Solubility of L-tartaric Acid in Ethanol, Propanol,Isopropanol, n-Butanol, Acetone and Acetonitrile

Wenge Yang • Kai Wang • Yonghong Hu • Fei Shen • Jing Feng

Received: 9 January 2012 / Accepted: 8 April 2012 / Published online: 8 March 2013� Springer Science+Business Media New York 2013

Abstract The solubility of L-tartaric acid was measured in ethanol, propanol, isopropa-

nol, n-butanol, acetone and acetonitrile in the temperature range 281.15 and 324.25 K

under atmospheric pressure by a gravimetric method. The solubility of L-tartaric acid in

those selected solvents increases with increasing temperature. The apparent molar

enthalpies of solution of L-tartaric acid in the selected solvents were estimated from the

solubility data. The solubility results were correlated with the van’t Hoff equation, the

modified Apelblat equation, and the kh equation. Agreement with the experimental data

was very good in all cases. The experimental results could be useful for optimizing the

purification process of L-tartaric acid in industry.

Keywords L-tartaric acid � Solubility � Van’t Hoff equation � Apelblat equation � khequation

1 Introduction

Because of the effect of two chiral carbon atoms in its molecular structure, tartaric acid has

three different optical isomers, namely D-, L- and DL-tartaric acid. L-tartaric acid is a natural

organic acid occurring widely in fruits, especially in grapes and berries [1]. It was initially

derived from the byproduct of wine making by Scheele in 1769 [2]. The largest use of

L-tartaric acid is as food additive in soft drinks, wine, candy, bread and some colloidal

sweetmeats [3, 4], because it is considered natural and safe to the body [5]. In addition,

L-tartaric acid has been used as a chemical resolving agent to resolve DL-amino-butanol,

which is an intermediate for an anti-tubercular drugs [6]. It is also used in electroplating

W. Yang � K. Wang � Y. Hu (&)College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology,No. 200, North Zhongshan Road, Nanjing 210009, Chinae-mail: yonghonghu11@126.com

Y. Hu � F. Shen � J. FengJiangsu Engineering Technology Research Center of Polypeptide Pharmaceutical,Nanjing 210038, China

123

J Solution Chem (2013) 42:485–493DOI 10.1007/s10953-013-9960-6

[7], dyeing [8] and chemical analysis [9]. In industrial manufacturing, natural products are

still the main source of L-tartaric acid, while only DL-tartaric acid can be produced by

chemical synthesis. In recent years, biosynthetic pathways of tartaric acid have been

attracting more and more attention for producing L- or D-tartaric acid of high purity and

safety, which are the requirements in food and drug quality and management [10].

This work is part of a research project on the production of L-tartaric acid by micro-

organism fermentation. L-tartaric acid is crystallized from aqueous solution in the purifi-

cation step by our group and separated from soluble impurities (mainly the inorganic salts)

that come from the fermentation broth. The finished product is obtained after drying. It

should be noted that the product from aqueous cyrstallization needs longer drying times

than product containing only organic solvent. In order to save time and energy, an alternate

solvent system is required. This work is aimed at determining the solubility of L-tartaric

acid in different organic solvents and to test the capability of the selected solubility

correlation models (the van’t Hoff equation, the modified Apelblat equation and the khequation) to correlate the experimental data. Through the results, we may select an organic

solvent to replace water as the crystallization solvent for L-tartaric acid.

In this work, the solubility data of L-tartaric acid in pure ethanol, propanol, isopropanol,

n-butanol, acetone and acetonitrile were measured in the temperature range 281.15 and 324.25 K

under atmospheric pressure by the gravimetric analysis method. The experimental data were

correlated using the van’t Hoff equation and, the modified Apelblat equation, and the kh equation.

2 Experimental

2.1 Materials and Apparatus

L-tartaric acid (Fig. 1; C4H4O6; CAS RN: 87-69-4; molecular mass 150.09 g�mol-1) with

mass fraction purity [99.5 % was purchased from Sinopharm Chemical Regent Co., Ltd.

