Article pubs.acs.org/jced
Solubility and Thermodynamic Properties of (2S)‑Pyrrolidine-2carboxylic Acid in Water, Alcohols, and Water−Alcohol Mixtures Erhong Duan,*,† Kunkun Wang,† Xue Li,† Zidan Chen,† and Hua Sun*,‡ †
School of Environmental Science and Engineering, and ‡College of Chemical & Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018, People’s Republic of China ABSTRACT: The solubility of (2S)-pyrrolidine-2-carboxylic acid in pure alcohols (methanol, ethanol, isopropyl alcohol, and butan-1-ol) and the aqueous alcohols (methanol, ethanol, and isopropyl alcohol) mixtures was measured by a dynamic method via a laser monitoring technique. The solubility in the pure alcohols follows the order methanol > ethanol > butan-1ol > isopropyl alcohol. In the binary mixtures, the solubility decreases with the increase of alcohol concentration. The experimental solubility was fitted by the modified Apelblat equation, combined nearly ideal binary solvent/Redlich−Kister (CNIBS/R-K) model, and Van’t Hoff equation. The dissolution is endothermic and the dissolution driving force converts from enthalpy-driven to entropy-driven.
1. INTRODUCTION (2S)-Pyrrolidine-2-carboxylic acid (C5H9NO2, CAS No. 147-85-3, Figure 1.) is a nonessential amino acid that can be converted to
usually used as solvents for the crystallization of (2S)-pyrrolidine2-carboxylic acid from the mixture of (2S)-pyrrolidine-2carboxylic acid and (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid. It is necessary to know the solubility data in the related solvents for the purification and refining process. A review of the literature of (2S)-pyrrolidine-2-carboxylic acid, however, indicated that only some solubility data were reported.4 Held measured the solubility of (2S)-pyrrolidine-2-carboxylic acid in water at 298.15 K.5 No systematic experimental solubility data in pure solvents and aqueous−alcohols solutions were available. In this paper, the solubility data of (2S)-pyrrolidine-2carboxylic acid in pure solvents (methanol, ethanol, isopropyl alcohol, and butan-1-ol), water−methanol, water−ethanol, and water−isopropyl alcohol mixtures was measured. The experimental data of (2S)-pyrrolidine-2-carboxylic acid in pure solvents were correlated by the modified Apelblat equation and the binary mixtures were fitted by combined nearly ideal binary solvent/Redlich−Kister (CNIBS/R-K) model. The thermodynamic properties of (2S)-pyrrolidine-2-carboxylic acid in pure solvents and the solutions, including the enthalpy and entropy, were calculated by the Van’t Hoff equation.
Figure 1. Chemical structure of (2S)-pyrrolidine-2-carboxylic acid.
glutamic acid, which is incorporated into tissue proteins.1 (2S)-pyrrolidine-2-carboxylic acid is widely used as an ingredient of foods and reagents in pharmaceutical industry. (2S)Pyrrolidine-2-carboxylic acid has been used in many reactions as catalyst, such as the Mannich reactions and the direct asymmetric Aldol reactions.2 Dietary supplements containing crystalline (2S)-pyrrolidine-2-carboxylic acid are commercially available also.3 (2S)-Pyrrolidine-2-carboxylic acid is prepared usually by three methods: chemical synthesis, biological fermentation, and protein hydrolysis. Ion-exchange is used to separate the mixture of (2S)pyrrolidine-2-carboxylic acid and (2S,4R)-4-hydroxypyrrolidine2-carboxylic acid during the protein hydrolysis of celluloid, because of their similar structure and properties. Ion-exchange has some advantages, such as environment friendly and high quality productions ((2S)-pyrrolidine-2-carboxylic acid and (2S,4R)-4hydroxypyrrolidine-2-carboxylic acid). Along with these benefits, there are certain disadvantages associated