” William E. Acree, Jr.* Department of Chemistry, University of North Texas, 1155 Union Circle Drive #305070, Denton, Texas 76203, United States ABSTRACT: Mole fraction solubilities were calculated for benzotriazole dissolved in methanol, 2-propanol, 2-butanol, and acetonitrile at 298.15 K based on the published equation coefficients for the modified Apelblat model. In the case of the three alcohol solvents, the calculated mole fraction solubilities of benzotriazole were found to differ by up to 30% from the backcalculated values that the authors reported in their published paper. A significantly larger difference was found in the case of benzotriazole dissolved in acetonitrile.
I
n a recent paper published in the Journal of Chemical and Engineering Data Luan and co-workers1 reported the solubility of benzotriazole in 14 different organic solvents. Solubilities were determined in the temperature range from 268.15 to 303.15 K using a static gravimetric method of analyses. Excess benzotriazole and solvent were allowed to equilibrate at constant temperature in a jacketed glass vessel. After attainment of equilibrium, a 2 mL aliquot of the supernatant was removed and transferred into a preweighed glass vial through an organic membrane. The vial and contents were immediately weighed and then placed into a vacuum drying oven at 323.15 K in order to remove the organic solvent. Once the solvent had evaporated, the mass of the vial plus solid residue was determined. The mole fraction solubility was then calculated from the mass of the solid residue, the mass of the supernatant aliquot taken for analysis, and the molar masses of benzotriazole and the respective organic solvent. As part of the study, the authors correlated the variation in the mole fraction solubility with temperature in terms of the modified Apelblat equation, Buchowski−Ksiazczak (λh) equation, the Wilson equation, and the Nonrandom two-liquid model (NRTL). In the present commentary, I will show that the authors’ published modified Apelblat equations do not describe the experimental solubility as stated in the published article. The calculated equation coefficients have either been miscalculated or rounded to the point where the coefficients fail to give the authors’ backcalculated mole fraction solubilities. Let us now examine the back-calculated mole fraction solubilities, x1, based on the modified Apelblat model: ln x1 = A + (B /T ) + C ln T
I calculate a value of x1 = 0.3166 for the mole fraction solubility of benzotriazole in methanol at T = 298.15 K, which is approximately 18% smaller than the back-calculated value of x1 = 0.3888 that the authors give in the third column of Table 3 in their published paper.1 Next I calculate the solubility of benzotriazole in 2-propanol at T = 298.15 K by substituting the authors calculated equation coefficients (A = −67.30; B = 1825; C = 10.60) from Table S1 into eq 1 above to give:
ln x1 = −96.20 + 10.156 + 84.894
(3)
ln x1 = −1.150
(4) © XXXX American Chemical Society
ln x1 = −67.30 + 6.121 + 60.395
(6)
ln x1 = −0.784
(7)
ln x1 = −115.0 + (4004/298.15) + 17.70 ln 298.15
(8)
ln x1 = −115.0 + 13.429 + 100.848
(9)
ln x1 = −0.723
(10)
The mole fraction solubility that I back-calculate using the authors’ tabulated curve-fit equation coefficients, x1 = 0.4853, is approximately 28.6% larger than the value of x1 = 0.3772 that the authors give in Table 3 of their published paper1 for the solubility of benzotriazole dissolved in 2-butanol at 298.15 K. Finally, I calculate the solubility of benzotriazole in acetonitrile at T = 298.15 K by substituting the authors’
using the authors’ calculated equation coefficients (A, B, and C). Specifically, I calculate the mole fraction solubility of benzotriazole in methanol at T = 298.15 K by substituting the authors’ curve-fit equation coefficients (A = −96.20; B = 3028; C = 14.90) from Table S1 of the Supporting Information into eq 1 above: (2)
(5)
I calculate a mole fraction solubility of x1 = 0.4566 for benzotriazole dissolved in 2-propanol at 298.15 K. The authors’ back-calculated value of x1 = 0.3715 from Table 3 is approximately 18% smaller than the value that I calculated with the authors’ curve-fit equation coefficients. Similarly, I calculate the solubility of benzotriazole in 2butanol at T = 298.15 K by substituting the authors’ calculated equation coefficients (A = −115.0; B = 4004; C = 17.70) from Table S1 into eq 1 above:
(1)
ln x1 = −96.20 + (3028/298.15) + 14.90 ln 298.15
ln x1 = −67.30 + (1825/298.15) + 10.60 ln 298.15
Received: March 10, 2018 Accepted: April 17, 2018
A
DOI: 10.1021/acs.jced.8b00190 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Comment/Reply
calculated equation coefficients (A = −167.0; B = 484.6; C = 2.630) from Table S1 into eq 1 above: ln x1 = −167.0 + (484.6/298.15) + 2.630 ln 298.15 (11)
ln x1 = −167.0 + 1.625 + 5.698
(12)
ln x1 = −159.68
(13)
The mole fraction solubility that I back-calculate using the authors’ tabulated curve-fit equation coefficients, x1 = 4.49 × 10−70, is nowhere close to the value of x1 = 0.09686 that the authors give in Table 3 of their published paper1 for the solubility of benzotriazole in acetonitrile. The only way that I can come close to the authors’ back-calculated value is to assume that both the B and C were off by a factor of ten. Using B = 4846 and C = 26.30, I calculate mole fraction solubility of x1 = 0.4067, which is still considerably different from the authors’ back-calculated value of x1 = 0.09686 in Table 3 of their published paper.1 The calculations that I spot checked, as documented above, clearly show that the curve-fit equation coefficients that Luan and co-workers reported in their published paper1 for the modified Apelblat equation coefficients fail to describe the solubility behavior of benzotriazole in four of the organic solvents. I did not perform calculations for all 14 of the organic solvents studied by the authors. Readers should exercise caution in using the values to make solubility predictions at other temperatures.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: 940-565-4318. ORCID
William E. Acree Jr.: 0000-0002-1177-7419 Notes
The author declares no competing financial interest.
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REFERENCES
(1) Luan, Y.; Li, J.; Kaliwanda, M.; Wang, N.; Chen, K.; Li, X.; Su, W.; Hao, H. Solution thermodynamics of benzotriazole in different pure solvents. J. Chem. Eng. Data 2018, DOI: 10.1021/acs.jced.7b01085.
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DOI: 10.1021/acs.jced.8b00190 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