The melting point was determined by a melting point apparatus (model: HCRD-2C) that

was supplied by Chengdu Huacheng Instruments Co., Ltd. All the organic solvents (HPLC

grade) used for the experiments were supplied by Shanghai Shenbo Chemical Co., Ltd. and

used without further purification. More details about the purities of solvents along

with their CAS registry numbers are listed in Table 1. A smart thermostatic bath (model:

DC-2006) was provided by Ningbo Scientz Biotechnology Co., Ltd. with an uncertainty of

±0.1 K. The analytical balance (model: BSA224S) was provided by Sartorius Scientific

Instruments (Beijing) Co., Ltd. with an uncertainty of ±0.0001 g.

2.2 Methods

In the experiments, the gravimetric method was used to study the solubility of L-tartaric

acid in different organic solvents. The method for solubility measurement is similar to that

Fig. 1 Chemical structureof L-tartaric acid

486 J Solution Chem (2013) 42:485–493

123

described in the literature [11, 12]. The temperature was controlled and calibrated using the

smart thermostatic bath. A Sartorius balance was used for weighing the solute and solution.

An 8 mL of organic solvent and excess L-tartaric acid were placed into a 10 mL glass

test tube with stopper, and stirred continuously using a magnetic stirrer at the required

temperatures in the thermostatic bath. A time period of 24 h was used to ensure that solid–

liquid equilibrium was established in the test tube. At least 6 h was allowed after turning

off the stirring to settle the solution. A 1 mL volume of clear saturated upper solution was

taken from the test tube and quickly transferred into a 5 mL beaker and covered to prevent

the loss of solvent, and the total weight was measured immediately. Before measuring the

weight of the beaker plus residue containing no solvent, it was kept in a dryer oven at

308 K for 7 days. Each experiment was repeated three times to obtain mean value of the

solubility. The saturated mole fraction solubility of L-tartaric acid (x1) in each solvent can

be calculated from the following equation:

x1 ¼m1=M1

m1=M1 þ m2=M2

ð1Þ

where m1 and m2 represent the mass of the solute and the solvent, and M1 and M2 are the

molecular weight of the solute and the solvent, respectively. The estimated uncertainty of

the experimental solubility values is about 2.0 %. The uncertainty in the solubility values is

the result of uncertainties in the temperature measurements, weighing procedure, insta-

bilities of the water bath, and excess addition of L-tartaric acid.

2.3 Test of the Apparatus

To prove the reliability of the measurements, the solubility of NaCl in water was also

measured and compared with the values reported in the literature [13, 14]. The experi-

mental data agreed with the reported values with a mean relative deviation of 0.32 %. The

measured values are listed in Table 2.

3 Results and Discussion

The measured mole fraction solubility of L-tartaric acid in pure ethanol, propanol, iso-

propanol, n-butanol, acetone and acetonitrile at the temperature range from 281.15 and

324.25 K are presented in Table 3. The relationship between temperature and mole frac-

tion solubility in each different solvens were described by the van’t Hoff equation, the

modified Apelblat equation and the kh model.

The temperature dependence of the solubility of L-tartaric acid in the selected solvents

can be correlated by the following van’t Hoff equation:

lnðx1Þ ¼ Aþ B=ðT=KÞ ð2Þ

Table 1 Mass fraction percentpurities of solvents along withtheir CAS registry numbers

Solvent Mass % CASNo.

Solvent Mass % CASNo.

Acetone C99.5 67-64-1 Ethanol C99.7 64-17-5

Acetonitrile C99.9 75-05-8 n-Butanol C99.0 71-36-3

Propanol C99.5 67-56-1 Isopropanol C99.7 67-63-0

J Solution Chem (2013) 42:485–493 487

123

where x1 is the mole fraction solubility of L-tartaric acid, T is the corresponding temper-

ature in K, and A and B are parameters of this equation. The parameters A and B are listed

in Table 4.

The modified Apelblat equation, which was previously used by Apelblat [15–17], is:

ln x1ð Þ ¼ Aþ B

T=Kþ C lnðT=KÞ ð3Þ

where x1 is the mole fraction solubility of L-tartaric acid, T is the experimental temperature

in Kelvin, and A, B and C are regression parameters and are listed in Table 5. The

constants A and B represent the variation in the solution activity coefficient and provide an

indication of the effect of non-ideal solution behavior on the solute solubility, while the

constant C reflects the temperature influence on the enthalpy of fusion [18].