with ion-exchange, such as high maintenance cost and energy consumption, low productivity, calcium sulfate fouling, and chlorine contamination, etc. The crystallization process is usually used to separate and purify amino acid also. The alcohol−water mixtures are © XXXX American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. (2S)-Pyrrolidine-2-carboxylic acid, 99.5 mass fraction was supplied by Huayang Chemical Co., Ltd., Jizhou, China. Methanol, ethanol, and butan-1-ol were supplied by Tianjin Yongda Chemical Reagent Co., Ltd., Tianjin, China. Isopropyl alcohol was supplied by Tianjin Fuyu Fine Chemical Co., Ltd., Tianjin, China. The purities of alcohols (methanol, ethanol, isopropyl alcohol, and butan-1-ol) determined by gas Received: August 26, 2014 Accepted: January 20, 2015
A
DOI: 10.1021/je5007949 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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chromatography are higher than 99.5 in mass fraction, respectively. Distilled HPLC grade deionized water was used. 2.2. Apparatus and Procedure. The solubility was measured by a laser method, which was described in previous works.6 The solubility was measured with a 100 mL jacked glass vessel at constant temperature through a thermostated bath with an uncertainty of ± 0.05 K. The dissolution of the solute was examined by a laser beam penetrating the vessel. An analytical balance (Metler Toledo AB204-N, Switzerland) with an uncertainty of ± 0.0001 g was used. The same experiments were measured at least three times. The mean values were calculated and used to get the mole fraction solubility, x1, based on eq 1. The compositions of solvent mixtures, x2, were defined in eq 2. x1 =
m1/M1 m1/M1 + ∑ mi /Mi
(1)
x2 =
m2 /M 2 m2 /M 2 + m3 /M3
(2)
Table 2. Parameters for Correlation eq 3 of (2S)Pyrrolidine-2-carboxylic Acid in Pure Alcohols (Ethanol, Butan-1-ol, and Isopropyl Alcohol) and Methanol from 298.15 K to 348.15 K and from 291.15 K to 331.15 K, Respectively solvent
A
B
C
dev. %
methanol ethanol ethanol butan-1-ol isopropyl alcohol
102.2967 −142.2994 −142.2994 173.4413 201.0374
−6488.0310 3696.4468 3696.4468 −10801.8119 −12606.1228
−14.6374 21.8538 21.8538 −25.1565 −29.1182
1.2701 1.8763 1.8763 1.2554 1.1784
where m1, m2, and m3 are the mass of the (2S)-pyrrolidine-2carboxylic acid, methanol and according solvents, respectively. M1, M2, and M3 are molecular weight of the (2S)-pyrrolidine-2carboxylic acid, methanol, and according solvents, respectively.
3. RESULTS AND DISCUSSION 3.1. Pure Solvents. The solubilities of (2S)-pyrrolidine-2carboxylic acid in methanol and ethanol, isopropyl alcohol, and butan-1-ol were measured in the temperature range from 291.15 K to 331.15 K, and 298.15 K to 348.15 K, respectively (Table 1). The solubility in alcohols follows the order methanol
Figure 2. Van’t Hoff plots of ln x1 verse 1/T in different pure organic solvents from 291.15 K to 348.15 K: ■, methanol; ●, ethanol; ▲, butan-1-ol; ▼, isopropyl alcohol. Solid line, values calculated from eq 5
Table 1. Experimental Mole Fraction Solubilities x1 of (2S)-Pyrrolidine-2-carboxylic Acid in Pure Alcohols at Temperature T and Pressure p = 0.1 MPaa solvent methanol
ethanol
butan-1-ol
isopropyl alcohol
T/K
102x1
100(x1 − xcal/x1)
291.15 301.15 311.15 321.15 331.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15
4.8897 5.9700 7.6104 9.2507 10.7051 0.4472 0.6423 0.8521 1.2314 1.6217 2.2925 0.2177 0.3200 0.4085 0.5427 0.6772 0.8078 0.0767 0.1192 0.1737 0.2268 0.2993 0.3741
1.9466 −2.6742 0.2125 1.0993 −0.4176 −2.2859 2.0611 −1.7565 2.8122 −1.9236 0.4187 −1.0430 2.8612 −2.5516 0.2756 0.5866 −0.2147 −2.5848 0.3886 2.4208 −1.5196 0.0332 0.1231
