Measurement and Correlation of Solubility of l-Valine in Water +

Article pubs.acs.org/jced

Measurement and Correlation of Solubility of L‑Valine in Water + (Ethanol, N,N-Dimethylformamide, Acetone, Isopropyl Alcohol) from 293.15 K to 343.15 K Chuntao Zhang,*,† Bangyu Liu,† Xin Wang,† Hairong Wang,† and Haitao Zhang†,‡ †

College of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081, Hubei Province China ‡ Sunovion Pharmaceuticals Inc., 84 Waterford Drive, Marlborough, Massachusetts 01581, United States ABSTRACT: The solubilities of L-valine in four binary mixed solvents of water + (ethanol, isopropyl alcohol, N,N-dimethylformamide, acetone) were experimentally measured from 293.15 K to 343.15 K at atmospheric pressure by employing the synthetic method. The experimental data indicate that the solubility of L-valine in the binary mixed solvents increases with the increasing temperature and decreases with the rise of mass concentration (w) of nonaqueous solvent in the binary aqueous solution. The experimental data can be correlated by using the modified Apelblat model, λh model, and CNIBS/R-K model. The results indicate that the solubility data show agreement with the modified Apelblat model much better than others in the studied binary solvents system. The dissolution enthalpy, dissolution entropy, and molar Gibbs energy of the dissolution of L-valine in the studied binary mixed solvents were then calculated. The experimental data and the correlation equations in this work can be used as essential data and models in the industrial manufacture process of L-valine, especially in antisolvent crystallization. water,4 which indicates that the solubility of DL-valine cannot be applied to L-valine directly. To select a proper solvent system and to design an optimized separation process for the industrial crystallization of L-valine, it is necessary to study as far as possible the phase equilibrium behavior, especially the solubility data in the binary mixed solvents. At present, more and more attention has been paid to the solubility prediction, which is of great importance in industrial applications. Lots of methods and thermodynamic models have been used to estimate and correlate the solubility, but related research on the solubility prediction of L-valine in the above binary mixed solvents has been still unavailable. In this work, the solubility of L-valine in different binary mixed solvents of water + (ethanol, N,N-dimethylformamide, acetone, isopropyl alcohol) was experimentally measured from 293.15 K to 343.15 K at atmospheric pressure by using the synthetic method, which is reliable, simple, timesaving, and has been used extensively.5−7 The modified Apelblat model, the λh model, and the (CNIBS/R-K) model were employed to correlate the experimental data.

1. INTRODUCTION L-Valine (CAS No. 72-18-4), C5H11NO2, is an essential amino acid and has been 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

Figure 1. Chemical structure of L-valine (CAS No. 72-18-4).

fermentation together with a series of subsequent separation and purification operations, such as membrane separation and crystallization. Our previous study indicated that L-valine is very soluble in water but slightly soluble in acetone, N,N-dimethylformamide, isopropyl alcohol, and ethanol, which suggests that an antisolvent crystallization for L-valine separation and purification may be a more proper choice. However, the solubility of L-valine in binary mixed solvents of water + (ethanol, N,N-dimethylformamide, acetone, isopropyl alcohol) has been still unavailable, except for the solubility in water which can be found in the literature.1−4 The solubility of DLvaline in (ethanol−water) had been modeled by the statistical associating fluid theory (SAFT) equation,2 but the solubility of DL-valine in water is much greater than that of L-valine in © 2014 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials. A white powder of L-valine was supplied by J&K Scientific Ltd. (Beijing, China) with a purity of 99.40 %. Received: March 16, 2014 Accepted: July 30, 2014 Published: August 11, 2014 2732

