Measurement and Correlation of Solubilities of Indole-2-carboxylic

Nov 8, 2013 - College of Chemistry and Chemical Engineering Luoyang Normal University, Luoyang, 471022 P. R. China. ABSTRACT: The solubilities of ...
0 downloads 0 Views 300KB Size
Download PDF
Article pubs.acs.org/jced

Measurement and Correlation of Solubilities of Indole-2-carboxylic Acid in Ten Different Pure Solvents from (278.15 to 360.15) K Jin-Qiang Liu,* Xin-Xiang Cao, Baoming Ji, and Bangtun Zhao College of Chemistry and Chemical Engineering Luoyang Normal University, Luoyang, 471022 P. R. China ABSTRACT: The solubilities of indole-2-carboxylilc acid in ten pure solvents including water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, ethyl acetate, dichloromethane, toluene, and 1,4-dioxane were measured from (278.15 to 360.15) K at atmospheric pressure using the synthetic method. The solubility was determined by a laser monitoring observation technique and found to increase with the rise of temperature. The experimental solubilities were regressed by the modified Apelblat with a relative deviation less than 3.63 % except in toluene.

■

INTRODUCTION Indole-2-carboxylic acid (I2CA, C9H7NO2, CAS registry no. 1477-50-5, molecular weight 161), with its chemical structure shown in Figure 1, is a versatile intermediate in the synthesis of

(HPLC) to be 0.998 in mass fraction. Deionized water (with the electrical conductivity of < 2·10−6 S) was used in our experiment. Organic solvents are of analytic pure (> 99.5 % in mass fraction), purchased from Tianjin Yongda Chemical Reagent Co., Ltd. of China, were dried and stored over 3 Å molecular sieves and were used without further purification. The mass fraction of water in organic solvents was less than 0.002, as determined by the Karl Fischer method. Apparatus and Procedure. The solubility was measured by a synthetic method. In our previous work, our co-worker had explained the procedure in detail,15,16 and little improvement was made. All of the apparatuses including composition and type were exactly the same as with our previous work.15,16 Our solubility apparatus included an ∼ 200 mL jacketed glass vessel, a thermostat, a magnetic stirrer, and a mercury-in-glass thermometer (uncertainty of ± 0.05 K). A laser beam was employed to observe the dissolution of the solid + liquid mixture. The light signal transmitted through the vessel was collected by a detector to guarantee the dissolution of the last crystal, and the equilibrium point of the given system was estimated on the basis of the signal change. At the beginning, a known mass of solute was added to a known mass of solvent at a known temperature. The mass of solute and solvent was determined by an electronic analytical balance (type BS210S, Sartorius Scientific Instrument Co. Ltd.) with an uncertainty of less than 0.0001 g. The undissolved solid particles were completely suspended in the jacketed vessel by continuous stirring for 60 min, and then a quantitative additional solvent was added into the vessel through a buret. The intensity of the penetrated light increased with the increase of the amount of solvent in the vessel, and the penetrated light intensity reached its maximum value when the last portion of the solid solute just disappeared. Then the mass of the solute and the total solvent were recorded. The saturated mole fraction solubility (x1) would be obtained from the mass of the solute and solvent with their molecular weight. All of the experiments were run at least three times, and the relative uncertainties of the experimental data were within 1 %,

Figure 1. Chemical structure of indole-2-carboxylic acid.

medical1−8 and natural products.9−12 After it was found to be a competitive antagonist of potentiation by glycine at the NMDA receptor,13 the syntheses of I2CA and its derivatives have been attracting the organic synthetic chemists’ attention for a long time. Ever since the first synthetic route to I2CA, several procedures have been developed in the last century.14 Among all of these synthetic methods, the Fischer indole synthesis, although an old one, is classic and is thought to be the best method so far considering raw-material avaibility, reaction conditions, yield and operational simplicity.14 In view of the central role of I2CA in the synthesis of various medical products, to obtain I2CA with high purity, it is very necessary to find a suitable solvent for its separation and subsequent recrystillization. Thus, the accurate solubilities of I2CA in pure solvent are needed to design the separation process. Unfortunately, no accurate solubilities of I2CA in pure solvent have been reported in the literature so far. In this study, using a laser monitoring observation technique, the solubilities of I2CA in water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, ethyl acetate, 1,2-dichloromethane, toluene, and 1,4dioxane were measured at temperatures ranging from (278.15 to 360.15) K by a synthetic method. Also, the experimental solubility data were correlated with the modified Apelblat equation, and the solubilities correlated by model agreed with the experimental data.