Table 3. Dissolution Enthalpy and Entropy for Correlation eq 5 of (2S)-Pyrrolidine-2-carboxylic Acid in Pure Alcohols (Ethanol, Butan-1-ol, and Isopropyl Alcohol) and Methanol from 298.15 K to 348.15 K and from 291.15 K to 331.15 K, Respectively solvent
ΔSs0/(J mol−1 K−1)
ΔHs0/(KJ mol−1)
R2
methanol ethanol butan-1-ol isopropyl alcohol
30.1865 48.43831 24.94295 31.89075
16.0995 27.8969 22.5081 27.1337
0.9957 0.9969 0.9924 0.9915
> ethanol > butan-1-ol > isopropyl alcohol, which could be well explained by the principle that the polar solutes are more soluble in polar solvents and nonpolar molecules are soluble in nonpolar (mostly organic) solvents. The temperature dependence of (2S)-pyrrolidine-2-carboxylic acid solubility was described by the modified Apelblat equation.7,8 The modified Apelblat equation is B ln x1 = A + + C ln(T /K) (3) T /K where x1 is the mole fraction solubility of (2S)-pyrrolidine-2carboxylic acid, T is the absolute temperature (K), A, B, and C are the parameters determined by the experimental solubility data, and the deviation (dev. %) is listed in Table 2. The deviation is
a
dev. (%) =
Standard uncertainties u are u(T) = 0.05 K, ur(p) = 0.05, ur(x1) = 0.02. B
100 n
∑
[x cal − x exp] x exp
(4)
DOI: 10.1021/je5007949 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 4. Experimental Mole Fraction Solubilities x1 of (2S)-Pyrrolidine-2-carboxylic Acid in Binary Alcohols (x2)−Water (1 − x2) Mixtures at Temperature T and Pressure p = 0.1 MPaa x2b
solvent methanol
0
0.1998
0.4001
0.6018
0.7998
1
ethanol
0
0.2012
0.3987
0.5913
a
T/K
102x1
100(x1 − xcal/x1)
291.15 301.15 311.15 321.15 331.15 291.15 301.15 311.15 321.15 331.15 291.15 301.15 311.15 321.15 331.15 291.15 301.15 311.15 321.15 331.15 291.15 301.15 311.15 321.15 331.15 291.15 301.15 311.15 321.15 331.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15
19.6125 22.1423 24.4402 26.3950 28.0041 20.6082 23.1487 25.0575 26.7140 28.3239 20.1765 21.3501 22.7706 24.0535 26.3112 16.2304 17.5797 19.0717 20.7983 22.9580 10.9712 12.3418 13.9977 15.9714 18.0452 4.8897 5.9700 7.6104 9.2507 10.7051 21.4083 23.7844 25.8543 27.5584 28.8840 29.8125 21.6107 24.0583 27.0922 28.9178 31.7831 33.4908 18.6303 21.0225 22.4162 24.4412 26.8668 27.8299 13.6878 14.9782 16.1812
0.0065 −0.0258 0.0288 −0.0184 0.0024 −0.3590 0.6281 −0.0464 −0.4415 0.2178 −0.2514 0.2590 0.5713 −0.9296 0.3294 −0.1499 0.2451 0.0538 −0.2561 0.1017 0.2212 −0.2927 −0.1820 0.3830 −0.1376 1.9314 −2.6889 0.1994 1.0856 −0.4325 −0.0070 0.0041 0.0113 −0.0124 −0.0031 0.0031 0.2726 −0.7201 1.0219 −1.1736 0.8300 −0.2440 −0.2637 1.3242 −1.4247 −0.7590 1.7543 −0.7001 0.0146 0.6205 −1.0757
x2b
solvent
0.7952
1
isopropyl alcohol
0
0.1987
0.4014
0.6011
0.7924
1
T/K
102x1
100(x1 − xcal/x1)
328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15 298.15 308.15 318.15 328.15 338.15 348.15
18.0998 20.4355 22.6760 5.1337 6.5175 7.9634 9.5973 11.0820 13.0785 0.4472 0.6423 0.8521 1.2314 1.6217 2.2925 21.4083 23.7844 25.8543 27.5584 28.8840 29.8125 19.8013 23.0797 25.3829 27.2007 29.1222 30.9061 13.9011 16.9199 19.8948 21.7261 23.3153 24.8915 7.9172 10.5117 12.4546 14.1668 15.6458 16.8601 2.1852 3.1203 3.9569 4.791 5.6684 6.2426 0.0767 0.1192 0.1737 0.2268 0.2993 0.3741
−0.1593 0.9237 −0.3709 −0.8965 0.5118 0.3171 0.7454 −1.3084 0.4558 −2.2458 2.0532 −1.7923 2.7689 −1.9625 0.4010 −0.0070 0.0041 0.0113 −0.0124 −0.0031 0.0031 −1.2078 1.4405 0.5824 −0.8468 −0.5500 0.4836 −0.7982 0.0527 1.5969 −0.5328 −1.1425 0.6632 −2.2449 2.1879 0.4826 −0.6926 −0.6988 0.5104 −1.5541 1.8771 −0.1271 −1.0900 0.7089 −0.1451 −2.6000 0.3933 2.4336 −1.5078 0.0346 0.1066
Standard uncertainties u are u(T) = 0.05 K, ur(p) = 0.05, ur(x1) = 0.02. bAccuracy ± 0.0001.
