Solubility, Density, and Metastable Zone Width of Pyridoxine

Article pubs.acs.org/jced

Solubility, Density, and Metastable Zone Width of Pyridoxine Hydrochloride in Water and Ethanol Solvent Mixtures Kun Zhou,*,†,‡ Yueyong Yan,† Lianying An,†,‡ Dongni Xiang,† and Hongbin Wang† †

College of Materials and Chemistry & Chemical Engineering, and ‡Mineral Resources Chemistry Key Laboratory of Sichuan Higher Education Institutions, Chengdu University of Technology, Chengdu 610059, China ABSTRACT: The solubility of pyridoxine hydrochloride in water and ethanol solvent mixtures was measured using a laser monitoring observation technique at the temperature range from (278.15 to 323.15) K. The mole fraction of ethanol in the solvent mixtures (x3) ranges from 0.0 to 0.6012. For the seven group data studied, the experimental solubility data were well-correlated with the results calculated by means of a semiempirical equation. Densities of pyridoxine hydrochloride in solvent mixtures were investigated at temperatures from (293.15 to 323.15) K. The effects of ethanol mole fraction, cooling rate, and saturation temperature on the metastable zone width (MZW) were also studied. The results show that the MZW of pyridoxine hydrochloride becomes narrower by increasing the saturation temperature, increasing ethanol mole fraction, and reducing the cooling rate. For the density and the MZW, all results were correlated by empirical equations.

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INTRODUCTION Pyridoxine hydrochloride with the chemical name 5-hydroxyl-6methyl-3,4-pyridine dimethanol hydrochloride, also known as vitamin B6 is a colorless or white crystal, and is widely used in over-the-counter preparations as well as for medical therapy. The vitamins of the B group are water-soluble compounds and contain the pyridine ring in their molecules.1 Pyridoxine hydrochloride was the first of the B6 group of vitamins to be isolated and it is essential in living organisms for its participation in more than 100 enzymatic reactions, including the transfer of amino groups, water or acids in metabolism of proteins, the metabolism of amino acids and the maintenance of body cells. In industrial manufacturing, pyridoxine hydrochloride is crystallized from pure water in the purification step, and the final crystal is granular. However, it is well recognized that the particle size plays a significant role in the dissolution rate in solvents, especially for drugs. The reduction of particle size to micro- and nanometer range has improved the solubility of drugs in the production practice. The application of binary solvent mixtures is a very prevalent and highly powerful technique of transforming (decreasing or increasing) the solubility of a solute. The solubility of solutes can be greatly changed by using binary solvent mixtures. Under some circumstances, the solubility even can be altered by several orders of magnitude in solvent mixtures,2,3 whereas, only solubility in some pure solvents for example acetone, methanol, chloroform, dichloromethane, and ethanol was reported in much of the literature.4 To design an optimized crystallization process and crystallizer, the solubility, density, and metastable zone width (MZW) values of pyridoxine hydrochloride in solvent mixtures are needed. Unfortunately, the thermody© 2015 American Chemical Society

namic data of pyridoxine hydrochloride in solvent mixtures have never been reported. In this work, the solubility of pyridoxine hydrochloride in binary water and ethanol solvent mixtures was measured at the temperature range of (278.15 to 323.15) K, while the density and MZW data were measured in the temperature range from (293.15 to 323.15) K under atmospheric pressure. And the concentration of pyridoxine hydrochloride was determined by ultraviolet−visible spectroscopy (UV−vis).5

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EXPERIMENTAL SECTION Materials. A white powered crystal of pyridoxine hydrochloride (C8H11NO3·HCl, molecular mass 205.64, Figure 1) purchased from Guangzhou Shu-nuo Chemical Engineering Co., Ltd., China, was used to measure the thermodynamic data. It was prepared by recrystallization from pure water three times in the laboratory. And it was washed with chloroform, dried in a vacuum drying oven at 333.15 K for 24 h, and stored in

Figure 1. Chemical structure of pyridoxine hydrochloride. Received: July 6, 2015 Accepted: November 5, 2015 Published: November 13, 2015 307

