Solubility of Benzoic Acid and Aspirin in Pure Solvents Using Focused

Dec 23, 2015 - (1-3) The literature for the solubility of benzoic acid covers a wide range ... per second of chord lengths in the size range of 1–10...
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Solubility of Benzoic Acid and Aspirin in Pure Solvents Using Focused Beam Reflective Measurement Gavin Tully,† Guangyang Hou,† and Brian Glennon*,† †

Solid State Pharmaceutical Cluster, School of Chemical and Bioprocess Engineering, University College Dublin, Belfield Dublin 4, Ireland ABSTRACT: The solubility of benzoic acid and acetylsalicylic acid is reported in varied pure solvents over a range of 275.39−327.03 K and 275.12−327.91 K for benzoic acid and aspirin, respectively, using the polythermal method with a heating rate of 0.1 K/min that was combined with the Lasentec focused beam reflective measurement to determine the saturation point of the solutions. The results were correlated using a modified van’t Hoff equation that fitted the solubility with a 2 K interval over a temperature range of 278.15− 323.15 K. The results from the fitting equation were in good agreement with the experimental data.

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INTRODUCTION Crystallization is a widely used purification and separation step for the manufacturing of crystalline material in the pharmaceutical, food, and chemical sectors. Knowledge of the solubility of a solute in a given solvent or solvent mixture is important in the design of suitable crystallization strategies. Benzoic acid, the simplest carboxylic acid, is a widely available intermediate compound that has many applications in the production of pharmaceuticals, chemicals, and food that can be produced through different techniques such as cooling, antisolvent, and continuous crystallization.1−3 The literature for the solubility of benzoic acid covers a wide range of pure solvents and mixed solvents systems with several studies of mixed solvent data being in aqueous-solvent mixtures.4−10 The solubility of benzoic acid has been reported in single solvent systems with examples such as acetone, 2-propanol, acetic acid, cyclohexane, isobutyl acetate, and ethanol.4,7,9 The purpose of this study is to investigate further the effect of temperature on the solubility in a wider range of pure solvents covering the alcohol, ketone, and acetate functional groups. Aspirin (acetylsalicylic acid) is a widely available over the counter drug as it is an analgesic (pain reliever) and antipyretic (fever reducer) that also has anti-inflammatory properties. The solubility of aspirin has been collected in pure and mixed solvent systems across multiple cases in the literature.10−16 The objective of this study is to investigate further the effect of temperature on the solubility in a wider range of pure solvents covering the alcohol, acetate, and ketone functional groups. The chemical structures of benzoic acid and aspirin are shown in Figure 1. The polythermal method,17 which has been used to accurately determined the metastable zone width in wide range of systems including glycine in water and prednisone acetate in a range of solvents,18−20 was utilized to measure the solubility of benzoic acid and aspirin in this work. The van’t Hoff equation, which has been demonstrated to provide an © XXXX American Chemical Society

Figure 1. Chemical structure of (A) benzoic acid and (B) aspirin.

effective correlation of the solubility data for benzoic acid in four pure solvents4 and salicylic acid in a range of pure solvents and binary solvent mixtures,21 was employed to correlate the experimental results in this work.

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EXPERIMENTAL SECTION Materials. The materials evaluated in this study with corresponding sources, purity (determined by chemical supplier) and analysis method are shown in Table 1. Methods. The Mettler Toledo EasyMax system was used in conjunction with the Lasentec focused beam reflective measurement (FBRM) to determine the saturation point of the solutions of interest. The EasyMax system has two independently controlled reactors which have an operating range of 20−120 mL. The system has a Peltier heating/cooling system that allows for an operational temperature range of 233.15−453.15 K with the temperature measured to within 0.01 K. The heating rate used for dissolution detection is 0.1 K/ min, which has been previously shown to be suitable for similar solubility studies.18,22 The reactors were agitated with an overhead mechanical stirrer with a downward pumping pitched blade impeller. Each reactor was fitted with a condenser and all ports tightly sealed to avoid evaporative loss of solvent. The weight of the solute and solvent was measured on an Ohaus Pioneer balance with a standard uncertainty of 0.001 g. Received: September 2, 2015 Accepted: December 16, 2015

A

DOI: 10.1021/acs.jced.5b00746 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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where the evolution of the trends with respect to experiment time are tracked with changing temperature in terms of counts per second of chord lengths in the size range of 1−1000 μm and the coarse counts/#·s−1 in the size range of 50−250 μm.

