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Solubilities of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water from (292.65–361.35) K
Fluid Phase Equilibria 226 (2004) 289–293
Solubilities of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water from (292.65–361.35) K Liu-Cheng Wang∗ , Fu-An Wang College of Chemical Engineering, Zhengzhou University, Zhengzhou, Henan 450002, PR China Received 16 January 2004; accepted 11 June 2004 Available online 13 November 2004
Abstract Using a laser monitoring observation technique, the solubilities of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water have been determined experimentally from 292.65 to 361.35 K. The experimental data are correlated with the λh equation. The calculated results show good agreement with the experimental data. The fusion enthalpy of niacin was determined by using DSC. The excess enthalpy of solution HE is estimated for each system on the basis of the calculated parameter h and the measured enthalpy of fusion. © 2004 Published by Elsevier B.V. Keywords: Data; Solid–liquid equilibria; Excess enthalpy; Solubility; 3-Picoline; Sulfuric acid; Niacin
1. Introduction Niacin, also known as nicotinic acid or vitamin B5 , is an important drug, feed additive and intermediate with wide uses and optimum application prospects [1]. The authors [2] had developed a new technique for electrochemical synthesis of niacin using 3-picoline as raw material, a sulfuric acid aqueous solution as supporting electrolytes. This synthesis is characterized by mild reaction conditions, high product purity and reduced waste. In the synthesis and purification process of niacin, it is necessary to know the solubility data of niacin, but only solubility data of niacin in 3-picoline + water have been reported from 287.65 to 359.15 K [3,4]. In this work, the solubility of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water have been measured from 292.65 to 361.35 K at atmospheric pressure. Also, the solubility of niacin in 3-picoline + water is measured at mass fraction of 3-picoline in the solvent of 0.2 and 0.6, respectively, to complete the data reported in literature [4]. The experimental data were correlated with the λh equation [5,6]. The excess enthalpy (HE ) in the studied temperature range was estimated for each system on the basis of the calculated ∗
Corresponding author. Tel.: +86 371 3887327; fax: +86 371 3887327. E-mail address: [email protected] (L.-C. Wang).
0378-3812/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.fluid.2004.06.050
parameter h and the measured enthalpy of fusion (∆fus Hm ). The interactions between solute and solvent are discussed in Section 4 of this paper.
2. Experimental section 2.1. Materials High-grade sulfuric acid from Louyan Chemical Reagent Co. was used directly without further purification, and its purity was greater than 99% by mass. 3-Picoline obtained from Shanghai Chemical Reagent Co. was of AR grade, and was further purified by distillation; the purity was determined by UV spectrometry (type UV-2401PC, Shimadzu Co.), to be 99.7% by mass. Analytical grade nicotinic acid (niacin) obtained from Peking Biotech. Co. Ltd. was further purified by recrystallization from aqueous solutions. After filtration and drying, its purity was determined by titration to be 99.8% by mass. Water used in experiments was double distilled water. 2.2. Apparatus and procedure The solubility was measured by a dynamic method [7–9]. A laser monitoring observation technique [9,10] was used
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to determine the dissolution temperature of a solid–liquid mixture of known composition. The laser monitoring system consists of a laser, a photoelectric transformer, and a recorder. The experiments were carried out in a magnetically stirred, jacketed glass vessel (60 cm3 ). A constant temperature (±0.02 K) was maintained by circulating water through the outer jacket from a thermoelectric controller (type 501, Shanghai Laboratory Instrument Works Co. Ltd.) at the required temperature. A condenser was connected with the vessels to prevent the solvents from evaporating. A mercuryin-glass thermometer was inserted into the inner chamber of the vessels for the measurement of the temperature. The uncertainty of temperature was ±0.05 K. Solvents for the solubility measurements were prepared by mass using an electronic balance (type AW120, Shimadzu Co.). The balance has an accuracy of ±0.0001 g. Predetermined amounts of niacin were weighted and transferred into the vessel. The contents of the vessel were heated very slowly at rates less than 2 K h−1 under continuous stirring. To improve the accuracy of the experiments, the heating rate was controlled using a TP technique (temperature controller type AI-708P, Xiamen Electronic Technology Co. Ltd). In the early stages of the experiment, the laser beam was partly blocked by the unsolved particles of niacin in the solution, so the intensity of the laser beam penetrating the vessel was lower. The intensity increased gradually along increasing amount of niacin dissolved. When the last portion of niacin just disappeared, the intensity of the laser beam penetrating the vessel reached a maximum, and the temperature was recorded as the liquidus temperature. Each experimental data was replicated at least three times, the mean values were considered as the measured results. The accuracy of temperature measurements was 0.05 K. Reproducibility of measurements was 0.1 K, which corresponds to a relative error in composition smaller than 1%. Compared with the literature data [3] at 298.15 K, the deviation of solubility was less than 1%.