dx.doi.org/10.1021/je500255d | J. Chem. Eng. Data 2014, 59, 2732−2740

Journal of Chemical & Engineering Data

Article

Table 1. Details of the Materials Used compound

molecular weight

mass fraction purity

117.15 46.07 60.1 73.09 58.08 18.02

0.994 0.997 0.997 0.995 0.995 double distilled water

L-valine

ethanol isopropyl alcohol N,N-dimethylformamide acetone water

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 experiments are of analytical reagent grade and their mass fraction purities are not less than 0.995. In all experiments double-ionized water was used. More details about the purity and source of the materials are listed in Table 1. All chemicals were used received without further purification. 2.2. Apparatus and Procedure. The solubility of L-valine in four different binary mixed solvents of water + (ethanol, N,N-dimethylformamide, acetone, isopropyl alcohol) was experimentally measured from 293.15 K to 343.15 K at atmospheric pressure by using the synthetic method described in our previous work in detail.8 A 150 mL jacketed glass vessel with a magnetic stirrer (Yichen Instrument 85-2, China) for continuous mixing was used in the experiment. The desired temperature in the vessel was maintained by water circulating from a thermostatic bath (Wanda/Sida Instrument HC2010, China) with an accuracy of ± 0.05 K. A condenser was used to prevent the solvent from evaporating. An analytical balance (Metler Toledo AB204-N, Switzerland) with an accuracy of ± 0.0001 g was used to measure the solvent and L-valine. A laser monitoring system was employed to determine the dissolution of the L-valine in different solvents. All the experiments were conducted three times. The mole fraction solubility (x) of L-valine in the binary mixed solvents was calculated by using eq 1, and the initial mass fraction concentration (w) of the binary solvent mixtures is defined by eq 2.

manufacturer J&K Scientific Ltd. Beijing, China Sinopharm Chemical Reagent Ltd., Sinopharm Chemical Reagent Ltd., Sinopharm Chemical Reagent Ltd., Sinopharm Chemical Reagent Ltd., our laboratory

Shanghai, Shanghai, Shanghai, Shanghai,

China China China China

Figure 2. Mole fraction solubility of L-valine in water: ◆, Dalton and Schmidt;14 □, this work; ★, Izumi Kurosawa;4 ○, Fasman.13 Solid line, calculated from eq 3.

x=

mA /MA mA /MA + mB /MB + mC /MC

(1)

where x is the mole fraction solubility, T is the absolute temperature, a, b, and c are empirical constants. The constants a and b represent the variation in the solution activity coefficient and provide an indication of the influence of nonideal solution on the solubility of solute; while the constant c reflects the effect of temperature on the fusion enthalpy.9 2.3.2. The λh Model. The λh model10 is another more convenient semiempirical model and has numerous practical applications in solubility correlation and prediction in mixed solvents. Plenty of experimental solubility data experimentally measured has been well correlated by the λh model with only two model parameters of λ and h, which can be described as follows:

w=

mC mB + mC

(2)

(4)

⎛1 ⎡ λ(1 − x) ⎤ 1 ⎞ ln⎢1 + ⎟ ⎥ = λh⎜ − ⎣ ⎦ x Tm ⎠ ⎝T

where x is the mole fraction solubility, λ and h are the model parameters that can be fitted from the experimental solubility data, T is the absolute temperature, and Tm is the absolute melting temperature of the solute. 2.3.3. The Combined Nearly Ideal Binary Solvent/Redlich− Kister (CNIBS/R-K) Model. The CNIBS/R-K model11 is a famous and widely used solid−liquid equilibrium model that can accurately describe how the experimental isothermal solubility of a crystalline solute dissolved in binary solvent mixtures varies with binary solvent composition altering, which can be described as follows:

where m is the mass and M is the molecular weight, while the subscripts of A, B, and C represent solute (L-valine), water, and solvent (ethanol, N,N-dimethylformamide, acetone, or isopropyl alcohol), respectively. 2.3. Solubility Data Correlation. To find more reliable and practical thermodynamic models, three typical thermodynamic models were applied and compared to correlate and predict the solubility data of L-valine in this work. 2.3.1. The Modified Apelblat Model. As one of the commonly and widely used models in solubility correlation and prediction based on the nonideal solution, the modified Apelblat model9 has a very simple mathematical expression and can be expressed as follows: b ln(x) = a + + c ln(T ) T

2

3

4

ln x = B0 + B1xC0 + B2 xC0 + B3xC0 + B4 xC0

(5)

where x is the mole fraction solubility of solute defined as eq 1; B0, B1, B2, B3, and B4 are the model parameters; x0C refers to the initial mole fraction concentration of the binary solvent

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Table 2. Mole Fraction Solubility of L-Valine in Ethanol (w) + Water (1 − w) from from 293.15 K to 343.15 K at Atmosphere Pressurea 102RD 3