Table 1. Sources and Mass Fraction Purity of Materials with Corresponding Analysis Method chemical name benzoic acid

source

SigmaAldrich aspirin SigmaAldrich methanol SigmaAldrich 1-propanol SigmaAldrich 1-butanol SigmaAldrich isobutanol Acros Organics ethyl acetate Fischer Scientific isopropyl acetate Fischer Scientific isobutyl acetate SigmaAldrich methyl ethyl ketone Fluka (MEK) methyl isobutyl Sigmaketone (MIBK) Aldrich

mass fraction purity

further purification method

analysis method

99.5%

none

HPLC

≥ 99%

none

HPLC

≥ 99.8%

none

HPLC

≥ 99.5%

none

HPLC

≥ 99.5%

none

HPLC

≥ 99%

none

HPLC

≥ 99%

none

HPLC

≥ 98%

none

HPLC

≥ 99%

none

HPLC

≥ 99.5%

none

HPLC

≥ 99%

none

HPLC

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RESULTS AND DISCUSSION The solubility temperature data for the benzoic acid and aspirin in terms of a concentration ratio (CR), a ratio on a mass basis of gram of solute per gram of solvent, in the different solvents investigated are displayed in Tables 2 and 3, respectively. The temperature dependence of the mole fraction solubility for benzoic acid and aspirin in the varied solvents is described by the modified three parameter van’t Hoff expression (eq 1)21,25 ln xf = A +

B C + 2 T T

(1)

where xf is the solubility mole fraction of benzoic acid; T is the absolute temperature in K; A, B, and C are model parameters regressed from experimental data. The root-mean-square deviation (RMSD) between the experimental data and the fitted solubility data from eq 1 is calculated using eq 220,26,27 ⎡1 RMSD = ⎢ ⎢⎣ N

The solubility was measured by implementation of the polythermal method17,18,20 with the FBRM probe to determine the saturation point of the solution, as previously described in the literature.22−24 FBRM probe tracks the present of a solid phase via the detection of reflection of a scanning laser beam focused in the suspension. The number and size of particles present are reported in terms of the number of counts (#·s−1) of chord lengths of the detected particles, which can be classified into categories of specified size ranges, during both heating and cooling cycles. Previous research has demonstrated the suitability of the FBRM probe for determining the saturation point by tracking the counts of particles in the coarse range of 50−250 μm and the total counts in the size range of 1−1000 μm.22,24 The heating rate utilized for dissolution detection is 0.1 K/min, which was shown to be suitable for similar studies.22,24 A standard cooling rate of 0.5 K was also applied. An example of the FBRM trends obtained during the determination of the saturation point is illustrated in Figure 2,

n

⎤1/2

2⎥

∑ (xf − xi) i=1

⎥⎦

(2)

where N is the number of solubility points; xf is the solubility mole fraction calculated from eq 1; xi is the experimentally measured solubility mole fraction. The relative deviation percentage (RD%)20,26,27 and percentage relative average deviation percentage (RAD%)20,28 of the fitted solubility data are defined as RD% =

(xi − xf ) × 100 xi

RAD% =

1 N

N

∑ i=1

(3)

xi − xf × 100 xi

(4)