The kh model, which is semi-empirical, can be written as follows [19, 20]:

ln 1þ kð1� x1Þx1

� �¼ kh

1

T=K� 1

Tm=K

� �ð4Þ

where x1 is the mole fraction solubility of L-tartaric acid, T and Tm are the experimental

temperature and normal melting temperature of L-tartaric acid in K, respectively. k and

h are model parameters which are presented in Table 6.

The root-mean-square deviations (RMSDs), together with the relative average deviation

(RAD) for the van’t Hoff equation, the modified Apelblat equation, and the kh model are

also listed in Tables 4, 5 and 6, respectively. The RMSD is defined as:

RMSD ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiPNi¼1

ðxc1ðiÞ � xe

1ðiÞÞ2

N

vuuutð5Þ

where N is the number of experimental points obtained in each set (which is equal to the

number of temperatures used), xc1 denotes the calculated solubility values, and xe

1 denotes

the experimental solubility values.

The relative deviations (RD) between the experimental and the calculated values are

also presented in Table 3. The RD can be obtained according to:

RD ¼ xe1 � xc

1

xe1

ð6Þ

The relative average deviations (RAD) are calculated by:

RAD ¼ 1

N

XN

i¼1

xe1ðiÞ � xc

1ðiÞxe

1ðiÞ

���������� ð7Þ

Table 2 Mole fraction solubility of NaCl in water

NaCl

T/K 293.15 303.15 313.15 323.15

x 0.0999 ± 0.0002 0.1004 ± 0.0005 0.1013 ± 0.0003 0.1022 ± 0.0001

x (lit.) 0.0996 0.1001 0.1009 0.1019

102 RD 0.30 0.30 0.39 0.29

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Table 3 Mole fraction solubility (x1) of L-tartaric acid in different organic solvents in the temperature range(281.15–324.25) K