T/K

a

10 x

293.35 303.35 313.15 323.05 332.95 343.25

0.1781 0.2134 0.3059 0.3841 0.5009 0.6483

293.15 303.05 313.05 323.15 333.25 343.05

0.1614 0.1918 0.2427 0.3085 0.3810 0.4730

293.15 303.25 313.15 323.25 333.05 343.05

0.4238 0.4874 0.5424 0.6105 0.6781 0.7350

eq 3 100 w = 89.98 2.409 −2.240 2.713 0.1833 0.5319 −0.8070 100 w = 50.03 1.159 −2.200 −0.2190 1.692 0.1280 −0.6190 100 w = 10.12 −0.8225 0.4965 −0.7670 −0.1177 0.6964 −0.3456

eq 4

102RD T/K

eq 5

2

10 x

2.870 −2.772 2.263 1.408 2.768 5.011

0.1806 0.1136 0.4594 0.6539 0.7642 1.095

293.35 303.05 312.95 323.05 333.25 343.05

0.07544 0.08949 0.1110 0.1391 0.1754 0.2136

2.281 −3.800 −2.597 0.2695 1.079 3.810

1.212 0.7594 3.054 4.319 5.028 2.377

293.15 303.15 313.25 323.15 333.05 343.05

0.2797 0.3275 0.3839 0.4538 0.5267 0.5985

−0.9011 1.046 0.2982 0.7747 0.5308 −2.181

0.3769 0.2359 0.9560 1.358 1.586 2.268

eq 3 100 w = 70.00 0.8749 −1.407 0.9296 0.5677 1.3122 −0.9728 100 w = 30.00 0.4438 −0.4738 −0.8808 0.6754 0.8826 −0.6789

eq 4

eq 5

2.018 −2.912 −2.591 1.380 2.834 4.318

−0.6310 −0.3930 −1.611 −2.301 −2.693 −3.889

1.052 2.255 −3.219 −2.079 −2.290 −4.348

−1.116 −0.6950 −2.861 −4.098 −4.804 −4.849

Standard uncertainities u are u(T) = 0.05 K, u(x) = 0.05x.

Table 3. Mole Fraction Solubility of L-Valine in Isopropyl Alcohol (w) + Water (1 − w) from 293.15 K to 343.15 K at Atmosphere Pressurea 102RD 3

T/K

a

10 x

293.25 303.25 313.05 323.25 332.95 343.15

0.09963 0.1577 0.2408 0.4566 0.7555 1.137

293.25 303.35 313.15 323.15 333.05 343.05

0.02340 0.05620 0.1026 0.1788 0.2656 0.3761

293.15 303.35 313.15 323.05 333.15 343.25

0.0784 0.1287 0.1939 0.2675 0.3579 0.4701

eq 3 100 w = 89.97 2.350 −1.120 −2.716 4.764 3.150 −4.667 100 w = 49.97 −1.667 −2.992 −1.617 0.4958 −1.879 1.263 100 w = 9.997 −0.5680 0.4335 1.439 −0.879 −1.487 1.031

eq 4 1.501 −3.826 −1.684 4.604 4.684 −4.792 −0.914 2.537 −1.527 −0.7460 0.3806 1.490 −1.497 3.575 4.553 −1.132 4.517 −3.322

102RD T/K

eq 5 2.433 0.7993 0.7641 1.202 1.090 0.8937 −3.757 2.198 3.742 3.812 2.537 2.285

2

10 x

293.15 303.35 313.15 323.05 333.05 343.15

0.08674 0.1819 0.3198 0.5010 0.7579 1.099

293.35 303.35 313.15 323.05 333.05 343.25

0.03980 0.0775 0.1334 0.1995 0.2946 0.4259

eq 3 100 w = 69.97 −1.562 2.301 1.561 −2.247 −1.754 1.606 100 w = 30.02 −1.527 1.709 2.719 −2.638 −2.331 1.931

eq 4

eq 5

−1.216 2.991 2.7016 −5.141 −2.431 −4.321

−2.258 −3.953 −3.775 −4.957 −5.424 −4.430

−1.321 5.256 4.398 −3.396 −2.596 −2.303

4.385 3.363 −4.242 4.341 −3.100 −3.778

2.035 3.506 3.353 5.232 4.748 3.911


calculated as if solute was not present, which can be defined as follows: xC0

=

The relative deviation (RD) between the experimental value (xexp) and the calculated value (xcal) is defined as follows:

mC MC mB MB

+

mC MC

RD =

(6) 2734

x exp − x cal x exp

(7)