3. Results 3.1. Melting temperature and the fusion enthalpy of niacin The melting temperature (Tm = 509.25 K) and the fusion enthalpy (∆fus Hm = 97097 J mol−1 ) of niacin were determined by DSC (STA 449C, Germany NETZSCH Co.), the measured melting temperature show good agreement with the literature values (508.95–510.45 K) [11]. The measured accuracy of the Tm and ∆fus Hm are about ±1 K and ±5 J mol−1 , respectively. 3.2. Solubility data and correlation Measured mole fractions solubilities (x) of niacin in 3picoline + water, sulfuric acid + water and 3-picoline + sul-
Table 1 Solubility of niacin in sulfuric acid + water and excess enthalpy of solution: x experimental solubility; xc solubility calculated from Eq. (1); HE excess enthalpy estimated with Eq. (4) T (K)
x × 100
xc × 100
HE (J mol−1 )
10 wt.% Sulfuric acid + 90 wt.% water 295.95 6.209 309.45 6.609 315.15 6.783 319.35 6.946 324.15 7.125 329.15 7.336 333.15 7.557 339.35 7.828 345.15 8.158 350.45 8.439 358.15 8.964
6.144 6.592 6.800 6.960 7.153 7.364 7.541 7.831 8.121 8.403 8.846
1925.6 2049.7 2103.6 2154.2 2209.7 2275.1 2343.7 2427.7 2530.1 2617.2 2780.0
20 wt.% Sulfuric acid + 80 wt.% water 299.85 8.867 307.35 8.938 312.65 8.998 319.85 9.083 326.35 9.180 333.35 9.297 339.65 9.427 345.75 9.570 351.65 9.727 359.65 9.918
8.858 8.934 8.995 9.088 9.185 9.302 9.422 9.515 9.692 9.907
9509.4 9585.5 9649.8 9741.0 9845.0 9970.5 10110 10263 10432 10637
Table 2 Solubility of niacin in 3-picoline + water and excess enthalpy of solution: x experimental solubility; xc solubility calculated from Eq. (1); HE excess enthalpy estimated with Eq. (4) xc × 100
HE (J mol−1 )
20 wt.% 3-Picoline + 80 wt.% water 292.65 3.057 297.15 3.135 304.35 3.257 311.15 3.396 319.15 3.561 325.85 3.727 333.15 3.915 339.65 4.116 346.15 4.337 352.65 4.584 358.35 4.806
3.026 3.111 3.254 3.398 3.581 3.746 3.940 4.125 4.325 4.541 4.745
4075.8 4179.8 4342.4 4527.7 4747.7 4969.0 5219.7 5487.7 5782.3 6111.6 6407.6
60 wt.% 3-Picoline + 40 wt.% water 296.15 5.614 298.95 5.800 310.15 6.497 316.35 6.921 322.75 7.397 328.45 7.878 334.15 8.366 338.95 8.894 344.15 9.502 350.85 10.31 358.95 11.27
5.531 5.715 6.497 6.966 7.481 7.967 8.482 8.938 9.459 10.17 11.11
−2020.1 −2087.0 −2337.8 −2490.3 −2661.6 −2834.7 −-3010.3 −3200.3 −3419.1 −3659.4 −4055.2
T (K)
x × 100
furic acid + water at different temperatures are presented in Tables 1–3. The temperature dependence of niacin solubility at fixed solvent composition is described by the λh equation [5,6].
L.-C. Wang, F.-A. Wang / Fluid Phase Equilibria 226 (2004) 289–293 Table 3 Solubility of niacin in 3-picoline + sulfuric acid + water and excess enthalpy of solution: x experimental solubility; xc solubility calculated from Eq. (1); HE excess enthalpy estimated with Eq. (4) T (K)
x × 100
xc × 100
HE (J mol−1 )
291
the optimization technique, which minimizes the following objective function F: F=
N
(xci − xi )2
(2)
i=1
5 wt.% 3-picoline + 20 wt.% sulfuric acid + 75 wt.% water 296.35 4.131 4.095 304.95 4.220 4.200 311.35 4.291 4.286 316.95 4.367 4.368 322.65 4.451 4.457 328.15 4.535 4.550 332.35 4.623 4.626 337.25 4.714 4.720 341.65 4.816 4.809 346.15 4.923 4.907 351.15 5.056 5.022 360.55 5.340 5.263
8134.4 8309.6 8449.5 8599.1 8764.5 8929.9 9103.2 9282.4 9483.2 9693.9 9955.8 10515
10 wt.% 3-picoline + 20 wt.% sulfuric acid + 70 wt.% water 298.45 5.334 5.302 305.45 5.397 5.385 311.15 5.464 5.460 317.35 5.540 5.549 323.95 5.628 5.653 328.95 5.718 5.738 333.35 5.813 5.819 339.35 5.922 5.937 344.65 6.040 6.051 350.95 6.213 6.199 355.65 6.368 6.318 361.35 6.569 6.475
where, N is the number of experimental points and xci and xi refer to the solubility values calculated from Eq. (1) and to the experimental solubility. The calculated solubilities xc of the niacin using Eq. (1) are given in Tables 1–3. The values of the parameters λ and h are presented in Table 4. The calculated results show satisfactory agreement with the experimental data. The root-mean-square deviations (R.M.S.D.) are defined as: N 2 1/2 i=1 (xci − xi ) RMSD = (3) N
8856.6 8961.2 9072.5 9198.7 9344.8 9494.2 9652.0 9833.0 10029 10316 10573 10907
are presented in Table 4. The result shows that the λh equation can be used to correlate the solubilities data of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water.