The accuracy of the fitted results from eq 1 were evaluated using eqs 2−4, which are listed in Tables 4 and 5 for benzoic acid and aspirin, respectively, that illustrate a good correlation from eq 1 that had an overall RMSD of 9.71 × 10−4 and a RAD % of 2.87 × 10−3 for benzoic acid and an overall RMSD of 3.28 × 10−4 and a RAD% of 5.05 × 10−3 for aspirin. The results coincide with published data for similar fitting equations in the literature13,19−21 that reported results of 1.15−5.30% for the RAD% and results varying from 0.33 to 4.01 × 10−4 for the RMSD leading to the conclusion that eq 1 gives an accurate correlation of the experimental solubility data in this study. The activity coefficient of the solubility data can be determined from the thermodynamic solubility relationship eqs 5 and 6.4,29 The following benzoic acid physical properties Δhm i = 18006 J/mol, Tm = 395.52 K, and Δcp = 57.86 J/mol·K were applied to calculate the activity coefficient which were obtained from the literature source.4 The following aspirin physical properties Δhm i = 29800 J/mol, Tm = 416.15 K, and Δcp = 90.81 J/mol·K were applied to calculate the activity coefficient were taken from the study12

Figure 2. Evolution of FBRM trends with changing temperature for the saturation point determination: ···, total counts ; - - -, coarse counts ; - · -, temperature in Kelvin. B

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Table 2. Experimental Solubility Temperature (T) Data for the Benzoic Acid Concentration Ratio (CR) in Various Solvents with Corresponding Mole Fraction (xi), Activity Coefficient (γi), and Relative Difference (RD) Measured at Atmospheric Pressure p = 0.1 MPaa CR (g/g)

T, K

0.4761 0.5622 0.6485 0.7461 0.8392 0.9794 1.1190 1.2118

278.00 285.50 292.23 298.99 304.78 312.56 319.32 323.49

0.2158 0.2450 0.3130 0.3520 0.3956 0.5024 0.5663 0.6389 0.7252

276.92 281.92 291.77 296.56 301.56 311.66 316.79 321.90 327.30

0.1500 0.1723 0.1974 0.2260 0.2586 0.2959 0.3388 0.3886 0.4459 0.4956

0.1140 0.1397 0.1607 0.1844 0.2113

xi methanol 0.1110 0.1285 0.1454 0.1637 0.1804 0.2044 0.2270 0.2412

RD, %

γi

CR (g/g)

T, K

0.04 0.06 0.02 −0.01 0.01 −0.04 0.02 −0.02

1.445 1.418 1.415 1.406 1.394 1.398 1.389 1.427

0.2734 0.3109 0.3524 0.3989 0.4509 0.5089 0.5748 0.6598 0.7352 0.8340

279.06 284.15 289.26 294.47 299.65 304.75 310.06 315.41 320.77 326.16

0.01 −0.02 0.03 0.14 −0.09 −0.04 −0.07 0.01 0.04

1.364 1.331 1.277 1.256 1.242 1.215 1.206 1.198 1.194

0.2562 0.2940 0.3364 0.3860 0.4405 0.5040 0.5775 0.6628 0.7630

278.65 284.29 289.86 295.54 301.27 307.10 313.04 319.06 325.20

276.45 281.66 287.16 292.73 298.25 303.76 309.36 315.05 320.74 325.16

1-butanol 0.1158 0.1295 0.1596 0.1760 0.1936 0.2337 0.2558 0.2794 0.3056 MIBK 0.1096 0.1238 0.1394 0.1564 0.1750 0.1953 0.2175 0.2417 0.2639 0.2810

0.29 0.51 0.18 −0.19 −0.28 −0.21 −0.16 −0.06 0.10 0.13

1.430 1.386 1.353 1.326 1.300 1.277 1.258 1.241 1.228 1.220

0.1631 0.1900 0.2124 0.2380 0.2773 0.3161 0.3601 0.4103 0.4677 0.5337 0.6103

279.67 285.24 289.24 293.36 298.93 303.76 308.76 313.66 318.65 323.56 326.50

276.27 283.74 288.69 293.67 298.34

isopropyl acetate 0.0855 0.1046 0.1185 0.1336 0.1502

1.52 0.06 −0.11 −0.30 0.27

1.827 1.700 1.634 1.577 1.517

0.2420 0.2760 0.3160 0.3620 0.4200

303.36 308.33 313.25 318.25 324.02

xi 1-propanol 0.1186 0.1327 0.1478 0.1641 0.1816 0.2003 0.2205 0.2423 0.2657 0.2910 MEK 0.1314 0.1479 0.1657 0.1856 0.2064 0.2293 0.2543 0.2813 0.3106 ethyl acetate 0.1053 0.1206 0.1329 0.1465 0.1667 0.1857 0.2062 0.2284 0.2523 0.2780 0.3057 isopropyl acetate 0.1682 0.1878 0.2091 0.2322 0.2599