Article

Table 4. Mole Fraction Solubility of L-Valine in N,N-Dimethylformamide (w) + Water (1 − w) from 293.15 K to 343.15 K at Atmosphere Pressurea 102RD T/K

3

10 x

eq 3

eq 4

102RD 2

T/K

eq 5

10 x

100 w = 89.89

a

293.25 303.25 313.05 322.95 333.25 343.05

0.09506 0.1331 0.1806 0.2472 0.3707 0.5513

293.15 303.35 313.25 323.05 333.35 343.25

0.06261 0.1503 0.2563 0.4169 0.6474 1.064

293.25 303.25 313.25 323.05 333.05 343.25

0.04940 0.08166 0.1219 0.1724 0.2347 0.3124

−1.435 2.401 0.9351 −2.524 −0.3810 0.9317 100 w = 50.01 1.803 2.468 0.6728 −3.305 −3.464 4.857 100 w = 10.03 −0.8490 1.5468 −0.2851 −0.6291 −0.832 0.7073

eq 3

eq 4

eq 5

−0.6722 2.302 −0.6045 4.199 −4.176 −4.670

4.116 −1.789 −2.753 −2.875 −4.213 −3.347

1.186 −4.078 −0.1580 3.819 4.281 1.741

2.124 −4.536 1.660 −4.799 −2.685 −4.378

100 w = 69.98 1.184 −1.283 −4.039 −4.284 5.213 2.214

−0.8460 0.2872 0.4399 0.4585 0.6665 1.014

293.25 303.25 313.05 323.35 333.25 343.35

0.2013 0.3376 0.5128 0.8375 1.104 1.596

−1.261 1.164 −1.473 −1.647 −3.895 −4.761

−4.199 4.698 −2.665 −2.338 2.171 −2.975

293.25 303.25 313.35 323.15 333.05 343.15

0.26.48 0.3873 0.6057 0.9154 1.311 1.797

−1.486 4.165 2.567 −1.156 −7.427 −0.1503

0.044 0.4634 −2.568 4.495 −3.630 0.9877 100 w = 29.99 2.136 −3.835 −0.7837 2.326 1.829 −1.835

3.627 2.127 3.239 3.377 4.879 3.562


Table 5. Mole Fraction Solubility of L-Valine in Acetone (w) + Water (1 − w) from 293.15 K to 343.15 K at Atmosphere Pressurea 102RD T/K

a

103x

293.35 303.35 313.25 323.25 333.15

0.1619 0.2428 0.3642 0.5666 0.7689

293.35 303.15 313.05 323.05 333.25

0.1618 0.2063 0.2744 0.3611 0.4784

293.15 303.15 313.25 323.35 333.15

0.1390 0.2013 0.3161 0.4458 0.5957

eq 3 100 w = 89.95 1.020 −1.672 −1.559 3.893 −1.814 100 w = 49.97 0.4329 −1.083 0.5773 0.3544 −0.2810 100 w = 10.03 1.531 −4.006 2.195 1.194 −1.053

eq 4

102RD 102x

T/K

eq 5

2.869 −1.896 −1.259 4.916 1.009

0.4534 −0.9540 −1.753 −2.293 −0.7977

293.15 303.25 313.15 323.25 333.15

0.3567 0.6537 1.129 1.694 2.674

1.248 −2.710 −1.072 0.7792 4.073

4.625 2.088 3.832 −3.684 −2.302

293.15 303.25 313.25 323.15 333.15

0.05190 0.08423 0.1295 0.1907 0.2720

−3.082 −4.278 −5.223 −4.846 −4.313

1.757 −3.774 3.173 −3.920 −3.148

eq 3 100 w = 69.99 −0.4249 1.047 2.587 −3.791 1.472 100 w = 30.03 −0.04705 0.1059 −0.04273 −0.06372 0.03747

eq 4

eq 5

−0.5420 1.962 3.268 −4.599 −2.026

−2.088 4.223 −2.130 4.213 3.546

−0.3688 1.167 0.7382 −1.006 −4.009

−4.941 4.588 −2.610 4.926 −3.120


The root-mean-square deviation (RMSD) and the relative average deviation (RAD) are described as follows: ⎡ 1 RMSD = ⎢ ⎢⎣ N − 1

N

∑ (xiexp i=1

⎤1/2 cal 2 ⎥ − xi ) ⎥⎦

RAD =

1 N

N

∑ i=1

xiexp − xical xiexp

(9)

Where N is the number of experimental data points, while xexp i and xcal represent the experimental and calculated solubility i values, respectively.