DOI: 10.1021/acs.jced.5b00552 J. Chem. Eng. Data 2016, 61, 307−312

Journal of Chemical & Engineering Data

Article

Table 1. Detailed Information of Materials Used in the Study chemical name pyridoxine hydrochloride ethanol a

source

initial mass fraction purity

purification method

final mass fraction purity

analysis method

≥ 0.980

recrystallization

≥ 0.990

HPLCa

≥ 0.995

none

Guangzhou Shu-nuo Chemical Engineering Co., Ltd., China Chengdu Ke-long Chemical Reagent Co., Ltd., China

GCb

b

High-performance liquid chromatography. Gas−liquid chromatography.

chloride is 325 nm. Using the standard solution in the appropriate concentration range, the working curve is prepared for the concentration estimation of pyridoxine hydrochloride Measurement of Density. The density of pyridoxine hydrochloride in water + ethanol was determined using a U type vibrating-tube digital densimeter (Density/Specific Gravity Meter DA 505, KEM Co, Ltd., Japan). Before experiment, the digital densimeter was calibrated with deionized and doubledistilled water at the experimental temperature. The saturation solution was maintained in a thermostat bath for 2 h. At the test temperature, the solution density can be read directly from densimeter after the sample is pumped into the densimeter through the sucker. The standard uncertainty in the cell temperature was 0.01 K. The standard uncertainty in density measurements is 3 kg/m3. Measurement of Metastable Zone Width (MZW). MZW data of pyridoxine hydrochloride in water and ethanol solvent mixtures were measured by the laser method at the temperatures range of (293.15 to 323.15) K. The main factors affecting the MZW are the cooling rate, the saturation temperature, the stirring rate, the presence of impurities, and the addition rate of antisolvent.8 First, the saturation solution preparation method is the same as measurement of solubility and density. Then, a certain volume of sample was added into jacketed crystallizer, and in order to eliminate microcrystals, the mixture was heated for 10 min at 3 °C higher than saturation temperature before cooling. Finally, under a constant stirring rate, the sample was cooled at five cooling rates of (5, 10, 15, 20, and 25) K·h−1. When the crystals appeared, the intensity of laser beam penetrating the crystallizer significantly reduced. The saturation temperature and nucleation temperature were denoted as To and Tnuc, respectively. The MZW (ΔTmax) can be calculated by eq 3.9

desiccators. The mass fraction of pyridoxine hydrochloride, measured by HPLC, is greater than 99.0 %. Ethanol was analytical grade reagents purchased from Chengdu Ke-long Chemical Reagent Company. Its mass fraction was better than 99.5 %. The water used in the experiment was distilled by an ultrapure water unit in the laboratory. More detailed information on the chemicals used in the study is shown in Table 1. Measurement of Solubility. The measurement apparatus of the solubility is similar to that described in the literature.6 A 150 mL jacketed vessel was used to determine the solubility. The temperature fluctuation was controlled within ± 0.05 K through a thermostat bath (type 501, China). A mercury-inglass thermometer (standard uncertainty of 0.05 K) was used for the measurement of the temperature in the vessel. The mixtures of pyridoxine hydrochloride and solvent in the vessel were stirred with a magnetic stirrer. To prevent the evaporation of the solvent, a condenser vessel was introduced. The concentration of pyridoxine hydrochloride was determined by UV−vis analysis. The masses of the samples and solvents were determined using an analytical balance (Sartorius CP124S, Germany) with the standard uncertainty of 0.1 mg. In this study, the solubility determination of pyridoxine hydrochloride is conducted by adding excessive amounts of pyridoxine hydrochloride to the solution that is stirred and kept at a settled temperature. At the outset, predetermined amounts of mixed solvent (water + ethanol) were loaded into a jacketed vessel, and after that, masses of pyridoxine hydrochloride were transferred into the solvent. According to the concentration of solute determined at different dissolution times, the solution attained equilibrium when the concentration did not change any more. Then the magnetic stirrer was turned off. After the solution settle for 2 h, the upper portion of the solution was taken, filtered, and diluted into a 50 mL volumetric flask. To prepare the solutions for UV−vis analysis, they were diluted to 50 mL with the same system.7 To reduce the error of experiment, the results were taken from an average of three measurements for each temperature. The standard uncertainty in the mole fraction solubility values was estimated to 0.05. The mole fraction solubility x1 and the composition of ethanol in solvent mixtures x3 were calculated by eq 1 and eq 2: x1 =

m1/M1 m1/M1 + m2 /M 2 + m3 /M3

x3 =

m3 /M3 m2 /M 2 + m3 /M3

ΔTmax = To − Tnuc

■

(3)