4. Discussion and conclusion
15 wt.% 3-picoline + 20 wt.% sulfuric acid + 65 wt.% water 298.65 4.309 4.270 8708.1 307.15 4.385 4.370 8861.7 313.05 4.446 4.447 8984.9 318.25 4.515 4.521 9124.4 324.65 4.587 4.618 9269.9 328.65 4.659 4.684 9415.4 333.45 4.742 4.767 9583.1 337.65 4.830 4.845 9761.0 342.65 4.942 4.944 9987.3 348.25 5.089 5.063 10284 355.35 5.270 5.227 10650 358.85 5.386 5.316 10885
1−x ln 1 + λ x
= λh(T −1 − Tm−1 )
(1)
sat
Where, T is the absolute temperature and x is the solubility of niacin. Two adjustable parameters λ and h were obtained by
From the experimental data in Tables 1 and 2 and literature [4], it can be seen that the solubility of niacin in water is much lower than in 3-picoline and sulfuric acid + water, and the solubility of niacin in sulfuric acid + water is higher than in 3-picoline + water. For 3-picoline + water and sulfuric acid + water binary solvents, the solubility of niacin decreases with increasing concentration of water, and the solubility increases with increasing concentration of sulfuric acid or 3-picoline. Under the same mass fraction, the increment of solubility caused by sulfuric acid is higher than by 3picoline. According to Scatchard–Hildebrand’s theory [12,13], the solubility of solute in the solvent is the largest when solubility parameter of solute and solvent are same. When solubility parameter (δ1 ) of solute and solubility parameter (δA , δB ) of solvents follows the condition: δA <δ1 <δB , the system probably reveal synergistic effect for A + B binary solvents systems. The values of the solubility parameter of niacin, δ1 = 24.4 MPa1/2 , was calculated by the Scatchard’s group
Table 4 Parameters in the λh equation for different systems Solvents
λ × 100
h
RMSD × 104
10 wt.% sulfuric acid + 90 wt.% water 20 wt.% sulfuric acid + 80 wt.% water 20 wt.% 3-picoline + 80 wt.% water 60 wt.% 3-picoline + 40 wt.% water 5 wt.% 3-picoline + 20 wt.% sulfuric acid + 75 wt.% water 10 wt.% 3-picoline + 20 wt.% sulfuric acid + 70 wt.% water 15 wt.% 3-picoline + 20 wt.% sulfuric acid + 65 wt.% water
−3.485 −9.295 −1.183 8.896 −3.539 −4.966 −3.783
15409 24578 27715 7350.8 35363 31650 35986
4.6 2.1 2.8 9.2 2.8 3.4 3.1
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contribution method [13]. Solubility parameters for 3picoline (δ = 20.9 MPa1/2 ) and water (δ = 47.9 MPa1/2 ), come from CRC handbook [13], and for sulfuric acid (δ = 29.8 MPa1/2 ) was calculated through vaporization enthalpy [14] basing to its definition. From the values of solubility parameters, it can be predicted that niacin with sulfuric acid (A) + water (B) binary solvents won’t reveal synergistic effect, whereas with 3-picoline (A) + water (B) binary solvents probably exhibit a synergistic effect on solubility. For discussion, the T x curves for niacin + 3-picoline + water system are given in Fig. 1, by using eight sets of experimental data from Table 2 and literature [4]. However, the synergistic effect are not observed except the case of a large mass fraction (w = 0.6) of 3-picoline in the solvent at low temperature, probably due to the very small solubility of niacin in pure water and, thus, the larger difference in solubilities of niacin in pure 3picoline. For further investigation, the solubilities of niacin at 283.15 and 303.15 K were calculated from Eq. (1) and values of λ and h. The dependence of the solubilities x on mass fraction w of 3-picoline in solvent is presented in Fig. 2. At w ≈ 0.6, obviously, the curves have inflection points, and the curve has a maximum value for 283.15 K. In the range of w close to 1, the phenomenon of the solubility increasing probably due to the structural similarity of molecules of niacin and 3-picoline, especially to the special interactions between acidic groups of niacin molecule and weakly alkaline groups of 3-picoline molecule. For niacin + 3-picoline + sulfuric acid + water systems, the plots of solubility x against temperature T were given in Fig. 3 by using the three sets of experimental data from Table 3. From figure we can observe the obvious synergistic effect on solubility. This synergistic effect probably is due to the intermolecular interactions between four kinds of different molecules, a complicated problem in itself.