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Figure 5. Mole fraction solubility of L-valine in binary N,Ndimethylformamide (w)−water (1 − w) from 293.15 K to 343.15 K: ■, 100 w = 89.89; ●, 100 w = 69.98; ★, 100 w = 50.01; ◆, 100 w = 29.99; ▲, 100 w = 10.03. Solid line, calculated from eq 3.

Figure 3. Mole fraction solubility of L-valine in binary ethanol (w)− water (1 − w) from 293.15 K to 343.15 K: ■, 100 w = 89.98; ●, 100 w = 70.00; ★, 100 w = 50.03; ◆, 100 w = 30.00; ▲, 100 w = 10.12. Solid line, calculated from eq 3.

Figure 4. Mole fraction solubility of L-valine in binary isopropyl alcohol (w)−water (1− w) from 293.15 K to 343.15 K: ■, 100 w = 89.97; ●, 100 w = 69.97; ★, 100 w = 49.97; ◆, 100 w = 30.02; ▲, 100 w = 9.997. Solid line, calculated from eq 3.

Figure 6. Mole fraction solubility of L-valine in binary acetone (w)− water (1 − w) from 293.15 K to 343.15 K: ■, 100 w = 89.95; ●, 100 w = 69.99; ★, 100 w = 49.97; ◆, 100 w = 30.03; ▲, 100 w = 10.03. Solid line, calculated from eq 3.

2.4. Prediction of Dissolution Enthalpy, Entropy, and the Molar Gibbs Energy. The dissolution enthalpy ΔsolHo (kJ·mol−1), dissolution entropy ΔsolSo (J·mol−1·K−1), and molar Gibbs energy ΔsolGo (kJ·mol−1) of a solution of Lvaline in the above different mixed solvents can be calculated by using eqs 10 to 12, which are obtained by the modified van’t Hoff equation and the Apelblat model.12 ⎡ ∂ ln x ⎤ Δsol H ο = RT ⎢ = R( −b + cT ) ⎣ ∂ ln T ⎥⎦

(10)

⎡ ∂ ln x ⎤ Δsol S ο = RT ⎢ + ln x ⎥ = R[a + c(1 + ln T )] ⎣ ∂ ln T ⎦ (11) ο

ο

Δsol G = Δsol H − T Δsol S

ο

(12)

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 of eq 3.

Figure 7. Comparisons with the mole fraction solubility of L-valine in ethanol−water mixed solvents. 2736



Article

The experimentally measured solubility of L-valine in four binary mixed solvents of water + (ethanol, N,N-dimethylformamide, acetone, isopropyl alcohol) from 293.15 K to 343.15 K at atmospheric pressure by using the synthetic method is listed in Tables 2 to 5 and shown in Figures 3 to 6, which indicated that the solubility of L-valine in each binary mixed solvent increases with the increasing temperature while it decreases with the rise of mass concentration (w) of solvent (ethanol, isopropyl alcohol, or N,N-dimethylformamide, acetone) in the binary aqueous solution, but the variation trend of which in each mixed solvent is different. Hence, acetone, N,N-dimethylformamide, isopropyl alcohol, and ethanol can be used as antisolvents to design antisolvent crystallization for L-valine separation and purification, while water is a good solvent for L-valine. Furthermore, for a fixed water ratio, the solubility of L-valine in the above binary solutions increases in the order: water + acetone < water + N,N-dimethylformamide < water + isopropyl alcohol < water + ethanol. The phenomenon can be explained by the well-known rule called “like dissolves like”. As shown in Figure 1, there are a carboxyl group and an amino group in the molecule of L-valine, which are both strong polar groups. The polarity of the studied solvents is in the order isopropyl alcohol < ethanol < acetone < N,N-dimethylformamide < water,15 so are the solubility values as determined by experiments (Tables 2 to 5 and Figures 3 to 6) when the water concentration is the same, except for that of water + acetone and water + N,N-dimethylformamide. The polarity of N,N-dimethylformamide and acetone are stronger than that of ethanol and isopropyl alcohol, but the solubility in N,N-dimethylformamide and acetone is lower than that in ethanol and isopropyl alcohol. The abnormal solubility behavior may be explained by the interaction between solvent molecules and solute molecules. Ethanol and isopropyl alcohol can act as both hydrogen-bond donor and acceptor which allows

Figure 8. Comparisons with the mole fraction solubility of DL-valine in ethanol−water mixed solvents.

