Comment/Reply pubs.acs.org/jced
Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Comment on “Determination and Correlation of Dipyridamole p‑Toluene Sulfonate Solubility in Seven Alcohol Solvents and Three Binary Solvents” William E. Acree, Jr.* Department of Chemistry, University of North Texas, 1155 Union Circle Drive #305070, Denton, Texas 76203, United States ABSTRACT: Errors are found in the authors published equation coefficients for the modified Apelblat equation. Backcalculated mole fraction solubilities based on the published equation coefficients differ significantly from the back-calculated values that the authors reported.
I
n a recent paper published in This Journal, Li and coworkers1 reported the solubility of dipyridamole p-toluene sulfonate in seven different organic monosolvents (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, isobutyl alcohol, 2butanol) and in three different binary (methanol + ethanol, methanol +1-propanol, methanol +1-butanol) solvent mixtures. Experimental solubilities were measured by a gravimetric method at temperatures ranging from 288.15 to 328.15 K. As part of the study the authors correlated their experimental solubility data using the modified Apelblat model, the CNIBS/ R-K model, and the modified version of Jouyban−Acree models (the Combined Apelblat and Jouyban−Acree equation). 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 manuscript. The calculated equation coefficients have either been miscalculated, or rounded to the point where the coefficients fail to backcalculate the observed mole fraction solubility data. The purpose for deriving mathematical representations that describe how the measured solubility varies with temperature and/or solvent composition is two-fold. First, the mathematical representation provides a convenient means to check the measured values for possible outliers. Large deviations between an experimental data point and the back-calculated value would indicate an experimental value in possible need of redetermination. Second, the mathematical representation would enable journal readers to estimate values at temperatures and solvent compositions not studied by the authors. Journal readers expect that the published mathematical correlation will describe the observed data to within the deviations given by the authors. Let us now examine the back-calculated mole fraction solubilities, x1, based on the modified Apelblat model, ln x1 = A +
B + C ln T T
ln x1 = −233 +
(2)
ln x1 = −233 + 25.457 + 201.125
(3)
ln x1 = −6.418
(4)
I calculate a mole fraction solubility of x1 = 0.001632, which differs significantly from the back-calculated value of x1 = 0.002245 that the authors give in the third column of Table 2 for the mole fraction solubility of dipyridamole p-toluene sulfonate in methanol at T = 298.15 K. Next I calculate the solubility of dipyridamole p-toluene sulfonate in 1-butanol at T = 298.15 K by substituting the authors calculated equation coefficients (10−2A = −0.26; 10−3B = −2.09; 10−1C = 0.44) from Table S1 into eq 1 above to give: ln x1 = −26 −
2090 + 4.4 ln 298.15 298.15
(5)
ln x1 = −26 − 7.010 + 25.069
(6)
ln x1 = −7.941
(7)
I calculate a mole fraction solubility of x1 = 0.000356, which is approximately 18.6 relative percent larger than the backcalculated value of x1 = 0.000300 that the authors gave in Table 2 for the solubility of dipyridamole p-toluene sulfonate in 1butanol at T = 298.15 K. Similarly I calculate the solubility of dipyridamole p-toluene sulfonate in 2-butanol at T = 298.15 K by substituting the authors calculated equation coefficients (10−2A = 2.49; 10−3B = −15.08; 10−1C = −3.64) from Table S1 into eq 1 above: ln x1 = 249 −
(1)
15080 − 36.4 ln 298.15 298.15
ln x1 = 249 − 50.579 − 207.393
using the authors’ calculated equation coefficients (A, B, and C). Specifically I calculate the mole fraction solubility of dipyridamole p-toluene sulfonate in methanol at T = 298.15 K by substituting the authors’ calculated equation coefficients (10−2A = −2.33; 10−3B = 7.59; 10−1C = 3.53) from Table S1 into eq 1 above to give: © XXXX American Chemical Society
7590 + 35.3 ln 298.15 298.15
ln x1 = −8.972
(8) (9) (10)
Received: January 12, 2018 Accepted: April 24, 2018
A
DOI: 10.1021/acs.jced.8b00042 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Comment/Reply
to give a calculated mole fraction solubility of x1 = 0.000127. The back-calculated value that the authors reported in Table 2, x1 = 0.000191, is approximately 50% larger. Unfortunately, the problem is not confined to the modified Apelblat equation coefficients for the monosolvents. I now calculate the mole fraction solubility of dipyridamole p-toluene sulfonate in the binary (methanol + ethanol) solvent mixture at T = 298.15 and at an initial binary solvent composition of xMeOH = 0.10 by substituting the equation coefficients (10−2A = 0.19; 10−3B = −3.86; 10−1C = −0.22) from Table S2 into eq 1 above: ln x1 = 19 −
3860 − 2.2 ln 298.15 298.15
(11)
ln x1 = 19 − 12.947 − 12.535
(12)
ln x1 = −6.482
(13)
I calculate a mole fraction solubility of x1 = 0.00153, which is approximately 86% larger than the back-calculated value of x1 = 0.000823 that the authors gave in Table 3 for the solubility of dipyridamole p-toluene sulfonate in this particular binary solvent mixture at T = 298.15 K. Mathematical correlations are meaningless whenever the reported curve-fit equation coefficients do not properly backcalculate the observed solubility data. In the case of the published paper of Li and co-workers1 journal readers must recalculate the equation coefficients in order to use the modified Apelblat model to make solubility predictions at other temperatures. Authors that report mathematical representations need to carefully check the equation coefficients that they report to ensure that the numerical values correctly backcalculate the observed data. This should be done prior to the manuscript being submitted for publication. Reviewers should not be expected to check every one of the authors’ calculations, and journal readers should not have to recalculate the authors’ published equation coefficients in order to make predictions at other temperatures and/or solvent compositions.
■
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.
■
REFERENCES
(1) Li, M.; Liu, S.; Li, S.; Yang, Y.; Cui, Y.; Gong, J. Determination and correlation of dipyridamole p-toluene sulfonate solubility in seven alcohol solvents and three binary solvents. J. Chem. Eng. Data 2018, 63, 208−216.
B
DOI: 10.1021/acs.jced.8b00042 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