Fig. 1. Solubilities x of niacin in various concentrations of 3-picoline + water at different temperatures T: (1) water; (2) 5 wt.% 3-picoline; (3) 10 wt.% 3-picoline; (4) 20 wt.% 3-picoline; (5) 40 wt.% 3-picoline; (6) 60 wt.% 3picoline; (7) 80 wt.% 3-picoline, and; (8) 3-picoline. Points are experimental data and solid lines are the plots of Eq. (1).
Fig. 2. The dependence of the solubilities x calculated from Eq. (1) and values of λ and h at 283.15 and 303.15 K on mass fraction w of 3-picoline in solvent for niacin +3-picoline + water systems.
In the λh equation, the parameter h is related to the enthalpy of solution per mole of solute. The expression due to Buchowski et al. [5] is given in Eq. (4), where HE is the excess enthalpy of the solution. Eq. (4) may be used to estimate the values of HE in order to have a more detailed understanding of solution characteristics, and the estimated values of HE are also shown in Tables 1–3 for every system. HE (4) x From Table 2, we can find that the excess enthalpies for 20 wt.% 3-picoline + 80 wt.% water system are positive, but for 60 wt.% 3-picoline + 40 wt.% water system are negative. In order to discuss this special phenomenon in niacin + 3picoline (A) + water (B) systems, using the experimental data of Table 2 and literature [4], the excess enthalpies at 303.15 K were estimated from Eqs. (1) and (4). The dependence of the excess enthalpies HE on mole fraction xA of 3-picoline in solutions is presented in Fig. 4. At xA = 0, the excess enthalpies are close to 0, probably due to the very small solubility of niacin in pure water, the solution similar to pure water. hR = ∆fus Hm +
Fig. 3. Solubilities x of niacin in various concentrations of 3-picoline + sulfuric acid + water at different temperatures T. Mixed solvent systems containing 20 wt.% H2 SO4 and (1) 5 wt.% 3-picoline; (2) 10 wt.% 3-picoline, and; (3) 15 wt.% 3-picoline. Points are experimental data and solid lines are the plots of Eq. (1).
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293
List of Symbols
Fig. 4. The dependence of the excess enthalpies HE estimated from Eqs. (1) and (4) at 303.15 K on mole fraction xA of 3-picoline in solutions for niacin +3-picoline + water systems.
With the increasing values of xA , the concentration of 3picoline increase, the neighboring 3-picoline molecules are associated through hydrogen bonding between the nitrogen and the carbon atoms of the ring: C–H...N, except for the association of water molecules. In the range of xA < 0.17, the contents of niacin in the solution is lower, its effect on excess enthalpy is also weaker, the breakdown of AA 3picoline association and BB water association play a predominant role. The mixtures display positive HE values indicating that the AB interactions are weaker than the AA or BB interactions. With the further increasing concentration of 3-picoline, the 3-picoline display weakly alkalinity gradually, the chemical interaction will occur between acidic groups of niacin molecule and weakly alkaline groups of 3-picoline molecule. The chemical thermal effect can gradually reduce the contribution to HE from breakdown of AA and BB bonds, and leads to release heat, therefore, in the range of xA > 0.17, the HE < 0. For niacin + sulfuric acid + water ternary systems and niacin + 3-picoline + sulfuric acid + water quaternary systems, the values of excess enthalpy are positive mainly resulting from the breakdown of association bonds.
HE h N R T Tm w x xc xA δ λ fus Hm
excess enthalpy estimated with Eq. (4) parameter of Eq. (1) number of experimental points gas constant absolute temperature melting temperature mass fraction of 3-picoline in the solvent mole fraction experimental solubility mole fraction solubility calculated from Eq. (1) mole fraction of 3-picoline in solutions solubility parameter parameter of Eq. (1) enthalpy of fusion
References [1] P.M. Guiot, A. Ryan, E.F.V. Scriven, Chim. Oggi. 14 (1996) 55–57. [2] L.-C. Wang, F.–A. Wang, 12th National Conference on Electrochemistry, Shanghai, China, 18–19 November 2003, p. B04. [3] Jr. Toomey, Electrochemical Synthesis of Niacin and other NHeterocyclic Compounds, US Patent 5002641 (1991). [4] L.-C. Wang, F.-A. Wang, J. Chem. Eng. Data 49 (2004) 155–156. [5] H. Buchowski, A. Ksiazczak, S. Pietrzyk, J. Phys. Chem. 84 (1980) 975–979. [6] U. Domanska, Fluid Phase Equilib. 26 (1986) 201–220. [7] U. Domanska, M.K. Kozlowska, Fluid Phase Equilib. 206 (2003) 253–266. [8] U. Domanska, M.A. Pobudkowska, Fluid Phase Equilib. 206 (2003) 341–353. [9] D.-Q. Li, J.-C. Liu, D.-Z. Liu, F.-A. Wang, Fluid Phase Equilib. 200 (2002) 69–74. [10] D.-Q. Li, D.-Z. Liu, F.-A. Wang, J. Chem. Eng. Data 46 (2001) 172–173. [11] E.M. Alkaeva, T.V. Andrushkevich, Method of Obtaining Nicotinic Acid, US Patent 5728837 (1998). [12] J.M. Prausnitz, R.N. Lichtenthaler, E.G. Azevedo, Molecular Thermodynamics of Fluid–Phase Equilibria, third ed., Prentice-Hall PTR, Upper Saddle River, New Jersey, 1999. [13] A.F.M. Barton, CRC Handbook of Solubility Parameters and Other Cohesion Parameters, second ed., CRC Press, Floride, 1991. [14] J.A. Dean, Lange’s Handbook of Chemistry, 15th ed., McGraw-Hill Book Co., 1999.
