Article pubs.acs.org/jced
Measurement and Correlation of the Solubilities of L‑Valine in Water, Ethanol, N,N‑Dimethylformamide, Acetone, and Isopropyl Alcohol between (293.15 and 343.15) K Chuntao Zhang,*,†,‡ Bangyu Liu,† Xin Wang,† and Hairong Wang‡ †
College of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan, Hubei 430081, China Hubei Province Key Laboratory of Coal Conversion and New Carbon Materials, Wuhan University of Science and Technology, Wuhan, Hubei 430081, China
‡
ABSTRACT: The solubilities of L-valine in water, ethanol, N,N-dimethylformamide, acetone, and isopropyl alcohol were experimentally measured by the synthetic method over the temperature range from (293.15 to 343.15) K at atmosphere pressure. The solubilities of L-valine in pure solvents increase with increasing temperature and in the following order: acetone < N,Ndimethylformamide < isopropyl alcohol < ethanol < water. The solubilities correlated using the modified Apelblat model show good agreement with the experimental data, and the dissolution enthalpy, dissolution entropy, and the molar Gibbs energy were predicted. The experimental solubilities and the modified Apelblat model can be used as essential data and model in the industrial manufacturing process of L-valine.
associating fluid theory (SAFT) equation.2 The solubility of Lvaline in water was measured at 298.15 K and pressures up to 400 MPa, and it was found that L-valine has a solubility maximum at around 100 MPa.3 Solid−liquid equilibria of Lleucine/L-valine/water were measured at 298 K and ambient pressure, and the results showed that the equilibrium concentration of L-valine increased significantly with the addition of L-leucine.4 Data on the solubilities of L-valine in pure ethanol, N,Ndimethylformamide, isopropyl alcohol, and acetone are relatively lacking. In this work, the solubilities of L-valine in five pure solvents (water, ethanol, N,N-dimethylformamide, isopropyl alcohol, and acetone) were measured by the laser monitoring observation technique. The use of this technique to determine solubility data is simple and time-saving. What is more important is that more and more published solubility data measured by this technique have proved to be reliable.5−9
1. INTRODUCTION Solubility is an important physicochemical property and has an especially broad application and great importance in a wide
Figure 1. Chemical structure of L-valine (CAS no. 72-18-4).
variety of industrial productions. As an essential amino acid, Lvaline (C5H11NO2, CAS no. 72-18-4) is widely used in the pharmaceutical, food, and feed industries and so on. The molecular structure of L-valine is given in Figure 1. L-Valine is mainly manufactured by fermentation together with a series of subsequent separation and purification operations, such as membrane separation and crystallization. In order to select a proper solvent system and to design an optimized separation process for the industrial production of L-valine, it is of great necessity to study the phase equilibrium behavior, especially the solubility data in different solvents as far as possible. Pradhan and Vera1 found that there was an effect of the counterion on the solubility of DL-valine at high concentrations of acids or bases and that the solubility of DL-valine was higher in nitric acid than in hydrochloric acid and higher in potassium hydroxide than in sodium hydroxide. The solubility of DLvaline in ethanol−water was been modeled using the statistical © 2014 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Chemicals. A white powder of L-valine was supplied by J&K Scientific Ltd. (Beijing, China) with a mass-fraction purity of 0.9940. The L-valine powder was ground in an agate mortar, then fractionated into the particle size range of (125 to 150) μm, and finally stored in a dehydrator. The ethanol, acetone, N,N-dimethylformamide, and isopropyl alcohol (purchased from Sinopharm Chemical Reagent Ltd., Shanghai, China) for Received: January 14, 2014 Accepted: July 30, 2014 Published: August 11, 2014 2704
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0.04960 0.09910 0.1983 0.2974 0.3965 − 293.15 302.95 313.35 323.35 328.15 − 0.3337 −0.05830 −2.250 3.549 −1.941 0.3000 293.45 303.05 313.35 323.25 333.05 343.35 −3.717 5.377 2.395 −3.663 −3.968 3.266
a
0.2704 0.1380 0.3262 0.1063 −0.1070 0.2536
293.15 303.75 313.15 323.15 333.25 343.25
1.178 2.357 3.692 5.342 7.620 10.92 0.8838 0.9381 1.011 1.086 1.172 1.291 293.55 303.05 313.15 323.05 333.25 343.15
The standard uncertainty for temperature is u(T) = 0.05 K, and the relative standard uncertainty for solubility is ur(x) = 0.005.