■

EXPERIMENTAL SECTION Materials. An off-white crystalline powder of I2CA (C9H7NO2, melting point 480.15 K20) was obtained from Ningbo Wusheng Chemical Co., Ltd. It was further purified by recrystallizing from the solution of methanol two times, and its purity was measured by high-performance liquid chromatography © 2013 American Chemical Society

Received: February 1, 2013 Accepted: October 23, 2013 Published: November 8, 2013 3309

dx.doi.org/10.1021/je400813d | J. Chem. Eng. Data 2013, 58, 3309−3313

Journal of Chemical & Engineering Data

Article

Table 1. Comparison of the Solubility Data of NaCl in Water between Literature (xref) and Our Experiment (x), at Temperature T and Pressure p = 0.1 MPa T/K

x/g (100 g of water)−1

xref/g (100 g of water)−1

100(x − xref)/x

100 1/n ∑|((x − xref)/x)|

293.15 303.15 313.15 323.15 333.15

36.08 36.32 36.66 37.05 37.34

36.0 36.3 36.6 37.0 37.3

0.222 0.055 0.164 0.135 0.107

0.137

Figure 2. Mole fraction solubilities x1 in different solvents: ■, methanol; ●, ethanol; ▴, 1-propanol; , solubility curve calculated from the modified Apelblat equation.

Figure 3. Mole fraction solubilities x1 in different solvents: ▽, 2-propanol; ◇, 1-butanol; □, ethyl acetate; , solubility curve calculated from the modified Apelblat equation.

could be utilized as the proper solvent in the recrystillization of I2CA for high quality production. The solubilities of I2CA in different alcohols and ethyl acetate seem likewise. That might be the result of their structural similarity. All of them are composed of a hydroxyl functional group and relative short alkyl chain except ethyl acetate. The hydroxyl group in alcohols and the carbonyl group in ethyl acetate make it possible to form hydrogen bond, which could be the major reason for their similar solubility. To further understand the different solubility behavior of I2CA in different solvents, we examined the solvent properties including polarity, dipole moments, dielectric constants, and δ Hildebrand solubility parameters. However, no principle has been found. For instance, the polarity of alcohols is in the range of 54.6−76.2 but that of ethyl acetate is only 23. Thus, the polarity of the solvent is not the only reason for the solubility behavior. The same situation lies in the solubility parameter, dipole moments, and dielectric constants. All these data indicate a net contribution to the solubility behavior. Data Correlation. Modified Apelblat Equation. The modified Apelblat equation has been widely used in the correlation of solubility data of different substances due to its simplicity.18,19 Hence, the temperature dependence of solubility of I2CA in different pure solvents was correlated with the modified Apelblat equation (1):

obtained from the mass ratio of the additional solute to the dissolved solute.

■

RESULTS AND DISCUSSION Experimental Solubility Data. The accuracy of the experimental method described above was confirmed by comparing our solubility data of sodium chloride in water with those in literature.17 Our experimental data, together with literature values, were gathered in Table 1. These data demonstrated that our experimental method was accurate and reliable. The measured solubilities data of I2CA in different solvents at different temperatures are presented in Table 2, where T represents the absolute temperature and x1 and xcal,Apel are the solubility of the experimental and calculated values from the modified Apelblat equation, respectively. For clearness, the plot of the solubility data of I2CA in these solvents at the temperature range of (278.15−360.15) K was shown in Figures 2, 3, and 4. The solubility curves of I2CA in methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol are likewise and thus are collected in one figure, while that in water, 1,4-dioxane, dichloromethane, and toluene are drawn in another figure. From Table 2 and Figures 2, 3, and 4, it can be seen that the solubility of I2CA in all selected solvents increases with the increase of temperature, and it is also shown that the solubility of I2CA is very high in high polar organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and ethyl acetate) and low in water and low polar organic solvents (toluene, dichloromethane, and 1,4-dioxane). Furthermore, the solubility in toluene varies much more obviously with temperature than in the other solvents, which may show its potential advantage in the recrystillization of I2CA. In addition, the crystal obtained from water is needlelike and that from other solvents is off-white powder, which might imply that toluene