RESULTS AND DISCUSSION

Solubility. The solubilities of pyridoxine hydrochloride in water and ethanol solvent mixtures under different temperatures are presented in Table 2 and plotted in Figure 2. The temperature dependence of pyridoxine hydrochloride solubility in solvents mixtures can be expressed by the following modified empirical equation.10,11

(1)

ln(x1) = A +

(2)

where m1, m2 and m3 are the mass of the solute, water and ethanol, respectively, and M1, M2 and M3 represent the molecular weight of the solute, water and ethanol, respectively. To determine the concentration of pyridoxine hydrochloride in the solution, the absorbance of experimental sample and the standard solution was measured at 325 nm, because the maximum absorption wavelength (λmax) of pyridoxine hydro-

B + C ln(T /K) T /K

(4)

where x1 is the mole fraction solubility of pyridoxine hydrochloride, T is the absolute temperature, and A, B, and C are the parameters. The calculated solubility values of pyridoxine hydrochloride (xcalcd) are also listed in Table 2. The values of parameters A, B, and C and the root-mean-square deviations (rmsd) are given in Table 3. The rmsd values shown in Table 3 and Table 5 are defined as 308



Article

Table 2. Experimental Mole Fraction Solubilities x1 of Pyridoxine Hydrochloride in Binary System of Water (2) + Ethanol (3) at Experimental Pressure P = 0.1 MPa and Different Saturation Temperaturesa,b T/K

102x1

278.15 283.15 288.15 293.15 298.15

1.066 1.282 1.48 1.626 1.886

278.15 283.15 288.15 293.15 298.15

0.817 0.9196 1.0545 1.2141 1.425

278.15 283.15 288.15 293.15 298.15

0.5512 0.6435 0.7618 0.8788 1.0114

278.15 283.15 288.15 293.15 298.15

0.376 0.44 0.528 0.614 0.778

278.15 283.15 288.15 293.15 298.15

0.363 0.434 0.498 0.576 0.666

278.15 283.15 288.15 293.15 298.15

0.299 0.323 0.364 0.425 0.484

278.15 283.15 288.15 293.15 298.15

0.179 0.197 0.225 0.246 0.268

102(x1 − x1calc)

T/K

x3 = 0.0000 −0.006 303.15 0.021 308.15 0.014 313.15 −0.061 318.15 −0.035 323.15 x3 = 0.1002 0.031 303.15 −0.014 308.15 −0.037 313.15 −0.043 318.15 −0.002 323.15 x3 = 0.2005 0.005 303.15 −0.006 308.15 −0.001 313.15 −0.005 318.15 0.000 323.15 x3= 0.2998 0.006 303.15 −0.007 308.15 −0.006 313.15 −0.015 318.15 0.045 323.15 x3 = 0.4005 −0.003 303.15 0.005 308.15 −0.001 313.15 0.001 318.15 0.007 323.15 x3 = 0.5011 0.006 303.15 −0.009 308.15 −0.010 313.15 0.004 318.15 0.012 323.15 x3 = 0.6012 0.000 303.15 −0.002 308.15 0.004 313.15 0.001 318.15 −0.002 323.15

102x1

102(x1 − x1calc)

2.222 2.522 2.666 2.818 3.29

0.055 0.100 −0.018 −0.133 0.070

1.6359 1.8145 1.9988 2.0824 2.1736

0.038 0.046 0.065 −0.010 −0.066

1.1505 1.287 1.4144 1.5678 1.6783

0.006 0.007 −0.004 0.012 −0.013

0.834 0.95 1.083 1.219 1.344

−0.010 −0.012 −0.003 0.005 −0.002

0.745 0.847 0.931 1.089 1.182

−0.005 −0.001 −0.022 0.023 −0.003

0.549 0.595 0.605 0.724 0.818

0.021 0.007 −0.048 0.001 0.019

0.297 0.325 0.354 0.384 0.424

0.000 0.000 −0.001 −0.003 0.003

Figure 2. Solubility of pyridoxine hydrochloride in binary system of water + ethanol mixture along temperature: ●, x3 = 0.0000; ○, x3 = 0.1002; △, x3 = 0.2005; ×, x3= 0.2998; ▼, x3 = 0.4005; □, x3 = 0.5011; +, x3 = 0.6012.