Solubilities of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water from (292.65–361.35) K Liu-Cheng Wang∗ , Fu-An Wang College of Chemical Engineering, Zhengzhou University, Zhengzhou, Henan 450002, PR China Received 16 January 2004; accepted 11 June 2004 Available online 13 November 2004
Abstract Using a laser monitoring observation technique, the solubilities of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water have been determined experimentally from 292.65 to 361.35 K. The experimental data are correlated with the λh equation. The calculated results show good agreement with the experimental data. The fusion enthalpy of niacin was determined by using DSC. The excess enthalpy of solution HE is estimated for each system on the basis of the calculated parameter h and the measured enthalpy of fusion. © 2004 Published by Elsevier B.V. Keywords: Data; Solid–liquid equilibria; Excess enthalpy; Solubility; 3-Picoline; Sulfuric acid; Niacin
1. Introduction Niacin, also known as nicotinic acid or vitamin B5 , is an important drug, feed additive and intermediate with wide uses and optimum application prospects [1]. The authors [2] had developed a new technique for electrochemical synthesis of niacin using 3-picoline as raw material, a sulfuric acid aqueous solution as supporting electrolytes. This synthesis is characterized by mild reaction conditions, high product purity and reduced waste. In the synthesis and purification process of niacin, it is necessary to know the solubility data of niacin, but only solubility data of niacin in 3-picoline + water have been reported from 287.65 to 359.15 K [3,4]. In this work, the solubility of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water have been measured from 292.65 to 361.35 K at atmospheric pressure. Also, the solubility of niacin in 3-picoline + water is measured at mass fraction of 3-picoline in the solvent of 0.2 and 0.6, respectively, to complete the data reported in literature [4]. The experimental data were correlated with the λh equation [5,6]. The excess enthalpy (HE ) in the studied temperature range was estimated for each system on the basis of the calculated ∗
Corresponding author. Tel.: +86 371 3887327; fax: +86 371 3887327. E-mail address: [email protected] (L.-C. Wang).
0378-3812/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.fluid.2004.06.050
parameter h and the measured enthalpy of fusion (∆fus Hm ). The interactions between solute and solvent are discussed in Section 4 of this paper.
2. Experimental section 2.1. Materials High-grade sulfuric acid from Louyan Chemical Reagent Co. was used directly without further purification, and its purity was greater than 99% by mass. 3-Picoline obtained from Shanghai Chemical Reagent Co. was of AR grade, and was further purified by distillation; the purity was determined by UV spectrometry (type UV-2401PC, Shimadzu Co.), to be 99.7% by mass. Analytical grade nicotinic acid (niacin) obtained from Peking Biotech. Co. Ltd. was further purified by recrystallization from aqueous solutions. After filtration and drying, its purity was determined by titration to be 99.8% by mass. Water used in experiments was double distilled water. 2.2. Apparatus and procedure The solubility was measured by a dynamic method [7–9]. A laser monitoring observation technique [9,10] was used
290
L.-C. Wang, F.-A. Wang / Fluid Phase Equilibria 226 (2004) 289–293
to determine the dissolution temperature of a solid–liquid mixture of known composition. The laser monitoring system consists of a laser, a photoelectric transformer, and a recorder. The experiments were carried out in a magnetically stirred, jacketed glass vessel (60 cm3 ). A constant temperature (±0.02 K) was maintained by circulating water through the outer jacket from a thermoelectric controller (type 501, Shanghai Laboratory Instrument Works Co. Ltd.) at the required temperature. A condenser was connected with the vessels to prevent the solvents from evaporating. A mercuryin-glass thermometer was inserted into the inner chamber of the vessels for the measurement of the temperature. The uncertainty of temperature was ±0.05 K. Solvents for the solubility measurements were prepared by mass using an electronic balance (type AW120, Shimadzu Co.). The balance has an accuracy of ±0.0001 g. Predetermined amounts of niacin were weighted and transferred into the vessel. The contents of the vessel were heated very slowly at rates less than 2 K h−1 under continuous stirring. To improve the accuracy of the experiments, the heating rate was controlled using a TP technique (temperature controller type AI-708P, Xiamen Electronic Technology Co. Ltd). In the early stages of the experiment, the laser beam was partly blocked by the unsolved particles of niacin in the solution, so the intensity of the laser beam penetrating the vessel was lower. The intensity increased gradually along increasing amount of niacin dissolved. When the last portion of niacin just disappeared, the intensity of the laser beam penetrating the vessel reached a maximum, and the temperature was recorded as the liquidus temperature. Each experimental data was replicated at least three times, the mean values were considered as the measured results. The accuracy of temperature measurements was 0.05 K. Reproducibility of measurements was 0.1 K, which corresponds to a relative error in composition smaller than 1%. Compared with the literature data [3] at 298.15 K, the deviation of solubility was less than 1%.