3. RESULTS AND DISCUSSION 3.1. Solubility Data of L-Valine. So as to verify the reliability of the experimental procedure described above, the experimentally determined solubility of L-valine in water was compared with the literature data,4,13,14 as shown in Figure 2. The measured solubility of L-valine in water is in good agreement with that determined by Izumi Kurosawa4 and Fasman,13 but not that determined by Dalton and Schmidt14 in 1933. The data reported by Dalton and Schmidt were rather old and much higher than the subsequent literature values. The proper reason, concluded by Izumi Kurosawa, was that the sample used by Dalton and Schmidt was DL-valine because the solubility of DL-valine in water is much greater than that of L-valine in water.

Table 6. Parameters of the Modified Apelblat Model for L-Valine in Binary Mixed Solvents from 293.15 K to 343.15 K 100 w

a

89.98 70.00 50.03 30.00 10.12

−108.1111 −133.5126 −125.2566 −24.4984 22.3009

89.97 69.97 49.97 30.02 9.997

−230.5649 397.1364 628.9090 348.4508 246.8606

89.89 69.98 50.01 29.99 10.03

−309.1120 154.0508 344.6470 −7.2041 212.1995

89.95 69.99 49.97 30.03 10.03

−23.1925 204.3193 −157.6961 102.5072 81.3923

b

c

Ethanol 2417.1039 16.0550 4118.2371 19.7621 3716.0358 18.6843 −435.12615 3.5381 −2237.7437 −3.5437 Isopropyl Alcohol 6021.6853 34.9392 −23285.2447 −57.5709 −34526.6208 −91.4474 −20663.2346 −50.3096 −14899.3345 −35.7670 N,N-Dimethylformamide 11000.6231 45.7751 −11209.5880 −22.2916 −21215.2055 −49.6253 −3360.4244 1.8316 −13395.9116 −30.6500 Acetone −2824.3877 3.4281 −14142.6190 −29.6823 4541.0098 23.0896 −8606.3770 −14.6135 −7225.6010 −11.5551 2737

105 RMSD

102 RAD

0.5387 1.633 3.396 3.547 3.594

1.481 1.011 1.003 0.6726 0.5410

0.2796 1.148 3.287 5.617 3.620

3.128 1.839 1.652 2.142 0.9728

0.04060 0.2630 1.514 2.187 1.534

1.435 2.031 2.279 2.124 0.8084

0.01350 0.04054 0.01691 0.009587 0.68081

1.992 1.865 0.5457 0.05937 1.996



Article

Table 7. Parameters of the λh Model for L-Valine in Binary Mixed Solvents from 293.15 K to 343.15 K 100 w 89.98 70.00 50.03 30.00 10.12 89.97 69.97 49.97 30.02 9.997 89.89 69.98 50.01 29.99 10.03 89.95 69.99 49.97 30.03 10.03

λ

105 RMSD

h

Ethanol 206911.9 99556.56 41349.58 49770.84 65998.17 Isopropyl Alcohol 0.023584 193034.7 1.818744 3193.356 29.12904 235.2808 3.760671 1422.424 0.599520 6457.799 N,N-Dimethylformamide 0.002208 1447330 0.033265 130158.8 3.936853 1638.215 0.184584 20781.63 0.435318 9090.689 Acetone 0.001101 3469918 0.022569 226500.9 0.001178 2143259 0.060315 68356.13 0.051703 65479.46 0.012038 0.019430 0.048990 0.028108 0.011572