RD%

γi

−0.01 0.09 0.10 −0.02 −0.07 0.07 −0.05 −0.1 −0.06 0.11

1.382 1.350 1.323 1.301 1.283 1.265 1.254 1.245 1.238 1.231

−0.03 −0.10 −0.06 0.17 0.02 0.01 −0.01 −0.01 −0.01

1.23912 1.2136 1.19164 1.17128 1.1592 1.14893 1.14171 1.13754 1.13617

4.14 −1.17 1.61 0.46 0.56 2.16 0.15 0.70 0.08 1.25 2.39

1.574 1.513 1.470 1.430 1.381 1.343 1.313 1.284 1.260 1.237 1.178

0.03 0.00 0.13 0.14 −0.20

1.473 1.432 1.393 1.361 1.332

a

Standard uncertainties u are u(CR) = 0.0001 g/g, u(xi) = 0.0001, u(T) = 0.4 K, u(P) = 0.005 MPa. The RD and activity coefficient (γi) are determined from eqs 3 and 5, respectively.

ln xi satγi sat = − +

ln xi satγi sat = − +

xsat i

Δhim ⎛ 1 1 ⎞ 1 ⎟− ⎜ − R ⎝T Tm ⎠ RT 1 R

∫T

T

m

Δc p T

∫T

evaluation, ΔCp is the difference in molar heat capacity between the melting and solid state of the solute, and R is the universal gas constant. The experimental solubility data is listed in Tables 2 and 3 with the corresponding results for RD from eq 3 and activity coefficient (γi) from eq 5. The experimental solubility from this work was compared to data in the literature for the solubility of benzoic acid in methanol, 1-propanol, and 1butanol8 while for aspirin the data was compared to MIBK,11 1-propanol, 1butanol, isobutanol, and ethyl acetate.16 The results of the comparison can be seen in Figures 3 and 4 for benzoic acid while the solubility of aspirin is compared in Figures 5 and 6. The results in Figures 3 and 4 show a good agreement between the experimental data from this work and the literature data8 for methanol, 1-propanol, and 1-butanol. There is a slight discrepancy in some of the data points for 1-butanol, and this

T

Δc pdT

m

dT

(5)

Δhim ⎛ 1 1 ⎞ 1 Δc p(T − Tm) ⎟− ⎜ − R ⎝T Tm ⎠ RT ⎛T ⎞ 1 Δc p ln⎜ ⎟ R ⎝ Tm ⎠

(6)

γsat i

where and represent the mole fraction and the activity coefficient of compound i in the saturated solution, Δhm i is the enthalpy of fusion for compound i, Tm is the melting point of the pure compound, T is the temperature at the point of C

DOI: 10.1021/acs.jced.5b00746 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Table 3. Experimental Solubility Temperature (T) Data for the Aspirin Concentration Ratio (CR) in Various Solvents with Corresponding Mole Fraction (xi), Activity Coefficient (γi), and Relative Difference (RD) Measured at Atmospheric Pressure p = 0.1 MPaa CR (g/g)

T, K

0.0380 0.0505 0.0632 0.0786 0.0970 0.1190 0.1452 0.1764 0.2134

275.86 283.66 289.86 296.16 302.67 308.68 315.16 321.37 327.91

0.0500 0.0696 0.0883 0.1100 0.1360 0.1668 0.2022 0.2438 0.2918 0.3472 0.4119

276.36 282.96 288.16 293.16 297.85 302.55 307.06 311.66 316.06 320.45 324.75

0.0240 0.0372 0.0481 0.0615 0.0776 0.0968 0.1195 0.1461 0.1772 0.2134 0.2330 0.2700