0.1246 0.2492 0.4361 0.7476 1.059 1.495 293.15 303.25 313.25 323.15 333.25 343.25 −1.825 3.788 −1.238 −1.355 −0.1516 0.6725
10 ·x T/K 10 ·RD 10 ·x
0.2561 0.4609 0.7170 1.076 1.537 2.100
105·x 10 ·RD
T/K
Figure 3. Mole-fraction solubilities of L-valine in different solvents between (293 and 343) K: ▲, ethanol; ◆, isopropyl alcohol; ★, N,Ndimethylformamide; ●, acetone. Solid lines are fits based on eq 2.
T/K
Figure 2. Mole-fraction solubility of L-valine in water as a function of temperature: ◆, Dalton and Schmidt;11 □, this work; ★, Kurosawa et al.;4 ○, Fasman.10 Solid lines are fits based on eq 2.
10 ·RD
doubly distilled
10 ·x
18.02
T/K
water
10 ·RD
0.995
10 ·x
58.08
T/K
acetone
acetone
0.995
2
73.09
5
N,Ndimethylformamide
N,N-dimethylformamide
0.997
2
60.10
5
isopropyl alcohol
isopropyl alcohol
0.997
2
46.07
5
ethanol
manufacturer J&K Scientific Ltd. (Beijing, China) Sinopharm Chemical Reagent Ltd. (Shanghai, China) Sinopharm Chemical Reagent Ltd. (Shanghai, China) Sinopharm Chemical Reagent Ltd. (Shanghai, China) Sinopharm Chemical Reagent Ltd. (Shanghai, China) our laboratory
ethanol
0.994
2
117.15
2
L-valine
water
massfraction purity
Table 2. Mole-Fraction Solubilities (x) of L-Valine in Pure Solvents from (293 to 343) K at P = 0.1 MPaa
compound
molecular weight
102·RD
Table 1. Details of the Materials Used
0.3741 −1.856 4.065 −5.494 2.783 −
Article
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Table 3. Values of the Parameters in Equation 2 for L-Valine in Pure Solvents solvent
a
water ethanol isopropyl alcohol N,N-dimethylformamide acetone
−78.68 359.2 257.6 416.2 473.2
b/K 2.830 −2.107 −1.621 −2.433 −2.720
× × × × ×
3
10 104 104 104 104
mA /MA mA /MA + mB /MB
105·σx
102·F
R2
11.32 −52.58 −37.88 −61.04 −69.53
6.701 0.2379 0.01283 0.01577 0.01069
0.4144 3.731 1.505 1.405 2.914
0.9973 0.9953 0.9988 0.9992 0.9960
Table 4. Molar Enthalpies ΔsolH°, Molar Entropies ΔsolS°, and Molar Gibbs Energies ΔsolG° of Dissolution of L-Valine in Different Solvents from (293.15 to 343.15) K
experiments were of analytical reagent grade with mass-fraction purities better than 0.995. In all of the experiments, doubly distilled water was used. More details about the purities and sources of the materials are listed in Table 1. All of the chemicals were used as received without further purification. 2.2. Apparatus and Procedure. The solubilities of Lvaline in water, ethanol, isopropyl alcohol, N,N-dimethylformamide, and acetone from (293.15 to 343.15) K were measured by the synthetic method described in detail in our previous work.9 A 150 mL jacketed glass vessel with a magnetic stirrer (model 85-2, Yichen Instrument, China) for continuous mixing was used in the experiment. The desired temperature in the vessel was maintained by water circulating from a thermostatic bath (model HC2010, Wanda/Sida Instrument, China) with an accuracy of ± 0.05 K. A condenser was used to prevent the solvent from evaporating. An analytical balance with an accuracy of ± 0.0001 g (model AB204-N, Mettler Toledo, Greifensee, Switzerland) was used to weigh the solvent and Lvaline. A laser monitoring system was employed to determine the dissolution of the L-valine in different solvents. All of the experiments were conducted three times. The mole-fraction solubilities (x) of L-valine in water, ethanol, isopropyl alcohol, N,N-dimethylformamide, and acetone from (293.15 to 343.15) K at atmospheric pressure were calculated using eq 1: x=
c
T K
ΔsolH° kJ·mol
ΔsolS°
−1
−1
J·mol ·K
ΔsolG° −1
kJ·mol−1
Water 293.55 303.05 313.15 323.05 333.25 343.15
−25.27 −22.27 −19.19 −16.26 −13.33 −10.57
4.099 4.993 5.943 6.875 7.835 8.767
11.52 11.74 11.95 12.13 12.28 12.40
Ethanol 293.15 303.75 313.15 323.15 333.25 343.25 293.45 303.05 313.35 323.25 333.05 343.35
(1) 293.15 303.25 313.25 323.15 333.25 343.25
where mA, MA, mB, and MB are the masses and molecular weights of the solute and solvent, respectively. The results are shown in Figures 2 and 3 and listed in Table 2.