Table 3. Parameters of eq 3 for Pyridoxine Hydrochloride in Binary System of Water (2) + Ethanol (3) Mixture A

B

C

104 rmsd

0 0.1002 0.2005 0.2998 0.4005 0.5011 0.6012

131.89 221.76 175.22 150.19 55.34 −11.14 −1.80

−7938.71 −11878.23 −9955.78 −9123.89 −4690.41 −1446.17 −1634.23

−19.17 −32.68 −25.70 −21.85 −7.83 1.87 0.24

6.45 4.06 0.71 1.64 1.08 1.88 0.22

increasing temperature; the solubility decreases with increasing mole fraction of ethanol in the solvent mixtures. In the process of industrial crystallization, the initial temperature of crystallization can be appropriately increased to improve the production capacity of unit volume. According to Figure 2, it is obvious to find that the solubility of pyridoxine hydrochloride in solvent mixtures is less than the solubility in pure water; when the concentration of ethanol in the solution is relatively small, the effect of temperature on the solubility is obvious; and the higher is the concentration of ethanol, the smaller is the effect of temperature. From Table 1, the calculated solubility of pyridoxine hydrochloride shows good agreement with the experimental values; and the value of rmsd in Table 3 is less than 7·10−4, which can be used as the basic data to guide industrial production. Density of Pyridoxine Hydrochloride in Water + Ethanol Mixtures. The density of pyridoxine hydrochloride in water + ethanol mixtures was measured within a temperature range of (293.15 to 323.15) K and in mole fraction (x3) range from 0 to 0.6. An average value taken from three measurements was considered as the final result for each temperature. All experimental densities are listed in Table 4. With the increase of saturation temperatures, there is a certain increase in density when the mole fraction x3 is 0 or 0.2, while the density of pyridoxine hydrochloride in solvent mixtures decrease slightly when a significant increase in the mole fraction of antisolvent ethanol. The experimental data of density were fitted to eq 6 below as a function of absolute temperature (T) and mole fraction of pyridoxine hydrochloride (x1)13

a

x1, x1calc, and x3 represent the experimental solubility data, the calculated solubility data by eq 4 with parameters correlated from the experimental solubility data, and the mole fraction of ethanol in solvent mixtures, respectively. bThe standard uncertainty of T is u(T) = 0.05 K, and the standard uncertainty of P is u(P) = 0.005 MPa; the standard uncertainty of x3 is u(x3) = 0.05; the relative standard uncertainty u is ur(x1) = 0.05.

⎡ ∑N (x − x calc)2 ⎤1/2 1, i 1, i ⎥ rmsd = ⎢ i = 1 ⎢⎣ ⎥⎦ N

x3

(5)

where N is the number of experimental trials.12 As it can be seen from Figure 2, and Table 3, the solubility of pyridoxine hydrochloride in binary water + ethanol solvent mixtures is a function of temperature, and the solubility increases with 309



Article

Table 4. Experimental Density ρ of Pyridoxine Hydrochloride in the Binary System of Water (2) + Ethanol (3) at Experimental Pressure P = 0.1 MPa and Different Saturation Temperaturesa,b T0/K

ρ/(kg·m−3)

102(ρ − ρcalc)

293.15 298.15 303.15 308.15

1093.5 1104.7 1111.0 1120.8

−0.087 0.179 −0.080 −0.077

293.15 298.15 303.15 308.15

845.7 848.6 852.2 862.2

0.105 −0.037 −0.257 0.031

293.15 298.15 303.15 308.15

782.1 774.5 774.4 767.0

0.035 −0.150 0.224 −0.126

293.15 298.15 303.15 308.15

741.7 737.5 736.2 732.6

0.057 −0.114 0.076 −0.023

T0/K

ρ/(kg·m−3)