water + N,N-dimethylformamide and water + acetone are lower than water + ethanol and water + isopropyl alcohol for a fixed water ratio. The solubility diagrams of L-valine in binary mixed solvents ethanol−water at 303.15 K were established by Hamedi and Grolier16 via isothermal titration calorimetry (ITC). The values are greatly different from what we have found in experiments, as seen in Figure 7. In our experiments, the solubility of L-valine decreases with the increasing ethanol weight fraction in the mixed solvent at a constant temperature, while the SLE data determined by Hamedi indicated that the solubility of L-valine in pure ethanol is higher than that in pure water, and the variation trend of the solubility of L-valine increases with the increasing ethanol weight fraction. These findings disagreed with others that the solubility of amino acids in pure alcohol can be much lower than in pure water.2 The solubility of DL-valine in ethanol−water at 303.15 K established by Hamedi and Grolier16 via ITC was greatly different from that by Dunn and Ross,17 as shown in Figure 8. 3.2. Solubility Data Correlation. The experimentally measured solubility of L-valine in the binary mixed solvents was correlated by the modified Apelblat model, λh model, and CNIBS/R-K model, as listed in Tables 2 to 5, which indicated that the experimental solubility data show good agreement with the calculated data by using eq 3 to 5 according to the RDs. Together with the RMSDs and the RADs according to eq 3 to 5, the model parameters of the modified Apelblat model, λh model, and CNIBS/R-K model are listed in Tables 6 to 8, respectively. Moreover, compared with the λh model and CNIBS/R-K model, the RMSDs of the modified Apelblat model are smaller, which indicates that the modified Apelblat model regresses the solubility data much better in the studied

102 RAD

1.665 5.116 9.473 9.490 8.191

2.849 2.676 2.306 2.541 0.9553

2.444 2.430 2.784 7.099 8.410

3.462 3.191 1.266 3.212 3.100

0.1180 0.4242 1.595 3.350 5.528

3.036 2.771 2.128 2.544 2.563

0.01500 0.05132 0.1039 0.5579 1.931

2.390 2.479 1.976 1.458 4.348

them to more easily form hydrogen bonds with L-valine, which then may accelerate the dissolution process, while acetone and N,N-dimethylformamide can act only as hydrogen-bond acceptor. That may be the reason why the solubility of L-valine in

Table 8. Parameters of the CNIBS/R-K Model for L-Valine in Binary Mixed Solvents from 293.15 K to 343.15 K T/K

B0

B1

293.15 303.15 313.15 323.15 333.15 343.15

−5.3246 −5.1803 −5.1383 −5.0594 −4.9834 −4.9555

−3.1373 −3.2962 −1.7217 −0.8252 −0.1588 1.0467

293.15 303.15 313.15 323.15 333.15 343.15

−6.8733 −6.5223 −6.1842 −5.9856 −5.7415 −5.5011

−9.9123 −5.5088 −2.9964 0.6673 2.5033 3.9518

293.15 303.15 313.15 323.15 333.15 343.15

−7.2190 −6.9004 −6.5635 −6.2515 −6.0329 −5.8457

−12.3380 −8.2499 −6.0738 −4.7870 −1.5949 1.4280

293.15 303.15 313.15 323.15 333.15

−8.5537 −8.0421 −7.4502 −7.0618 −7.0060

−10.0274 −13.1288 −17.0021 −17.8259 −11.8888

B2

B3

Water−Ethanol −6.6534 16.8056 −4.3238 10.7654 −9.5943 18.1860 −10.9817 18.2095 −11.7676 18.2053 −14.7370 21.2470 Water−Isopropyl alcohol 21.4997 −36.9638 9.2031 −26.1670 1.7345 −18.6084 −13.1424 4.6972 −20.3056 16.0565 −25.8609 24.5041 Water−N,N-Dimethylformamide −2.6380 34.1807 −16.6845 49.2117 −25.1689 59.2791 −27.0482 57.5188 −43.1249 83.9422 −55.0732 101.1436 Water−Acetone −10.3316 37.5761 6.3718 9.7584 24.8224 −19.5269 28.0538 −23.1700 7.5331 3.6981 2738