ln x1cal,Apel = A + B /T + C ln T

(1)

cal,Apel

where x1 is the calculated mole fraction solubility of I2CA; T is the absolute temperature; and A, B, and C are the empirical model parameters. The values of A and B represent the variation in the solution activity and the solution behavior resulting from the nonidealities of solution. The value of C stands for the relationship between the temperatures and the enthalpy of fusion. 3310

dx.doi.org/10.1021/je400813d | J. Chem. Eng. Data 2013, 58, 3309−3313

Journal of Chemical & Engineering Data

Article

Table 2. Solubilities (x1) and Calculated (xcalcd,Apel) Values of I2CA in Different Solvents at Temperature T = (278.15 to 360.15) K at Pressure p = 0.1 MPaa T/K 293.15 298.15 303.15 308.05 312.65 318.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15 358.15

104x1 0.679 0.688 0.703 0.717 0.788 0.936 1.153 1.487 2.001 2.805 4.085 6.163 9.617 15.485

278.15 283.35 288.95 293.25 298.15 303.35 307.85 312.95 317.75 323.15 328.25 333.15

679.1 695.4 723.2 752.0 855.6 924.9 1024.7 1184.8 1351.4 1591.2 1887.3 2296.2

278.15 283.15 287.95 292.75 297.95 303.05 308.35 313.25 318.65 324.95 329.85 336.25 342.75 348.25 353.15

569.4 619.9 666.1 701.1 779.9 815.6 880.9 974.4 1022.4 1163.3 1197.5 1349.5 1476.6 1544.5 1651.7

278.25 285.45 291.35 298.15 305.75 311.25 317.75 322.15 328.05 333.55 339.15 344.85 349.75 353.15 358.15

437.4 521.3 587.9 680.2 800.6 880.2 992.9 1048.0 1148.3 1275.1 1379.4 1509.2 1616.0 1762.1 1796.3

104xcalcd,Apel Water 0.718 0.676 0.677 0.718 0.794 0.948 1.171 1.512 2.036 2.849 4.137 6.217 9.648 15.434 Methanol 680.3 695.8 731.8 773.8 838.7 930.5 1032.7 1179.7 1355.5 1608.2 1915.4 2291.7 Ethanol 575.9 620.9 667.1 716.5 773.7 833.7 900.6 966.7 1044.5 1142.4 1224.1 1338.7 1464.8 1579.7 1688.6 1-Propanol 433.6 512.4 583.1 671.8 780.0 864.3 970.3 1046.0 1152.4 1256.5 1367.3 1485.0 1589.9 1664.8 1777.7

100(x1 − xcalcd,Apel)/x1

T/K

−5.79 1.77 3.65 −0.12 −0.74 −1.29 −1.59 −1.74 −1.73 −1.58 −1.28 −0.86 −0.33 0.32

278.35 285.15 291.05 298.15 305.55 310.15 315.75 321.35 328.65 333.35 338.75 342.25 348.15 353.25 358.15

411.8 525.1 605.7 701.4 855.4 948.5 1079.0 1185.7 1311.8 1489.6 1605.8 1713.3 1905.0 2008.8 2188.3

278.15 285.35 291.05 298.55 305.25 310.75 315.15 321.75 328.35 333.95 338.15 342.45 348.25 353.45 358.15

478.3 538.2 605.5 686.5 758.1 831.6 908.6 1014.0 1120.0 1247.3 1401.4 1425.3 1598.3 1737.5 1901.1

284.05 290.45 294.65 299.55 304.65 309.35 313.95 318.65 324.35 328.75 333.65

432.7 600.3 735.2 865.2 1004.9 1078.5 1164.4 1214.0 1277.4 1338.9 1400.2

−0.18 −0.06 −1.19 −2.90 1.98 −0.61 −0.78 0.42 −0.31 −1.07 −1.49 0.20 −1.15 −0.16 −0.16 −2.20 0.80 −2.22 −2.23 0.79 −2.16 1.80 −2.23 0.80 0.80 −2.28 −2.24 0.85 1.71 0.81 1.24 2.57 1.80 2.27 0.19 −0.36 1.45 0.87 1.60 1.61 5.52 1.03