102(ρ − ρcalc)

313.15 318.15 323.15

1133.3 1141.5 1154.6

0.141 −0.108 0.032

313.15 318.15 323.15

872.5 881.0 890.0

0.235 0.019 −0.097

313.15 318.15 323.15

766.3 764.1 764.0

−0.023 0.069 −0.029

313.15 318.15 323.15

729.9 729.2 724.8

−0.052 0.099 −0.043

x3 = 0.0000

x3 = 0.2005

x3 = 0.4005

x3 = 0.6012

a

x3 represents the mole fraction of ethanol in solvent mixtures. bThe standard uncertainty of T is u(T) = 0.05 K, and the standard uncertainty of P is u(P) = 0.005 MPa; the standard uncertainty of x3 is u(x3) = 0.05; the relative standard uncertainty u is u(ρ) = 3 kg/m3.

Table 5. Parameters, k1, k2, k3, and k4 of eq 6 x3

k1

k2

k3

k4

104 rmsd

0 0.2005 0.4005 0.6012

655.0 1005.6 1059.9 818.1

−13573.0 −37092.2 −47985.3 −56964.6

1.5 −0.6 −0.8 −0.1

43.3 133.5 139.7 137.5

10.98 14.36 11.72 7.27

−3

ρ /(g·cm ) = k1 + k 2x1 + k 3(T /K) + k4x1(T /K)

Table 6. MZW Data for Pyridoxine Hydrochloride in Water + Ethanol Solvents with the Temperature Range from (293.15 to 323.15) K and Pressure P = 0.1 MPaa ΔTmax/K

(6)

where ρ is the density and T is temperature. And the values of coefficients k1, k2, k3, and k4 of eq 6 are listed in Table 5. The deviation between the experimental and calculated values is less than 0.003 g/cm3. Metastale Zone Width. According to Nývlt’s studies,14−16 the relationship between the supersaturation ΔCmax and the supercooling ΔTmax can be expressed by ΔCmax =

⎛ dC ⎞ ⎜ ⎟ΔT ⎝ dT ⎠ max

(7)

where dC/dT is the slope of the solubility of pyridoxine hydrochloride dependence on the temperature change. In industrial crystallization, the primary nucleation rate B0 is generally expressed by empirical formula:17 m B0 = k 0ΔCmax

(8)

where k0 denotes the nucleation rate constant, and m is the nucleation order. When the supersaturation is produced by cooling, the nucleation rate can be expressed by the production rate of supersaturation.

⎛ dC ⎞ B0 = β ⎜ ⎟ ⎝ dT ⎠

c (K·h−1)

T0 = 293.15 K

5 10 15 20 25

5.1 6.5 7.5 8.6 9.7

5 10 15 20 25

3.5 5.4 6.6 7.6 8.2

5 10 15 20 25

2.3 3.8 5.7 7.3 8

5 10 15 20 25

1.9 3.2 5.1 7.4 8.5

T0 = 303.15 K x3 = 0.0000 4.4 5.8 6.8 7.6 8.5 x3 = 0.2005 2.8 4.2 5.4 6.5 7.4 x3 = 0.4005 2 3.3 5.2 6.4 7.6 x3 = 0.6012 1.4 3 4.3 5.7 7.3

T0 = 313.15 K T0 = 323.15 K 2.4 4.2 5.5 6.5 7.6

1.4 2.7 4.2 5.9 6.8

2 3.6 5 6.2 6.8

1.2 2.4 3.8 5.4 6.2

1.5 2.8 4.3 5.2 6.2

1 2.1 3.8 4.6 5.1

1 2.2 3.8 5 5.9

0.9 2 3 4.4 5.3

a The standard uncertainties are u(T) = 0.05 K, u(P) = 0.005 MPa, u(ΔTmax) = 0.06 K.