T/K 102 x1 102 RD T/K 102 x1 102 RD

Ethanol

281.15 3.2078 ± 0.0013 0.20 305.15 8.4289 ± 0.0008 1.28

285.15 3.8139 ± 0.0007 –0.95 309.15 9.6094 ± 0.0011 0.06

289.15 4.5882 ± 0.0002 1.35 313.15 10.9337 ± 0.0007 –1.04

293.15 5.3068 ± 0.0004 0.12 316.85 12.6180 ± 0.0009 0.62

297.15 6.1382 ± 0.0012 –0.73 320.25 14.0629 ± 0.0008 0.05

301.15 7.1224 ± 0.0008 –0.88 324.25 16.0173 ± 0.0003 –0.09

Propanol

281.15 2.0969 ± 0.0014 –0.88 305.15 4.6520 ± 0.0005 –1.67

285.15 2.4243 ± 0.0006 –0.61 309.15 5.3228 ± 0.0008 –0.51

289.15 2.8542 ± 0.0006 1.80 313.15 5.9869 ± 0.0004 –0.81

293.15 3.2024 ± 0.0008 –0.23 316.85 6.8426 ± 0.0006 1.64

297.15 3.6600 ± 0.0002 –0.11 320.25 7.4146 ± 0.0006 –0.14

301.15 4.2353 ± 0.0005 1.56 324.25 8.2936 ± 0.0007 –0.26

Isopropanol

281.15 2.2398 ± 0.0008 –1.56 305.15 4.5681 ± 0.0012 0.56

285.15 2.5507 ± 0.0017 –0.45 309.15 5.0361 ± 0.0014 –0.72

289.15 2.9256 ± 0.0007 1.52 313.15 5.6496 ± 0.0001 –0.13

293.15 3.2169 ± 0.0004 –0.57 316.85 6.1953 ± 0.0005 –0.89

297.15 3.6460 ± 0.0014 0.50 320.25 6.8650 ± 0.0010 0.30

301.15 4.0959 ± 0.0011 0.82 324.25 7.6271 ± 0.0003 0.26

n-Butanol

281.15 1.7715 ± 0.0009 –0.27 305.15 3.4659 ± 0.0014 0.15

285.15 2.0019 ± 0.0015 0.13 309.15 3.8594 ± 0.0004 0.71

289.15 2.2736 ± 0.0013 1.32 313.15 4.2289 ± 0.0012 0.10

293.15 2.5121 ± 0.0004 0.06 316.85 4.6394 ± 0.0011 0.04

297.15 2.7693 ± 0.0003 –1.16 320.25 5.0153 ± 0.0009 –0.02

301.15 3.0895 ± 0.0007 –0.91 324.25 5.5174 ± 0.00013 –0.11

Acetone

81.15 1.4370 ± 0.0007 –0.92 305.15 2.3908 ± 0.0007 0.28

285.15 1.5736 ± 0.0013 –0.53 309.15 2.5635 ± 0.0001 –0.50

289.15 1.7422 ± 0.0006 1.13 313.15 2.7635 ± 0.0005 –0.61

293.15 1.9024 ± 0.0016 1.56 316.85 2.9669 ± 0.0021 –0.44

297.15 2.0071 ± 0.0002 –1.27 320.25 3.2162 ± 0.0007 1.34

301.15 2.2087 ± 0.0008 0.26 324.25 3.3970 ± 0.0004 –0.44

Acetonitrile

281.15 0.0762 ± 0.0014 –3.00 305.15 0.2214 ± 0.0015 0.39

285.15 0.0929 ± 0.0005 –1.06 309.15 0.2584 ± 0.0003 –0.46

289.15 0.1118 ± 0.0002 –0.15 313.15 0.3030 ± 0.0017 –0.57

293.15 0.1339 ± 0.0009 0.53 316.85 0.3504 ± 0.0008 –0.65

297.15 0.1610 ± 0.0005 1.83 320.25 0.4030 ± 0.0012 0.09

301.15 0.1890 ± 0.0005 1.08 324.25 0.4710 ± 0.0007 0.30

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As can be seen from the small RMSDs in Tables 3, 4, 5, and 6, the calculated solu-

bilities of L-tartaric acid in the six pure organic solvents show good agreement with the

experimental solubilities. Taking the solubility data in ethanol, propanol, isopropanol,

n-butanol, acetone and acetonitrile fitted by the modified Apelblat equation as an illus-

tration, the relative average deviations are 0.61, 0.85, 0.69, 0.41, 0.77 and 0.84 %,

respectively; the absolute values of relative deviations among all of the values do not

exceed 3.00 %, which indicates that the modified Apelblat equation is suitable for corre-

lating the solubility data of L-tartaric acid in the selected pure solvents. The same con-

clusion can be drawn after analyzing the solubility data that were fitted by the van’t Hoff

equation and the kh model. However, the modified Apelblat equation is more accurate than

the van’t Hoff equation and the kh equation for the systems. These results suggest that the

experimental data and the correlation equations used in this work are important for the

purification process of L-tartaric acid.

The xe/T-curves of L-tartaric acid in all of the selected pure solvents are presented in

Fig. 2. It can clearly be seen from the figures that the solubility of L-tartaric acid in each of

the selected solvents is a function of temperature and increases with increasing tempera-

ture, but the increment of solubility with temperature is different in each of the different

pure solvents. It can be observed from Fig. 2 that all of the solubilities follow the order:

ethanol [propanol &isopropanol [n-butanol [acetone [acetonitrile. This result shows

Table 4 Parameters of the van’tHoff equation for L-tartaric acidin the different organic solvents

Solvent A B 104 RMSD 102 RAD

Ethanol 8.61 -3386.47 6.06 0.64

Propanol 6.47 -2905.53 5.06 0.79

Isopropanol 5.41 -2591.76 4.51 0.83

n-Butanol 4.51 -2403.20 1.82 0.46

Acetone 2.23 -1820.62 2.16 0.68

Acetonitrile 6.50 -3847.56 0.23 0.92

Table 5 Parameters of themodified Apelblat equationfor L-tartaric acid in the differentorganic solvents

Solvent A B C 104 RMSD 102 RAD

Ethanol 2.26 -3096.50 0.94 5.92 0.61

Propanol -7.86 -2252.36 2.13 4.99 0.85

Isopropanol -56.24 212.56 9.17 3.04 0.69

n-Butanol -8.22 -1824.49 1.89 1.73 0.41

Acetone -22.58 -695.91 3.70 2.03 0.77

Acetonitrile -61.50 -736.67 10.10 0.16 0.84

Table 6 Parameters of the khequation for L-tartaric acid in thedifferent organic solvents