where xexp and xcal are the experimental and calculated values by eq 3, respectively, n is the number of experimental points. As evident, the solubility of (2S)-pyrrolidine-2-carboxylic acid in pure solvents was correlated with the modified Apelblat equation.
The apparent molar enthalpies of solution could be described as the Van’t Hoff equation.9,10 ln x1 = − C
ΔHs0 ΔSs0 + RT R
(5) DOI: 10.1021/je5007949 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 3. Mole fraction solubility of (2S)-pyrrolidine-2-carboxylic acid in binary methanol (x2)−water (1 − x2) from 291.15 K to 331.15 K: ■, x2 = 0; ●, x2 = 0.1998; ▲, x2 = 0.4001; ▼, x2 = 0.6018; ◆, x2 = 0.7998; ◀, x2 = 1.
Figure 5. Mole fraction solubility of (2S)-pyrrolidine-2-carboxylic acid in binary isopropyl alcohol (x2)−water (1 − x2) from 298.15 K to 348.15 K: ■, x2 = 0; ●, x2 = 0.1987; ▲, x2 = 0.4014; ▼, x2 =0.6011; ◆, x2 = 0.7924; ◀, x2 = 1.
Figure 4. Mole fraction solubility of (2S)-pyrrolidine-2-carboxylic acid in binary ethanol (x2)−water (1 − x2) from 298.15 K to 348.15 K: ■, x2 = 0; ●, x2 = 0.2012; ▲, x2 = 0.3987; ▼, x2 = 0.5913; ◆, x2 = 0.7952; ◀, x2 = 1.
Figure 6. Van’t Hoff plots of ln x1 verse 1/T in binary methanol (x2)− water (1 − x2) from 291.15 K to 331.15 K: ■, x2 = 0; ●, x2 = 0.1998; ▲, x2 = 0.4001; ▼, x2 = 0.6018; ◆, x2 = 0.7998; ◀, x2 = 1.