⎛ dC ⎞ m − 1 β = k 0⎜ ⎟ (ΔTmax )m ⎝ dT ⎠

(9)

where β is the cooling rate, So eq 8 may be rewritten in the form: 310

(10)



Article

Figure 3. Plots of ln ΔTmax against ln β for pyridoxine hydrochloride at various saturation temperatures. Initial composition: (a) x3 = 0.0000; (b) x3 = 0.2005; (c) x3 = 0.4005; (d) x3 = 0.6012.

However, the MZW tends to decrease with increasing saturation temperature at a settled cooling rate. Probably because the viscosity of the solution is reduced, it can promote the burst nucleation. At constant temperature and a fixed cooling rate, the MZW becomes narrow with increasing the ethanol mole fraction of solvent mixtures. Therefore, a narrower MZW can be obtained by lower cooling rate, higher saturation temperature, and more ethanol in solvent mixtures, because the narrower MZW is more advantageous to produce tiny crystals in the crystallization process. As shown in Table 7 and Figure 3, it also shows that the presence of ethanol in solvents can affect the nucleation order. With the increasing of ethanol mole fraction, there are approximate parallel relationships for four fitted lines obtained by linear regression.

Taking logarithms on both sides of eq 10, upon rearrangement one obtains: ln ΔTmax =

1 − m ⎛⎜ dC ⎞⎟ 1 1 ln − ln k 0 + ln β ⎝ dT ⎠ m m m

(11)

Obviously eq 11 indicates a linear dependence of ln ΔTmax on ln β. In industrial crystallization, Nývlt’s equation is especially helpful for the crystal product and process optimization design. Unfortunately, the two parameters have complicated units, and their physical significance still remains obscure.18 The experimental data of MZW are listed in Table 6 and plotted in log−log coordinates in Figure 3. The values of nucleation order, m, obtained from the linear regression analysis (shown in Figure 3), was presented in Table 7 in detail. And the linear relationship between ln ΔTmax and ln β of pyridoxine hydrochloride at different saturation temperature is summarized in Table 7. And all results show a good linear relationship. As can be seen from Figure 3 and Table 6, in all temperatures under consideration, the MZW of pyridoxine hydrochloride increases with an increase of cooling rate.

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CONCLUSION In this paper, the solubility of pyridoxine hydrochloride in a binary system of water and ethanol solvent mixtures was measured using a laser method at the temperatures from (278.15 to 323.15) K and at mole fraction of ethanol from 0.0 311



Article

(5) Wang, L. H.; Cheng, Y. Y. Solubility of Puerarin in Water, Ethanol and Acetone from (288.2 to 328.2) K. J. Chem. Eng. Data 2005, 50, 1375−1376. (6) Li, X. N.; Yin, Q. X.; Chen, W.; Wang, J. K. Solubility of Hydroquinone in Different Solvents from 276.65 and 345.10 K. J. Chem. Eng. Data 2006, 51, 127−129. (7) Kulkarni, A. R.; Soppimath, K. S.; Aminabhavi, T. M. Solubility Study of Azadirachta indica A. Juss. (Neem) Seed Oil in the Presence of Cosolvent/ Nonionic Surfactant at (298.15, 303.15, 308.15, and 313.15) K. J. Chem. Eng. Data 1999, 44, 836−838. (8) Chen, Q. L.; Wang, Y. L.; Li, Y. B.; Wang, J. K. Solubility and Metastable Zone of Cefoperazone Sodium in Acetone + Water System. J. Chem. Eng. Data 2009, 54, 1123−1125. (9) Wang, L. P.; Peng, J. Y.; Li, L. L.; Feng, H. T.; Dong, Y. P.; Li, W.; Liang, J.; Zheng, Z. L. Solubility and Metastable Zone Width of Sodium Chromate Tetrahydrate. J. Chem. Eng. Data 2013, 58, 3165− 3169. (10) Ren, B. Z.; Yuan, X. L.; Li, C.; Zhao, H. K. Solubility of Tripolycyanamide and Cyanuric Acid in Ethanediol, N,N-Dimethylformamide, and N,N-Dimethylacetamide from (301.07 to 363.35) K. J. Chem. Eng. Data 2004, 49, 890−891. (11) Daneshfar, A.; Ghaziaskar, H. S.; Homayoun, N. Solubility of Gallic Acid in Methanol, Ethanol, Water, and Ethyl Acetate. J. Chem. Eng. Data 2008, 53, 757−758. (12) Wang, L. H.; Song, Y. T.; Chen, Y.; Cheng, Y. Y. Solubility of Artemisinin in Ethanol + Water from (278.2 to 343.2) K. J. Chem. Eng. Data 2007, 52, 757−758. (13) Kim, S. I.; Kim, C. U.; Park, S. J. Solubility, Density, and Metastable Zone Width of the (1, 4-Dioxan-2-one + Ethyl Acetate) System. J. Chem. Eng. Data 2005, 50, 1871−1874. (14) Nývlt, J.; Söhnel, O.; Matuchová, M.; Broul, M. The Kinetics of Industrial Crystallization; Elsevier: Amsterdam, 1985. (15) Nývlt, J. Kinetics of Nucleation in Solutions. J. Cryst. Growth 1968, 3−4, 377−383. (16) Wang, L. P.; Feng, H. T.; Peng, J. Y.; Dong, N. J.; Li, W.; Dong, Y. P. Solubility, Metastable Zone Width, and Nucleation Kinetics of Sodium Dichromate Dihydrate. J. Chem. Eng. Data 2015, 60, 185−191. (17) Mullin, J. W. Crystallization, 3rd ed.; Butterworth-Heinemann: London, 1993. (18) Zhang, X. Y.; Qian, G.; Zhou, X. G. Effects of Different Organic Acids on Solubility and Metastable Zone Width of Zinc Lactate. J. Chem. Eng. Data 2012, 57, 2963−2970.