286.35 291.25 297.05 301.95 306.95 312.15 317.25 321.65 326.55 331.95 336.65 283.15 287.15 292.75 3311

104x1

27.57 34.34 42.66 47.57 51.96 59.21 63.65 68.86 72.81 79.05 86.61 6.841 7.237 8.733

104xcalcd,Apel 2-Propanol 424.0 514.7 602.8 720.5 856.8 948.4 1067.0 1193.1 1368.3 1487.3 1629.6 1724.9 1890.5 2038.3 2184.0 1-Butanol 475.1 537.1 592.2 673.6 756.1 831.4 897.0 1005.1 1126.3 1240.2 1333.0 1435.0 1584.8 1731.8 1876.0 Ethyl Acetate 442.9 600.2 710.7 841.4 972.7 1083.3 1176.8 1252.9 1314.6 1337.8 1338.4 1,4-Dioxane 27.87 33.06 39.59 45.33 51.26 57.37 63.16 67.90 72.79 77.60 81.22 Dichloromethane 6.663 7.482 9.036

100(x1 − xcalcd,Apel)/x1 −2.96 1.98 0.48 −2.72 −0.16 0.01 1.11 −0.63 −4.31 0.151 −1.48 −0.68 0.76 −1.47 0.19 0.68 0.21 2.20 1.87 0.27 0.03 1.28 0.88 −0.56 0.57 4.88 −0.68 0.85 0.32 1.32 −2.38 0.02 3.33 2.76 3.20 −0.45 −1.07 −3.20 −2.92 0.08 4.41 −1.09 3.72 7.18 4.71 1.34 3.11 0.77 1.40 0.03 1.83 6.23 2.60 −3.38 −3.47

dx.doi.org/10.1021/je400813d | J. Chem. Eng. Data 2013, 58, 3309−3313

Journal of Chemical & Engineering Data

Article

Table 2. continued 104x1

T/K

a

295.65 299.05 302.65 307.25 313.15

10.352 11.893 13.355 16.823 22.396

287.85 293.65 297.95 302.85

5.204 6.448 7.216 7.861

104xcalcd,Apel Dichloromethane 10.078 11.563 13.515 16.744 22.550 Toluene 5.457 6.243 6.973 7.993

100(x1 − xcalcd,Apel)/x1

T/K

2.64 2.78 −1.20 0.47 −0.69

307.05 311.55 313.55 317.45 325.15 337.85 342.55 348.25 360.15

−4.86 3.18 3.37 −1.68

104x1

104xcalcd,Apel

8.983 9.885 10.377 11.304 15.526 29.500 37.934 42.700 64.239

Toluene 9.061 10.446 11.155 12.734 16.794 27.579 33.505 42.729 72.626

100(x1 − xcalcd,Apel)/x1 −0.86 −5.67 −7.50 −12.65 −8.16 6.51 11.68 −0.07 −13.05

The standard uncertainty u is u(T) = 0.01 K; the relative standard uncertainty u is ur(x) = 0.07.

Table 3. Parameters of the Modified Apelblat Equation for I2CA in Different Solvents solvent

A

B

C

R2

100rmsrdApel

water methanol ethanol 1-propanol 2-propanol 1-butanol Ethyl acetate 1,4-dioxane dichloromethane toluene

−1454.6898 −487.9156 −44.9157 19.6354 48.0661 −70.0365 602.4414 271.3629 −663.0357 −382.6293

64757.93 20233.84 773.55 −2526.04 −4091.52 1695.72 −29436.07 −14477.34 26104.99 14679.91

215.5086 73.2883 6.9754 −2.4309 −6.4905 10.8210 −88.8496 −40.0658 99.8104 57.2364

0.999 0.999 0.999 0.999 0.999 0.999 0.993 0.993 0.994 0.990

2.17 1.25 1.68 2.01 1.77 1.60 2.60 3.63 2.42 7.41

where N represents the number of experimental points, xcal i is the mole fraction solubility calculated from eq 1, and xi is the experimental value. It is seen from Table 3 that the calculated solubilities by the modified Apelblat are in good agreement with the experimental values in most cases. The 100rmsrd is always less than 3.63 % with modified Apelblat equation except for toluene (7.41 %).