3. Results 3.1. Melting temperature and the fusion enthalpy of niacin The melting temperature (Tm = 509.25 K) and the fusion enthalpy (∆fus Hm = 97097 J mol−1 ) of niacin were determined by DSC (STA 449C, Germany NETZSCH Co.), the measured melting temperature show good agreement with the literature values (508.95–510.45 K) [11]. The measured accuracy of the Tm and ∆fus Hm are about ±1 K and ±5 J mol−1 , respectively. 3.2. Solubility data and correlation Measured mole fractions solubilities (x) of niacin in 3picoline + water, sulfuric acid + water and 3-picoline + sul-
Table 1 Solubility of niacin in sulfuric acid + water and excess enthalpy of solution: x experimental solubility; xc solubility calculated from Eq. (1); HE excess enthalpy estimated with Eq. (4) T (K)
x × 100
xc × 100
HE (J mol−1 )
10 wt.% Sulfuric acid + 90 wt.% water 295.95 6.209 309.45 6.609 315.15 6.783 319.35 6.946 324.15 7.125 329.15 7.336 333.15 7.557 339.35 7.828 345.15 8.158 350.45 8.439 358.15 8.964
6.144 6.592 6.800 6.960 7.153 7.364 7.541 7.831 8.121 8.403 8.846
1925.6 2049.7 2103.6 2154.2 2209.7 2275.1 2343.7 2427.7 2530.1 2617.2 2780.0
20 wt.% Sulfuric acid + 80 wt.% water 299.85 8.867 307.35 8.938 312.65 8.998 319.85 9.083 326.35 9.180 333.35 9.297 339.65 9.427 345.75 9.570 351.65 9.727 359.65 9.918
8.858 8.934 8.995 9.088 9.185 9.302 9.422 9.515 9.692 9.907
9509.4 9585.5 9649.8 9741.0 9845.0 9970.5 10110 10263 10432 10637
Table 2 Solubility of niacin in 3-picoline + water and excess enthalpy of solution: x experimental solubility; xc solubility calculated from Eq. (1); HE excess enthalpy estimated with Eq. (4) xc × 100
HE (J mol−1 )
20 wt.% 3-Picoline + 80 wt.% water 292.65 3.057 297.15 3.135 304.35 3.257 311.15 3.396 319.15 3.561 325.85 3.727 333.15 3.915 339.65 4.116 346.15 4.337 352.65 4.584 358.35 4.806
3.026 3.111 3.254 3.398 3.581 3.746 3.940 4.125 4.325 4.541 4.745
4075.8 4179.8 4342.4 4527.7 4747.7 4969.0 5219.7 5487.7 5782.3 6111.6 6407.6
60 wt.% 3-Picoline + 40 wt.% water 296.15 5.614 298.95 5.800 310.15 6.497 316.35 6.921 322.75 7.397 328.45 7.878 334.15 8.366 338.95 8.894 344.15 9.502 350.85 10.31 358.95 11.27
5.531 5.715 6.497 6.966 7.481 7.967 8.482 8.938 9.459 10.17 11.11
−2020.1 −2087.0 −2337.8 −2490.3 −2661.6 −2834.7 −-3010.3 −3200.3 −3419.1 −3659.4 −4055.2
T (K)
x × 100
furic acid + water at different temperatures are presented in Tables 1–3. The temperature dependence of niacin solubility at fixed solvent composition is described by the λh equation [5,6].