Table 7. Nucleation Equation of Pyridoxine Hydrochloride in Water + Ethanol Solvents T0/K 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15 293.15 303.15 313.15 323.15

nucleation equation x3 = 0.0000 2.586 + 0.392 ln β 2.481 + 0.403 ln β 2.668 + 0.710 ln β 2.831 + 1.008 ln β x3 = 0.2005 ln ΔTmax = 2.607 + 0.533 ln β ln ΔTmax = 2.531 + 0.606 ln β ln ΔTmax = 2.653 + 0.778 ln β ln ΔTmax = 2.783 + 1.049 ln β x3 = 0.4005 ln ΔTmax = 2.827 + 0.806 ln β ln ΔTmax = 2.780 + 0.849 ln β ln ΔTmax = 2.636 + 0.892 ln β ln ΔTmax = 2.662 + 1.057 ln β x3 = 0.6012 ln ΔTmax = 2.991 + 0.966 ln β ln ΔTmax = 2.870 + 1.012 ln β ln ΔTmax = 2.829 + 1.131 ln β ln ΔTmax = 2.644 + 1.111 ln β ln ln ln ln

ΔTmax ΔTmax ΔTmax ΔTmax

= = = =

m

R2

2.551 2.481 1.408 0.992

0.991 0.999 0.995 0.997

1.876 1.650 1.285 0.953

0.991 0.999 0.993 0.996

1.241 1.178 1.121 0.946

0.993 0.994 0.996 0.981

1.035 0.988 0.884 0.900

0.988 0.998 0.994 0.998

to 0.6012. The density data was determined by using a U type vibrating-tube digital densimeter. All data are well-correlated by the empirical relationship described in this study. The solubility of pyridoxine hydrochloride in water and ethanol solvent mixtures shows a high dependence on ethanol mole fraction and dissolution temperature in the experimental temperature range from (278.15 to 323.15) K. The MZW of pyridoxine hydrochloride increases with the increasing cooling rate. But the MZW decreases with the increasing saturation temperatures and ethanol mole fraction. The nucleation equation was calculated by using Nývlt’s approach in this system. The experimental solubility, density, MZW data, and correlation equations in this study can be regarded as essential data and empirical models in the purification process of pyridoxine hydrochloride.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-28-84078939. Fax: +86-28-84079074. E-mail: [email protected]. Funding

The authors are grateful for financial support from the Foundation for Young Scholar of Chengdu University of Technology (KYGG201308). Notes

The authors declare no competing financial interest.

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REFERENCES

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Solubility, Density, and Metastable Zone Width of Pyridoxine

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