■

CONCLUSIONS The solubilities of I2CA in water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, ethyl acetate, 1,4-dioxane, dichloromethane, and toluene have been determined from (278.15 to 360.15) K by a synthetic method. The solubilities in all selected solvents increase with the rise of temperature. The modified Apelblat based on solid−liquid phase equilibrium principles is used to correlate the solubility data of I2CA in these solvent systems. The rmsrd among these values does not exceed 7.4 % for the modified Apelblat equation, and the solubility calculated by the model shows good agreement with the experimental data.

Figure 4. Mole fraction solubilities 104x1 in different solents: ☆, water; ○, 1,4-dioxane; ×, dichloromethane; +, toluene; , solubility curve calculated from the modified Apelblat equation.

■

The adjustable parameters A, B, and C in the modified Apelblat equation can be obtained from simplex optimization. Particularly, the values of A, B, and C in modified Apelblat equation were presented in Table 3. The room-mean-square relative deviations (rmsrd) for each equation were calculated with eq 2 and listed together with the equation parameters in Table 3. ⎡ 1 rmsrd = ⎢ ⎢N ⎣

1/2 ⎛ x cal − x ⎞2 ⎤ i i ⎥ ⎟⎟ ∑ ⎜⎜ xi ⎠ ⎥⎦ 1 ⎝

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +86-379-65515113. Fax: +86-65523821. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. J.-Q.L. measured and correlated the data and wrote this paper, X.-X.C. correlated the data, and B.-M.J. and B.-T.Z. provided the solvents, discussed the data, and read this paper.

N

(2) 3312

dx.doi.org/10.1021/je400813d | J. Chem. Eng. Data 2013, 58, 3309−3313

Journal of Chemical & Engineering Data

Article

Funding

(16) Cao, X. X.; Liu, J. Q.; Lv, T. T.; Yao, J. C. Solubility of 6Chloropyridazin-3-amine in Different Solvents. J. Chem. Eng. Data 2012, 57, 1509−1514. (17) Zhang, L.; Huang, Z. P.; Wan, X. R.; Li, J.; Liu, J. Measurement and Correlation of the Solubility of Febuxostat in Four Organic Solvents at Various Temperatures. J. Chem. Eng. Data 2012, 57, 3149− 3152. (18) Apelblat, A.; Manzurola, E. Solubilities of o-acetylsalicylic, 4aminosalicylic, 3,5-dinitrosalicylic, p-toluic acid and magnesium-DLaspartate in water from T= (278 to 348)K. J. Chem. Thermodyn. 1999, 31, 85−91. (19) Manzurola, E.; Apelblat, A. Solubilities of l-glutamic acid, 3nitrobenzoic acid, p-toluic acid, calcium-l-lactate, calcium gluconate, magnesium-dl-aspartate, and magnesium-l-lactate in water. J. Chem. Thermodyn. 2002, 34, 1127−1136. (20) Brehm, W. J. Derivatives of Indole-2-Carboxylic Acid. J. Am. Chem. Soc. 1949, 71, 3541−3542.