L.-C. Wang, F.-A. Wang / Fluid Phase Equilibria 226 (2004) 289–293 Table 3 Solubility of niacin in 3-picoline + sulfuric acid + water and excess enthalpy of solution: x experimental solubility; xc solubility calculated from Eq. (1); HE excess enthalpy estimated with Eq. (4) T (K)
x × 100
xc × 100
HE (J mol−1 )
291
the optimization technique, which minimizes the following objective function F: F=
N
(xci − xi )2
(2)
i=1
5 wt.% 3-picoline + 20 wt.% sulfuric acid + 75 wt.% water 296.35 4.131 4.095 304.95 4.220 4.200 311.35 4.291 4.286 316.95 4.367 4.368 322.65 4.451 4.457 328.15 4.535 4.550 332.35 4.623 4.626 337.25 4.714 4.720 341.65 4.816 4.809 346.15 4.923 4.907 351.15 5.056 5.022 360.55 5.340 5.263
8134.4 8309.6 8449.5 8599.1 8764.5 8929.9 9103.2 9282.4 9483.2 9693.9 9955.8 10515
10 wt.% 3-picoline + 20 wt.% sulfuric acid + 70 wt.% water 298.45 5.334 5.302 305.45 5.397 5.385 311.15 5.464 5.460 317.35 5.540 5.549 323.95 5.628 5.653 328.95 5.718 5.738 333.35 5.813 5.819 339.35 5.922 5.937 344.65 6.040 6.051 350.95 6.213 6.199 355.65 6.368 6.318 361.35 6.569 6.475
where, N is the number of experimental points and xci and xi refer to the solubility values calculated from Eq. (1) and to the experimental solubility. The calculated solubilities xc of the niacin using Eq. (1) are given in Tables 1–3. The values of the parameters λ and h are presented in Table 4. The calculated results show satisfactory agreement with the experimental data. The root-mean-square deviations (R.M.S.D.) are defined as: N 2 1/2 i=1 (xci − xi ) RMSD = (3) N
8856.6 8961.2 9072.5 9198.7 9344.8 9494.2 9652.0 9833.0 10029 10316 10573 10907
are presented in Table 4. The result shows that the λh equation can be used to correlate the solubilities data of niacin in sulfuric acid + water and 3-picoline + sulfuric acid + water.
4. Discussion and conclusion
15 wt.% 3-picoline + 20 wt.% sulfuric acid + 65 wt.% water 298.65 4.309 4.270 8708.1 307.15 4.385 4.370 8861.7 313.05 4.446 4.447 8984.9 318.25 4.515 4.521 9124.4 324.65 4.587 4.618 9269.9 328.65 4.659 4.684 9415.4 333.45 4.742 4.767 9583.1 337.65 4.830 4.845 9761.0 342.65 4.942 4.944 9987.3 348.25 5.089 5.063 10284 355.35 5.270 5.227 10650 358.85 5.386 5.316 10885
1−x ln 1 + λ x
= λh(T −1 − Tm−1 )
(1)
sat
Where, T is the absolute temperature and x is the solubility of niacin. Two adjustable parameters λ and h were obtained by
From the experimental data in Tables 1 and 2 and literature [4], it can be seen that the solubility of niacin in water is much lower than in 3-picoline and sulfuric acid + water, and the solubility of niacin in sulfuric acid + water is higher than in 3-picoline + water. For 3-picoline + water and sulfuric acid + water binary solvents, the solubility of niacin decreases with increasing concentration of water, and the solubility increases with increasing concentration of sulfuric acid or 3-picoline. Under the same mass fraction, the increment of solubility caused by sulfuric acid is higher than by 3picoline. According to Scatchard–Hildebrand’s theory [12,13], the solubility of solute in the solvent is the largest when solubility parameter of solute and solvent are same. When solubility parameter (δ1 ) of solute and solubility parameter (δA , δB ) of solvents follows the condition: δA <δ1 <δB , the system probably reveal synergistic effect for A + B binary solvents systems. The values of the solubility parameter of niacin, δ1 = 24.4 MPa1/2 , was calculated by the Scatchard’s group
Table 4 Parameters in the λh equation for different systems Solvents
λ × 100
h
RMSD × 104
10 wt.% sulfuric acid + 90 wt.% water 20 wt.% sulfuric acid + 80 wt.% water 20 wt.% 3-picoline + 80 wt.% water 60 wt.% 3-picoline + 40 wt.% water 5 wt.% 3-picoline + 20 wt.% sulfuric acid + 75 wt.% water 10 wt.% 3-picoline + 20 wt.% sulfuric acid + 70 wt.% water 15 wt.% 3-picoline + 20 wt.% sulfuric acid + 65 wt.% water
−3.485 −9.295 −1.183 8.896 −3.539 −4.966 −3.783
15409 24578 27715 7350.8 35363 31650 35986
4.6 2.1 2.8 9.2 2.8 3.4 3.1
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contribution method [13]. Solubility parameters for 3picoline (δ = 20.9 MPa1/2 ) and water (δ = 47.9 MPa1/2 ), come from CRC handbook [13], and for sulfuric acid (δ = 29.8 MPa1/2 ) was calculated through vaporization enthalpy [14] basing to its definition. From the values of solubility parameters, it can be predicted that niacin with sulfuric acid (A) + water (B) binary solvents won’t reveal synergistic effect, whereas with 3-picoline (A) + water (B) binary solvents probably exhibit a synergistic effect on solubility. For discussion, the T x curves for niacin + 3-picoline + water system are given in Fig. 1, by using eight sets of experimental data from Table 2 and literature [4]. However, the synergistic effect are not observed except the case of a large mass fraction (w = 0.6) of 3-picoline in the solvent at low temperature, probably due to the very small solubility of niacin in pure water and, thus, the larger difference in solubilities of niacin in pure 3picoline. For further investigation, the solubilities of niacin at 283.15 and 303.15 K were calculated from Eq. (1) and values of λ and h. The dependence of the solubilities x on mass fraction w of 3-picoline in solvent is presented in Fig. 2. At w ≈ 0.6, obviously, the curves have inflection points, and the curve has a maximum value for 283.15 K. In the range of w close to 1, the phenomenon of the solubility increasing probably due to the structural similarity of molecules of niacin and 3-picoline, especially to the special interactions between acidic groups of niacin molecule and weakly alkaline groups of 3-picoline molecule. For niacin + 3-picoline + sulfuric acid + water systems, the plots of solubility x against temperature T were given in Fig. 3 by using the three sets of experimental data from Table 3. From figure we can observe the obvious synergistic effect on solubility. This synergistic effect probably is due to the intermolecular interactions between four kinds of different molecules, a complicated problem in itself.