276.36 284.46 289.27 294.30 299.16 303.65 308.26 312.61 316.87 320.96 322.96 326.57

xi ethyl acetate 0.0154 0.0204 0.0254 0.0313 0.0384 0.0467 0.0564 0.0676 0.0807 1-propanol 0.0164 0.0227 0.0286 0.0354 0.0434 0.0527 0.0632 0.0752 0.0887 0.1038 0.1208 isobutanol 0.0098 0.0151 0.0194 0.0247 0.0309 0.0383 0.0469 0.0567 0.0679 0.0807 0.0875 0.1000

RD %

γi

CR (g/g)

T, K

0.61 −0.18 0.07 −0.02 −0.64 0.30 −0.13 0.29 −0.11

1.989 1.855 1.755 1.677 1.62 1.555 1.518 1.479 1.459

0.0170 0.0195 0.0248 0.0313 0.0392 0.0489 0.0606 0.0747 0.0918

277.86 281.16 287.78 293.97 300.25 307.15 313.56 320.16 327.15

0.34 1.43 0.85 0.15 0.55 0.58 0.73 0.22 0.13 −0.25 −0.46

2.242 1.933 1.761 1.622 1.494 1.389 1.299 1.226 1.161 1.106 1.057

0.0358 0.0453 0.0577 0.0729 0.0908 0.1119 0.1363 0.1648 0.1976 0.2354 0.2791

277.66 282.35 287.35 292.35 297.37 301.66 306.16 310.35 314.64 318.75 323.44

0.84 0.81 1.54 0.64 −0.01 0.59 0.02 0.11 0.08 0.36 0.30 −0.74

3.762 3.029 2.67 2.396 2.168 1.964 1.806 1.665 1.546 1.440 1.396 1.335

0.0360 0.0423 0.0524 0.0615 0.0776 0.0968 0.1135 0.1354 0.1772

277.46 281.76 287.96 292.96 300.18 307.27 312.47 318.36 327.95

xi isobutyl acetate 0.0109 0.0124 0.0157 0.0198 0.0247 0.0306 0.0376 0.046 0.0559 1-butanol 0.0145 0.0183 0.0232 0.0291 0.0360 0.0440 0.0531 0.0635 0.0752 0.0883 0.103 MIBK 0.0196 0.0230 0.0283 0.0331 0.0414 0.0511 0.0594 0.0700 0.0897

RD %

γi

0.41 0.83 −0.28 0.41 0.92 −0.37 0.20 0.32 −0.46

3.528 3.376 3.173 2.967 2.798 2.693 2.572 2.479 2.422

1.02 0.86 0.62 0.10 −1.08 0.39 0.22 0.93 0.75 0.87 −1.45

2.622 2.359 2.124 1.932 1.779 1.625 1.511 1.405 1.321 1.246 1.200

0.37 0.98 0.84 0.05 −0.13 −0.13 0.03 0.23 −0.25

1.928 1.849 1.769 1.727 1.665 1.616 1.585 1.557 1.539

a

Standard uncertainties u are u(CR) = 0.0001 g/g, u(xi) = 0.0001, u(T) = 0.3 K, u(P) = 0.005 MPa. The RD and activity coefficient (γi) are determined from eqs 3 and 5, respectively.

Table 4. Parameters A, B, and C from Equation 1 for the Benzoic Acid Solubility with the Corresponding RMSD and RAD Resultsa solvent methanol 1-propanol 1-butanol MEK MIBK ethyl acetate isopropyl acetate

A 3.32 4.07 4.15 3.98 4.27 4.90 5.08

B −1533.82 −1731.98 −1745.27 −1674.46 −1793.07 −2001.48 −2083.23

C −10.32 −11.61 −5.99 −11.24 −12.01 −13.44 −13.96

no. of pts 8 10 9 9 10 11 10

104 RMSD 0.50 1.27 1.27 0.12 1.69 3.78 5.04

Table 5. Parameters A, B, and C from Equation 1 for the Aspirin Solubility with the Corresponding RMSD and RAD % Resultsa

RAD % 0.03 0.05 0.05 1.25 0.07 0.21 0.28

a

No. of pts (number of experimental data points). The values for RMSD and RAD are determined from eqs 2 and 4, respectively.