3. RESULTS AND DISCUSSION 3.1. Solubility Data for L-Valine. So as to verify the reliability of the experimental procedure described above, the experimentally determined solubilities of L-valine in water were compared with the literature data,4,10,11 as shown in Figure 2. The measured solubilities of L-valine in water are in good agreement with the literature data except for those determined by Dalton and Schmidt11 in 1933. The data reported by Dalton and Schmidt were rather old and much higher than the subsequent literature values. The reason for this, as concluded by Kurosawa et al.,4 is that the sample used by Dalton and Schmidt was DL-valine, as the solubility of DL-valine in water is much greater than that of L-valine in water. As shown in Figures 2 and 3, the solubility of L-valine in each solvent increases with increasing temperature. Furthermore, Lvaline is slightly soluble in acetone, N,N-dimethylformamide, isopropyl alcohol, and ethanol, whereas it is very soluble in water. Hence, acetone, N,N-dimethylformamide, isopropyl alcohol, and ethanol can be used as antisolvents to design antisolvent crystallization (or diluent crystallization) methods for L-valine separation and purification, while water is a good solvent for L-valine.
293.15 302.95 313.35 323.35 328.15
47.03 42.39 38.28 33.91 29.50 25.12
65.93 50.40 37.08 23.33 9.880 −3.044 Isopropyl Alcohol 42.35 37.39 39.33 27.25 36.09 16.72 32.97 6.927 29.88 −2.479 26.67 −11.98 N,N-Dimethylformamide 53.51 69.93 48.38 52.74 43.31 36.27 38.29 20.48 33.16 4.865 28.08 −10.14 Acetone 56.68 72.27 51.01 53.26 45.00 33.74 39.22 15.58 36.45 7.067
27.70 27.08 26.67 26.37 26.20 26.17 31.38 31.07 30.84 30.73 30.71 30.78 33.01 32.39 31.95 31.67 31.54 31.57 35.49 34.88 34.43 34.18 34.13
The solubilities of L-valine in the above solvents increased in the order acetone < N,N-dimethylformamide < isopropyl alcohol < ethanol < water, which can be explained by the wellknown rule that “like dissolves like”. The solubility of L-valine also depends on the polarity of the solvent to some degree. The polarities of the solvents increase in the order isopropyl alcohol < ethanol < acetone < N,N-dimethylformamide < water,12 as do the solubilities determined by experiments (Table 2 and Figures 2 and 3), except for acetone and N,N-dimethylformamide. The polarities of N,N-dimethylformamide and acetone are stronger than those of ethanol and isopropyl alcohol, but the solubilities in N,N-dimethylformamide and acetone are lower than those in ethanol and isopropyl alcohol. The 2706
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Figure 4. Molar Gibbs energy of dissolution at (a) 293.15 K and (b) 323.15 K as a function of the solubility of L-valine in the five solvents: ■, water; ●, ethanol; ★, isopropyl alcohol; ▼, N,N-dimethylformamide; ◆, acetone.