(2S)-pyrrolidine-2-carboxylic acid in the mixtures of alcohols and water was a function of temperature and alcohols composition. The solubility of (2S)-pyrrolidine-2-carboxylic acid in the binary mixtures of alcohols and water increases with increasing temperature and decreasing of the proportion of alcohols. The combined nearly ideal binary solvent/Redlich−Kister (CNIBS/R-K) model was proposed.11−13 This model describes the solubility of the crystalline solute dissolved in the mixture solvents:
where x1 is mole fraction solubility of (2S)-pyrrolidine-2carboxylic acid, ΔH0s and ΔS0s are the apparent molar enthalpy and entropy of solution, R is the gas constant, T is the absolute temperature. The linear fits of ln x1 in pure solvents against 1/T were plotted in Figure 2. The values of and ΔH0s and ΔS0s were calculated with the slope and the intercept of the straight line (Table 3). The standard enthalpy and entropy of dissolution for pure organic solvents are positive. The dissolving process is endothermic and the dissolution driving force converts from enthalpy-driving to entropy-driving. 3.2. Binary Solvent Mixtures. The solubility of (2S)pyrrolidine-2-carboxylic acid in the binary systems of water and alcohols (methanol, ethanol, and isopropyl alcohol) was measured at different temperatures, which were showed in Table 4 and Figures 3, 4, and 5. The mole fraction solubility of (2S)pyrrolidine-2-carboxylic acid in water is 0.2141 (15.12 mol/kg) at temperature 298.15 K and pressure 0.1 MPa, which is similar to that of Held’s result (15.35 ± 0.15).5 From the experimental values (Table 4), we could know that the solubility of
N
ln x1 = x 2 ln(x1)2 + x3 ln(x1)3 + x 2x3 ∑ Si(x 2 − x3)i i=0
(6)
where Si is the model constant and N can vary from 0 to 3. x2 and x3 are mole fractions of the components in binary mixtures calculated in the absence of solute. (x1)i is the saturated mole fraction solubility of the solute in pure solvent i. When N = 2, eq 6 can be rearranged into eq 7. ln x1 = B0 + B1x 2 + B2 x 22 + B3x 23 + B4 x 24 D
(7)
DOI: 10.1021/je5007949 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 5. Parameters for Correlation eq 7 of (2S)-Pyrrolidine-2-Carboxylic Acid in Binary Methanol (x2)−Water (1 − x2) Mixtures from 291.15 K to 331.15 K T/K
B0
B1
B2
B3
B4
dev. %
291.15 301.15 311.15 321.15 331.15
−1.6301 −1.5079 −1.4090 −1.3318 −1.2730
0.4304 0.7273 0.6222 0.5891 0.4562
−0.6258 −3.1471 −3.1830 −3.5773 −2.6095
−0.5891 3.7922 4.0066 5.1238 3.6618
−0.5867 −2.6799 −2.6123 −3.1862 −2.4690
1.0972 0.2277 0.0162 0.2112 0.1305
Table 6. Parameters for Correlation eq 7 of (2S)-Pyrrolidine-2-Carboxylic Acid in Binary Ethanol (x2)−Water (1− x2) Mixtures from 298.15 K to 348.15 K T/K
B0
B1
B2
B3
B4
dev. %
298.15 308.15 318.15 328.15 338.15 348.15
−1.5413 −1.4365 −1.3532 −1.2895 −1.2424 −1.2101
0.9652 0.7231 1.6261 1.5740 2.0663 2.4800
−6.8188 −4.4852 −9.6439 −9.2188 −11.0253 −13.5287
13.5066 7.5112 16.0807 15.4610 18.2197 23.1161
−11.6802 −7.0824 −11.2101 −10.7004 −12.0211 −14.6583
2.5729 5.9558 5.8093 5.1004 2.6770 0.5738
Table 7. Parameters for Correlation eq 7 of (2S)-Pyrrolidine-2-Carboxylic Acid in Binary Isopropyl Alcohol (x2)−Water (1 − x2) Mixtures from 298.15 K to 348.15 K T/K
B0
B1
B2
B3
B4
dev. %
298.15 308.15 318.15 328.15 338.15 348.15
−1.5414 −1.4361 −1.3527 −1.2889 −1.2419 −1.2102
1.1850 1.6514 1.1007 1.1180 1.3827 1.6303
−11.5608 −13.4375 −8.6987 −8.7209 −9.8466 −10.5470
21.6000 25.8836 16.2656 16.6561 18.4735 19.3192
−17.0149 −19.7305 −13.6472 −13.8166 −14.5424 −14.8238
2.4684 4.8044 0.3991 0.6314 0.6396 0.7225
Figure 7. Van’t Hoff plots of lnx1 verse 1/T in binary ethanol (x2) water (1-x2) from 298.15K to 348.15K: ■, x2 = 0; ●, x2 = 0.2012; ▲, x2 = 0.3987; ▼, x2 = 0.5913; ◆, x2 = 0.7952; ◀, x2 = 1.
Figure 8. Van’t Hoff plots of lnx1 verse 1/T in binary isopropyl alcohol (x2) - water (1-x2) from 298.15K to 348.15K: ■, x2 = 0; ●, x2 = 0.1987; ▲, x2 = 0.4014; ▼ , x2 = 0.6011; ◆, x2 = 0.7924; ◀, x2 = 1.