Fig. 1. Solubilities x of niacin in various concentrations of 3-picoline + water at different temperatures T: (1) water; (2) 5 wt.% 3-picoline; (3) 10 wt.% 3-picoline; (4) 20 wt.% 3-picoline; (5) 40 wt.% 3-picoline; (6) 60 wt.% 3picoline; (7) 80 wt.% 3-picoline, and; (8) 3-picoline. Points are experimental data and solid lines are the plots of Eq. (1).
Fig. 2. The dependence of the solubilities x calculated from Eq. (1) and values of λ and h at 283.15 and 303.15 K on mass fraction w of 3-picoline in solvent for niacin +3-picoline + water systems.
In the λh equation, the parameter h is related to the enthalpy of solution per mole of solute. The expression due to Buchowski et al. [5] is given in Eq. (4), where HE is the excess enthalpy of the solution. Eq. (4) may be used to estimate the values of HE in order to have a more detailed understanding of solution characteristics, and the estimated values of HE are also shown in Tables 1–3 for every system. HE (4) x From Table 2, we can find that the excess enthalpies for 20 wt.% 3-picoline + 80 wt.% water system are positive, but for 60 wt.% 3-picoline + 40 wt.% water system are negative. In order to discuss this special phenomenon in niacin + 3picoline (A) + water (B) systems, using the experimental data of Table 2 and literature [4], the excess enthalpies at 303.15 K were estimated from Eqs. (1) and (4). The dependence of the excess enthalpies HE on mole fraction xA of 3-picoline in solutions is presented in Fig. 4. At xA = 0, the excess enthalpies are close to 0, probably due to the very small solubility of niacin in pure water, the solution similar to pure water. hR = ∆fus Hm +
Fig. 3. Solubilities x of niacin in various concentrations of 3-picoline + sulfuric acid + water at different temperatures T. Mixed solvent systems containing 20 wt.% H2 SO4 and (1) 5 wt.% 3-picoline; (2) 10 wt.% 3-picoline, and; (3) 15 wt.% 3-picoline. Points are experimental data and solid lines are the plots of Eq. (1).
L.-C. Wang, F.-A. Wang / Fluid Phase Equilibria 226 (2004) 289–293
293
List of Symbols
Fig. 4. The dependence of the excess enthalpies HE estimated from Eqs. (1) and (4) at 303.15 K on mole fraction xA of 3-picoline in solutions for niacin +3-picoline + water systems.
With the increasing values of xA , the concentration of 3picoline increase, the neighboring 3-picoline molecules are associated through hydrogen bonding between the nitrogen and the carbon atoms of the ring: C–H...N, except for the association of water molecules. In the range of xA < 0.17, the contents of niacin in the solution is lower, its effect on excess enthalpy is also weaker, the breakdown of AA 3picoline association and BB water association play a predominant role. The mixtures display positive HE values indicating that the AB interactions are weaker than the AA or BB interactions. With the further increasing concentration of 3-picoline, the 3-picoline display weakly alkalinity gradually, the chemical interaction will occur between acidic groups of niacin molecule and weakly alkaline groups of 3-picoline molecule. The chemical thermal effect can gradually reduce the contribution to HE from breakdown of AA and BB bonds, and leads to release heat, therefore, in the range of xA > 0.17, the HE < 0. For niacin + sulfuric acid + water ternary systems and niacin + 3-picoline + sulfuric acid + water quaternary systems, the values of excess enthalpy are positive mainly resulting from the breakdown of association bonds.
HE h N R T Tm w x xc xA δ λ fus Hm
excess enthalpy estimated with Eq. (4) parameter of Eq. (1) number of experimental points gas constant absolute temperature melting temperature mass fraction of 3-picoline in the solvent mole fraction experimental solubility mole fraction solubility calculated from Eq. (1) mole fraction of 3-picoline in solutions solubility parameter parameter of Eq. (1) enthalpy of fusion
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