where N is the number of experimental data points. The relative deviation (RD) is listed in Table 2. The values of σx, F, and the adjusted R2 are listed in Table 3. Figures 2 and 3 compare the experimental and calculated solubility data for L-valine in water, ethanol, isopropyl alcohol, N,N-dimethylformamide, and acetone from (293.15 to 343.15) K. It is indicated that the modified Apelblat model can correlate the experimental solubility data of L-valine in the above five solvents well. 3.3. Prediction of Molar Dissolution Enthalpy, Entropy, and Gibbs Energy. The molar enthalpies ΔsolH° (kJ·mol−1), entropies ΔsolS° (J·mol−1·K−1), and Gibbs energies ΔsolG° (kJ·mol−1) of dissolution of L-valine in the above five different solvents can be calculated using eqs 6 to 8, which were obtained from the modified van’t Hoff equation and the Apelblat model:16
abnormal solubility behavior may explained by the interaction between the solvent molecules and solute molecules.9,13 Ethanol and isopropyl alcohol can act as both hydrogen-bond donors and acceptors, allowing them to form hydrogen bonds to L-valine more easily, which may accelerate the dissolution process; in contrast, acetone and N,N-dimethylformamide can act only as hydrogen-bond acceptors. This may be the reason why the solubilities of L-valine in N,N-dimethylformamide and acetone are lower than those in ethanol and isopropyl alcohol. 3.2. Solubility Data Correlation. Solubility data can be correlated and predicted by many equations. However, in order to be more convenient and have high value for practical applications, simple mathematical expressions for solubility equations are needed.14 Hence, the temperature dependence of the solubilities of L-valine in the five pure solvents was correlated by the modified Apelblat model as follows:15 b + c ln(T ) T
ln(x) = a +
⎡ ∂ ln(x) ⎤ Δsol H ° = RT ⎢ ⎥ = R( −b + cT ) ⎣ ∂ ln(T ) ⎦
(2)
⎡ ∂ ln(x) ⎤ + ln(x)⎥ = R {a + c[1 + ln(T )]} Δsol S° = R ⎢ ⎣ ∂ ln(T ) ⎦
where x is the mole fraction solubility; a, b, and c are constants characteristic of the solvent; and T is the absolute temperature. According to nonlinear least-squares regression, the experimental solubility data were fitted to eq 2. The values of a, b, and c are listed in Table 3. The relative deviation (RD) between the experimental and calculated values is defined as follows: RD =
x exp − x cal x exp
(7)
Δsol G° = Δsol H ° − T Δsol S°
(4)
(5)
4. CONCLUSIONS The solubilities of L-valine in the pure solvents water, ethanol, isopropyl alcohol, N,N-dimethylformamide, and acetone were
(3)
F=
1 N
N
∑ i=1
⎤1/2
N
∑
(xiexp
−
i=1
xiexp − xical xiexp
xical)2 ⎥ ⎥⎦
(8)
where R is the gas constant, T is the absolute temperature, x is the mole-fraction solubility, and a, b and c are the constants in eq 2. The thermodynamic functions ΔsolH°, ΔsolS°, and ΔsolG° were calculated, and the results are listed in Table 4. The dissolution process of L-valine in each solvent is endothermic, as each value of ΔsolH° in Table 4 is greater than 0. Moreover, ΔsolH° increases with increasing temperature for the dissolution of L-valine in water but decreases for the other solvents. Good linear correlations between the molar Gibbs energies of dissolution of L-valine in the five solvents and ln(x) at (293.15 and 323.15) K can be observed in Figure 4, which shows that lower values of ΔsolG° correspond to a more favorable process of dissolution and to higher solubilities.
where xexp and xcal i i represent the experimental and calculated solubility values, respectively. The root-mean-square deviation (RMSD, σx) and the objective function value (F) of the mole fraction are expressed as follows: ⎡ 1 σx = ⎢ ⎢⎣ N − 1
(6)
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(13) Hu, Y. H.; Jiang, X. M.; Yang, W. G.; Chen, Z. G.; Meng, X. Q.; Shen, F. Solubility of erythritol in different aqueous solvent mixtures. J. Mol. Liq. 2012, 169, 74−79. (14) Mullin, J. W. Crystallization, 3rd ed.; Butterworth Heinemann: Oxford, U.K., 1997. (15) 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. (16) Sousa, J. M. M. V.; Almeida, J. P. B.; Ferreira, A. G. M.; Fachada, H. C.; Fonseca, I. M. A. Solubility of HFCs in lower alcohols. Fluid Phase Equilib. 2011, 303, 115−119.
experimentally measured by the synthetic method at temperatures ranging from (293.15 to 343.15) K at atmospheric pressure. The experimental data indicated that the solubility of L-valine increases in the order acetone < N,N-dimethylformamide < isopropyl alcohol < ethanol < water. Acetone, N,Ndimethylformamide, isopropyl alcohol, and ethanol can be used as antisolvents to design antisolvent crystallization (or diluent crystallization) methods for the separation and purification of Lvaline, while water is a good solvent for L-valine. The solubilities calculated by the modified Apelblat model show good agreement with the experimental data, and hence, the experimental solubilities and the modified Apelblat model can be used as essential data and model in the industrial manufacturing process of L-valine.
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AUTHOR INFORMATION
Corresponding Author
*Tel: 86-27-86559634. Fax: 86-27-86559634. E-mail:
[email protected]. Funding
Financial support from the National College Students’ Innovation and Entrepreneurship Training Program (201210488002) and the Open Foundation of Hubei Province Key Laboratory of Coal Conversion and New Carbon Materials (WKDM201106) is gratefully acknowledged. Notes
The authors declare no competing financial interest.
■
REFERENCES
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