B0, B1, B2, B3, and B4 are parameters of this model, which are obtained by least-squares analysis of the experimental solubility data and listed in Tables 5, 6, and 7 along with the dev. %. The CNIBS/R-K model can be used to describe the solubility values and to predict solubility values for different concentrations of the mixtures at a fixed temperature. The Van’t Hoff plots of the mole fraction solubility (ln (x1)) of (2S)-pyrrolidine-2-carboxylic acid in binary mixed solvents versus 1/T with a straight line are shown in Figures 6, 7, and 8. The solution enthalpy and entropy of (2S)-pyrrolidine-2-carboxylic acid in the binary system of aqueous alcohols (methanol,
ethanol, and isopropyl alcohol) as shown in Table 8, 9, and 10 were calculated as previous described in section 3.1. The dissolution process of (2S)-pyrrolidine-2-carboxylic acid in the binary system was endothermic (ΔH0s > 0) and entropy-driving (ΔH0s > 0, ΔS0s > 0).
4. CONCLUSION The solubility of (2S)-pyrrolidine-2-carboxylic acid in pure solvents follows the order methanol > ethanol > butan-1-ol > isopropyl alcohol. The solubility of (2S)-pyrrolidine-2-carboxylic acid in the water and alcohols (methanol, ethanol, and isopropyl E
DOI: 10.1021/je5007949 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 8. Dissolution Enthalpy and Entropy for Correlation eq 5 of (2S)-Pyrrolidine-2-carboxylic Acid in Binary Methanol (x2)−Water (1 − x2) Mixtures from 291.15 K to 331.15 K x2
ΔS0s /(J mol−1 K−1)
ΔH0s /(KJ mol−1)
R2
0 0.1998 0.4001 0.6018 0.7998 1
11.1388 8.5577 4.4458 8.4644 15.9883 30.1861
7.1507 6.2758 5.1934 6.8909 10.0323 16.0993
0.9867 0.9840 0.9796 0.9913 0.9966 0.9957
ΔS0s /(J mol−1 K−1)
ΔH0s /(KJ mol−1)
R2
0 0.2012 0.3987 0.5913 0.7952 1
6.5801 13.0182 9.6166 12.6644 29.0171 48.4383
5.7246 7.6529 7.0007 8.7652 15.9632 27.8969
0.9698 0.9916 0.9879 0.9835 0.9974 0.9969
Table 10. Dissolution Enthalpy and Entropy for Correlation eq 5 of (2S)-Pyrrolidine-2-carboxylic Acid in Binary Isopropyl Alcohol (x2)−Water (1 − x2) Mixtures from 298.15 K to 348.15 K x2
ΔS0s /(J mol−1 K−1)
ΔH0s /(KJ mol−1)
R2
0 0.1987 0.4014 0.6011 0.7924 1
6.5801 11.7491 17.1268 22.1568 29.1705 31.8908
5.7246 7.4329 9.8675 12.7046 17.9751 27.1337
0.9698 0.9738 0.9539 0.9524 0.9701 0.9915
alcohol) mixtures decreased with decreasing temperature and water proportion. The experimental data of (2S)-pyrrolidine-2carboxylic acid in pure solvents and aqueous alcohols mixtures can be well-regressed by the modified Apelblat equation and the CNIBS/R-K model, respectively. On the basis of the experimental data, the dissolving enthalpy and entropy in all pure solvents and the binary solvent mixtures were calculated by the Van’t Hoff equation. The positive standard molar enthalpy of dissolution indicated the process was endothermic and entropy-driven.
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Table 9. Dissolution Enthalpy and Entropy for Correlation eq 5 of (2S)-Pyrrolidine-2-carboxylic Acid in Binary Ethanol (x2)−Water (1 − x2) Mixtures from 298.15 K to 348.15 K x2
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[email protected]. Fax: +86-311-81668436. Funding
This research is supported by Natural Science Foundation of China (No. 21106033), Science and Technology Department of Hebei (No. B2012208037), Hebei Education Department (No. BJ2014024, Y2011107, 2011167 and Q2012062), and Hebei University of Science and Technology (No. XL201227 and SW27). Notes
The authors declare no competing financial interest. F
DOI: 10.1021/je5007949 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