Solvent k h 104 RMSD 102 RAD

Ethanol 3.71 978.77 8.48 1.03

Propanol 0.92 3160.03 5.04 0.80

Isopropanol 0.58 4351.41 3.89 0.68

n-Butanol 0.32 7047.36 1.88 0.52

acetone 0.08 17564.86 2.15 0.87

Acetonitrile 0.10 36563.63 0.20 0.71

490 J Solution Chem (2013) 42:485–493

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that the polarity of the solvents is not the only factor that determines the solubility of

L-tartaric acid in the solvents, as the polarity of the selected solvents has the following

order: acetonitrile[ethanol[acetone[isopropanol &propanol[n-butanol. Figure 1 gives

the chemical structure of L-tartaric acid, which shows that it contains four hydroxyls. The

structural similarity between L-tartaric acid and alcohols due to the hydroxyl group sig-

nificantly enhances the solubility. Furthermore, the solubility decreases as the number of

carbons in the n-alcohols increases, which indicates a decreasing solubility with decreasing

solvent polarity.

From the solubility data of L-tartaric acid, we find that ethanol has the potential of being

a good solvent for the crystallization process because L-tartaric acid has low solubility at

low temperatures and high solubility at high temperatures in ethanol. Compared with

water, ethanol possesses the merits of safety, recovery, and is more easily removed.

The temperature dependence of solubility is related to the molar enthalpy of solution

[21]:

olnx1

oð1=TÞ

� �1þ ð olnc

olnx1

ÞT� �

¼ �DsolHm

Rð8Þ

Since the value of the activity coefficient (c) is unknown, this term is neglected and only

the apparent or van’t Hoff molar enthalpy of solution (Dappsol Hm) is accessible [21, 22]:

olnx1

oð1=TÞ

� ¼ �Dapp

sol Hm

Rð9Þ

This equation can also be written as [23]:

olnx1

oT

� ¼ Dapp

sol Hm

RT2ð10Þ

where x1 is the mole fraction solubility, R denotes the universal gas constant

(8.314 J�mol�1�K�1) and T is the corresponding absolute temperature.

Fig. 2 Mole fraction solubility (x1) of L-tartaric acid versus the temperature (T) in selected pure solvents:times ethanol, circle propanol, open triangle isopropanol, filled triangle n-butanol, square acetone, asteriskacetonitrile. Solid lines calculated from Eq. 2

J Solution Chem (2013) 42:485–493 491

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The van’t Hoff molar enthalpy of solution differs from the calorimetric enthalpy of

solution and can be obtained from the slope of the solubility curve in a so-called van’t Hoff

plot, where lnx1 is plotted versus 1/T. The linear lnðxÞ versus T�1-curves of L-tartaric acid in

the selected organic solvents are shown in Fig. 3. From the data, values of Dappsol Hm were

calculated for L-tartaric acid in ethanol, propanol, isopropanol, n-butanol, acetone and ace-

tonitrile and are 28.15, 24.09, 21.30, 19.91, 15.07, 31.69 kJ�mol-1, respectively. A high van’t

Hoff molar enthalpy of solution indicates a strong temperature dependence of solubility [21].

4 Conclusions

Solubility data were measured for L-tartaric acid in a total of six pure organic solvents in

the temperature range 281.15 to 324.25 K. We can draw the following conclusions: (1) the

solubility of L-tartaric acid in the selected solvents increases with increasing temperature,

but the solubility increments with temperature vary for different solvents; (2) the solubility

data can be successfully correlated using the van’t Hoff equation, the modified Apelblat

and the kh equations; (3) the experimental solubility values and the parameters can be used

for optimizing the purification process of L-tartaric acid in industry.

Acknowledgments This research work was financially supported by the Natural Science Foundation ofChina (NSFC) (No. 31171644). This research work was also supported by Specialized Research Fund for theDoctoral Program of Higher Education (20113221110005). We thank the editors and the anonymousreviewers.

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