B4

105 RMD

102 RAD

−12.9741 −8.6206 −11.9374 −11.1792 −10.7759 −11.7211

1.808 1.323 6.414 9.218 5.255 8.333

0.5930 0.3705 1.508 2.147 2.508 2.454

19.3753 16.7090 14.2102 2.3256 −3.5942 −7.8634

1.131 2.417 4.254 8.043 9.321 8.444

2.491 2.327 2.668 3.293 2.848 2.576

−25.5824 −30.2790 −33.8151 −31.2353 −44.6442 −52.7621

8.487 1.149 1.849 3.292 5.398 6.261

2.505 2.246 1.803 2.318 2.451 2.569

−23.1801 −8.7852 6.0228 7.2746 −5.4757

0.1619 0.3819 0.4758 0.8898 0.9235

2.323 2.631 2.297 3.235 5.816



Article

Table 9. Molar Gibbs Energy ΔsolGo, Molar Enthalpy ΔsolHo, and Molar Entropy ΔsolSo of L-Valine in Binary Mixed Solvents at 333.15 K ΔsolHo 100 w

kJ·mol

ΔsolSo

−1

−1

J·mol ·K

mixed solvents with the solubility (ln x) can be observed from Figure 9, which shows that lower values of ΔsolGo correspond to a more favorable process of dissolution and to an higher solubility.

ΔsolGo −1

kJ·mol−1

4. CONCLUSIONS The solubility of L-valine in four binary mixed solvents of water + (ethanol, N,N-dimethylformamide, acetone, isopropyl alcohol) was experimentally measured by the synthetic method from 293.15 K to 343.15 K at atmosphere pressure. The experimental data indicated that the solubility of L-valine in each binary mixed solvent increases with the increasing temperature while it decreases with the ris of mass concentration (w) of solvent (ethanol, N,N-dimethylformamide, acetone, or isopropyl alcohol). The experimental solubility data show good agreement with the modified Apelblat model, λh model, and CNIBS/R-K model, while the RMSDs of the modified Apelblat model are smaller and may regress the solubility data much better in the studied binary mixed solvents as a function of temperature. The thermodynamic functions of ΔsolHo, ΔsolSo, and ΔsolGo of Lvaline can be calculated and studied by using the Apelblat model. The experimental solubilities and correlation equations in this work can be used as essential data and models in the industrial manufacture process of L-valine, especially in antisolvent crystallization.

Ethanol 89.98 70.00 50.03 30.00 10.12 89.97 69.97 49.97 30.02 9.997 89.89 69.98 50.01 29.99 10.03 89.95 69.99 49.97 30.03 10.03

24.35 9.901 20.51 8.690 20.87 16.32 13.41 −3.408 8.792 −15.18 Isopropyl Alcohol 46.65 60.70 34.18 43.04 33.84 52.45 32.49 49.29 24.81 27.75 N,N-Dimethylformamide 35.37 21.34 31.43 18.87 38.85 56.03 33.01 43.78 26.50 29.31 Acetone 32.98 1.232 35.37 18.50 26.22 −4.006 31.08 25.02 28.07 22.60

21.05 17.62 15.43 14.55 13.85 26.44 19.85 16.37 16.07 15.56 28.26 25.15 20.17 18.43 16.74

■

32.57 29.21 27.55 22.74 20.54

AUTHOR INFORMATION

Corresponding Author

*Tel: 86-27-86559634. Fax: 86-27-86559634. E-mail: [email protected]. Permanent Address: Wuhan University of Science and Technology, Heping Road 947#, Qingshan District, Wuhan, 430081, China. Funding

Financial support from National College Students’ Innovation and Entrepreneurship Training Program (No. 201210488002) and Open Foundation of Hubei Province Key Laboratory of Coal Conversion and New Carbon Materials (No. WKDM201106) are gratefully acknowledged. Notes

The authors declare no competing financial interest.

■

REFERENCES

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Figure 9. Molar Gibbs energy of solution at 333 K as a function of the solubility: ▼, acetone−water; ▲, N,N-dimethylformamide−water; ●, isopropyl alcohol−water; ■, ethanol−water.

binary mixed solvents as a function of temperature. The experimental solubilities and correlation equations in this work can be used as essential data and models in the industrial manufacture process of L-valine. 3.3. Prediction of Dissolution Enthalpy, Entropy, and the Molar Gibbs Energy. The thermodynamic functions of ΔsolHo, ΔsolSo and ΔsolGo at 313.15 K were calculated and listed in Table 9. The dissolving process of L-valine in each binary solution is endothermic because all values of ΔsolHo and ΔsolGo in Table 9 are positive. A good linear correlation between the molar Gibbs energy of L-valine at 313.15 K in the binary 2739



Article

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Measurement and Correlation of Solubility of l-Valine in Water +

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