C

no. of pts

104 RMSD

RAD %

solvent

A

B

ethyl acetate isobutyl acetate 1-propanol 1-butanol isobutanol MIBK

6.40

−2870.33

−35.11

11

5.84

0.75

6.41

−3038.03

−20.22

9

2.50

0.40

9.34 9.77 10.59 5.97

−3717.28 −3890.47 −4207.76 −2747.27

−19.68 −50.41 −35.20 −2747.27

9 12 11 9

1.41 2.75 2.94 1.48

0.47 0.50 0.52 0.33

a

No. of pts (number of experimental data points). The values for RMSD and RAD are determined from eqs 2 and 4, respectively.

may be due to differences in experimental procedure and apparatus that were all determined gravimetrically in the literature.8 The results in Figures 5 and 6 show a good agreement between the experimental data from this work and

the literature data11for 1-propanol, 1-butanol, isobutanol, ethyl acetate, and MIBK. The results for 1-propanol, 1-butanol, and isobutanol show some slight discrepancies that may be due to D

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Figure 5. Solubility of aspirin in 1-propanol, isobutanol, and ethyl acetate on a mole fraction basis with respect to temperature compared to literature data: □, 1-propanol this work; Δ, isobutanol this work; x, ethyl acetate; ○, 1-propanol from Acree et al.;16 +, isobutanol from Acree et al.;16 ◊, ethyl acetate from Acree et al.16

Figure 3. Solubility of benzoic acid in methanol and 1-butanol on a mole fraction basis with respect to temperature compared to literature data: □, methanol this work; ○, 1-butanol this work; Δ, methanol from Acree et al;8 +, 1-butanol from Acree et.8

Figure 6. Solubility of aspirin in 1-butanol and MIBK on a mole fraction basis with respect to temperature: ◊, 1-butanol this work; +, MIBK this work; Δ, 1-butanol from literature Acree et al;16 ○, MIBK from literature source Hahnenkamp et al.11

Figure 4. Solubility of benzoic acid in 1-propanol on a mole fraction basis with respect to temperature compared to literature data: ◊, 1propanol this work; x, 1-propanol from Acree et al.8

differences in experimental procedure and apparatus with all the literature solubility data collected by spectrophotometric measurements.16 Although the data was collected and reported in terms of a concentration ratio CR (g of solute/g of solvent), it was converted to mole fraction for the purpose of fitting the data by applying eq 1. The data was interpolated for each solvent with a temperature interval of 2 K over a range of 278.15−323.15 K with the results displayed on a mole fraction basis in Figure 7 and on a mass basis displayed in Figure 8 for benzoic acid and the results for aspirin are displayed on a mole fraction basis in Figure 9 and on a mass basis in Figure 10. The visual finding from Figures 7−10 highlights a good correlation between the experimental data and the extrapolated data from eq 1 thus confirming the outcomes from eqs 2 and 4, which are listed in Tables 4 and 5 for benzoic acid and aspirin, respectively. Applying the correlation expression to the data on mole fractions gives a more accurate representation of the experimental data then if it was applied on a mass fraction, although reviewing the data on a mass basis leads to a better

Figure 7. Experimental and correlated solubility data of benzoic acid on a mole fraction basis with respect to temperature in the solvents: □, methanol; ◊, 1-propanol; ○, 1-butanol; Δ, MEK; x, MIBK; −, ethyl acetate; +, isopropyl acetate. The solid/dashed lines are the correlated results from eq 1 for each solvent. E