This work was financially funded by the National Natural Science Foundation of China (Nos. 21172105, 21072089, and 21073082) and Natural Science Foundation of Henan Province (No. 132300410319). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Silvano, E.; Millan, M. J.; la Cour, C. M.; Han, Y.; Duan, L. H.; Griffin, S. A.; Luedtke, R. R.; Aloisi, G.; Rossi, M.; Zazzeroni, F.; Javitch, J. A.; Maggio, R. The Tetrahydroisoquinoline Derivative SB269,652 Is an Allosteric Antagonist at Dopamine D-3 and D-2 Receptors. Mol. Pharmacol. 2010, 78, 925−934. (2) Potter, A. J.; Ray, S.; Gueritz, L.; Nunns, C. L.; Bryant, C. J.; Scrace, S. F.; Matassova, N.; Baker, L.; Dokurno, P.; Robinson, D. A.; Surgenor, A. E.; Davis, B.; Murray, J. B.; Richardson, C. M.; Moore, J. D. Structure-guided design of alpha-amino acid-derived Pin1 inhibitors. Bioorg. Med. Chem. Lett. 2010, 20, 586−590. (3) Mayes, B. A.; Chaudhuri, N. C.; Hencken, C. P.; Jeannot, F.; Latham, G. M.; Mathieu, S.; McGarry, F. P.; Stewart, A. J.; Wang, J. Y.; Moussa, A. Robust Synthesis of Methyl 5-Chloro-4-fluoro-1H-indole2-carboxylate: A Key Intermediate in the Preparation of an HIV NNRTI Candidate. Org. Process Res. Dev. 2010, 14, 1248−1253. (4) Guo, Z. Y.; Ji, Z. Q.; Zhang, J. W.; Deng, J.; Shen, L.; Liu, W.; Wu, W. J. NW-G01, a novel cyclic hexapeptide antibiotic, produced by Streptomyces alboflavus 313: II. Structural elucidation. J. Antibiot. 2010, 63, 231−235. (5) Mandal, P. K.; Limbrick, D.; Coleman, D. R.; Dyer, G. A.; Ren, Z. Y.; Birtwistle, J. S.; Xiong, C. Y.; Chen, X. M.; Briggs, J. M.; McMurray, J. S. Conformationally Constrained Peptidomimetic Inhibitors of Signal Transducer and Activator of Transcription 3: Evaluation and Molecular Modeling. J. Med. Chem. 2009, 52, 2429−2442. (6) Fritsche, A.; Elfringhoff, A. S.; Fabian, J.; Lehr, M. 1-(2Carboxyindol-5-yloxy)propan-2-ones as inhibitors of human cytosolic phospholipase A(2)alpha: Synthesis, biological activity, metabolic stability, and solubility. Bioorg. Med. Chem. 2008, 16, 3489−3500. (7) Zhang, H. Z.; Drewe, J.; Tseng, B.; Kasibhatla, S.; Cai, S. X. Discovery and SAR of indole-2-carboxylic acid benzylidene-hydrazides as a new series of potent apoptosis inducers using a cell-based HTS assay. Bioorg. Med. Chem. 2004, 12, 3649−3655. (8) Reddy, B. V. S.; Reddy, M. R.; Rao, Y. G.; Yadav, J. S.; Sridhar, B. Cu(OTf)2-Catalyzed Synthesis of 2,3-Disubstituted Indoles and 2,4,5Trisubstituted Pyrroles from α-Diazoketones. Org. Lett. 2013, 15, 464−467. (9) Qi, S. H.; Miao, L.; Gao, C. H.; Xu, Y.; Zhang, S.; Qian, P. Y. New Steroids and a New Alkaloid from the Gorgonian Isis minorbrachyblasta: Structures, Cytotoxicity, and Antilarval Activity. Helv. Chim. Acta 2010, 93, 511−516. (10) Capon, R. J.; Peng, C.; Dooms, C. Trachycladindoles A-G: cytotoxic heterocycles from an Australian marine sponge, Trachycladus laevispirulifer. Org. Biomol. Chem. 2008, 6, 2765−2771. (11) Xiang, L.; Xing, D. M.; Wang, W.; Wang, R. F.; Ding, Y.; Du, L. J. Alkaloids from Portulaca oleracea L. Phytochemistry 2005, 66, 2595− 2601. (12) Gutierrez-Lugo, M. T.; Woldemichael, G. M.; Singh, M. P.; Suarez, P. A.; Maiese, W. M.; Montenegro, G.; Timmermann, B. N. Isolation of three new naturally occurring compounds from the culture of Micromonospora sp P1068. Nat. Prod. Res. 2005, 19, 645−652. (13) Huettner, J. E. Indole-2-Carboxylic Acid - a Competitive Antagonist of Potentiation by Glycine at the Nmda Receptor. Science 1989, 243, 1611−1613. (14) Liu, J. Q.; Qian, C.; Chen, X. Z. Syntheses of Indole-2-carboxylic Acid and Indoline-2-carboxylic Acid and Transformation from Each Other. Chin. J. Org. Chem. 2011, 31, 634−645. (15) Liu, J. Q.; Qian, C.; Chen, X. Z. Solubilities of 2,4-Dinitro-Lphenylalanine in Monosolvents at (273.15 to 368.15) K. J. Chem. Eng. Data 2010, 55, 5302−5304. 3313

dx.doi.org/10.1021/je400813d | J. Chem. Eng. Data 2013, 58, 3309−3313