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understanding of the change in solubility with respect to both temperature and solvent. Looking at the experimental solubility data on a mole fraction basis for both systems in Figures 7 and 9 it is evident that the data is very clustered making it quite difficult to interpret the data and make exact conclusions to which solvent or solvents offer the most optimal solubility characteristics. Therefore, plotting the solubility data on mass ratio as in Figures 8 and 10 for both systems gives a better understanding of the affect of temperature on the solubility in each solvent. The plot of activity coefficient with respect to temperature is displayed in Figure 11 and Figure 12, where the activity

Figure 8. Experimental and correlated solubility data of benzoic acid on a mass basis with respect to temperature in the solvents: □, methanol; ◊, 1-propanol; ○, 1-butanol; Δ, MEK; x, MIBK; −, ethyl acetate; +, isopropyl acetate. The solid/dashed lines are the correlated results from eq 1 for each solvent.

Figure 11. Plot of activity coefficient of benzoic acid with respect to temperature in the solvents: □, methanol; ◊, 1-propanol; ○, 1butanol; Δ, MEK; x, MIBK; −, ethyl acetate; +, isopropyl acetate. The solid/dashed lines are the correlated results from eq 1 for each solvent.

Figure 9. Experimental and correlated solubility data of aspirin on a mole fraction basis with respect to temperature in the solvents: □, 1propanol; ◊, 1-butanol; ○, isobutanol; Δ, ethyl acetate; x, isobutyl acetate; −, MIBK. The solid/dashed lines are the correlated results from eq 1 for each solvent.

Figure 12. Plot of activity coefficient of aspirin with respect to temperature in the solvents: □, 1-propanol; ◊, 1-butanol; ○, isobutanol; Δ, ethyl acetate; x, isobutyl acetate; −, MIBK. The solid/dashed lines are the correlated results from eq 1 for each solvent.

coefficient of the experimental data (symbols) can be observed to be in good agreement with the fitted results (solid/dashed lines) from eq 1. The activity coefficient follows a decreasing trend with increase in temperature for all of the data except for benzoic acid in methanol which coincides with the literature.30 The activity coefficient can be utilized to gauge the ideal behavior of the experimental solubility data, as a solution mixture is said to be ideal when γi = 1.31 The results in Table 2

Figure 10. Experimental and correlated solubility data of aspirin on a mass fraction basis with respect to temperature in the solvents: □, 1propanol; ◊, 1-butanol; ○, isobutanol; Δ, ethyl acetate; x, isobutyl acetate; −, MIBK. The solid/dashed lines are the correlated results from eq 1 for each solvent.

F

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and Table 3 show that the activity coefficient for both systems become closer to ideality with increasing temperature.

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CONCLUSION The solubility of benzoic acid has been measured in seven pure solvents over a temperature range of 275.39−327.03 K while the solubility of aspirin was measured in six pure solvents over a temperature range of 275.12−327.91 K. A good agreement between experimental data and the literature data was observed for the solubility of benzoic and aspirin in multiple solvents. A modified van’t Hoff equation was applied to both systems to correlate the data on a mole fraction basis over a temperature range of 278.15−323.15 K. The fit of the solubility data by the modified van’t Hoff equation shows a good correlation with the experimentally determined values, which was shown to have a RMSD as low as 0.12 × 10−4 and as high as 5.04 × 10−4 for benzoic acid while results were reported for aspirin as low as 1.41 × 10−4 and as high as 5.84 × 10−4. The RAD% for the individual solvents were shown to be as low as 0.03% and as high as 1.25% for benzoic acid while results were reported for aspirin as low as 0.40% and as high as 0.75%. which coincide with a similar apelblat method published in the literature20,26,27

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Telephone: +353-1-715-1954. Fax: +353-1-716-1177. Notes

The authors declare no competing financial interest.

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REFERENCES

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DOI: 10.1021/acs.jced.5b00746 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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(31) Sandler, S. I. Mixture Phase Equilibria Involving Solids. In Chemical, Biochemical and Engineering Thermodynamics, 4th ed.; John Wiley & Sons: New York, 2006; Chapter 12, pp 658−662.

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DOI: 10.1021/acs.jced.5b00746 J. Chem. Eng. Data XXXX, XXX, XXX−XXX