Determination and Correlation of Solubility of Borneol, Camphor, and

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Determination and Correlation of Solubility of Borneol, Camphor, and Isoborneol in Different Solvents Jingjing Chen,†,‡ Jingjing He,‡ Ningxin Li,‡ Huidong Zheng,*,‡ and Suying Zhao‡ †

College of Materials Science and Engineering and ‡College of Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108, P. R. China

J. Chem. Eng. Data Downloaded from pubs.acs.org by UNIV OF LOUISIANA AT LAFAYETTE on 03/29/19. For personal use only.

S Supporting Information *

ABSTRACT: The solubility of borneol, camphor, and isoborneol in four solvents (i.e., acetone, ethanol, p-cymene, and pxylene) was measured by the static equilibrium method within the temperature range of 296.65−348.85 K under the atmosphere. The fusion points and fusion enthalpies of borneol and isoborneol were determined by differential scanning calorimetry. The Apelblat equation, Wilson model, and NRTL model were employed to correlate the measured solubility data, and the NRTL model fits the measured data better. Mixing properties of each solute−solvent pair are calculated by the NRTL model.

1. INTRODUCTION Camphor is a bicyclic monoterpene and is one of the oldest known organic compounds. It has been widely used in fragrance and pharmaceutical industries1 as the functional component in mothproof products and in analgesics and rubefacients for the treatment of minor muscle aches and pains.2 Camphor exhibits two asymmetric carbon atoms, and there are two enantiomers: D-camphor and L-camphor. Pure Dcamphor (CAS no. 464-49-3) and L-camphor (CAS no. 46448-2) are produced naturally by the camphor tree and other plants, and synthesized camphor is racemic DL-camphor (CAS no. 76-22-2). Industrial synthesis of camphor usually starts with turpentine as the raw material.3 Dehydrogenation of isoborneol is the last and key reaction to obtain camphor with borneol as the main byproduct.4−6 Compared with vacuum distillation, crystallization/recrystallization is an easier and more energy-efficient method for the separation and purification of the camphor product from borneol and isoborneol. However, there are few literature studies about the solubility data of these components in any solvent, which is necessary for the design of the crystallization process. Furthermore, the latest thermodynamic properties, such as the fusion point and enthalpy of D-, L-, DLcamphor, and L-borneol have been recently reported,7−9 while those of DL-borneol and DL-isoborneol have seldom been found. In this paper, the solubility of borneol, camphor, and isoborneol in four solvents (acetone, ethanol, p-cymene, and pxylene) from 296.65 to 348.85 K was measured, and the fusion © XXXX American Chemical Society

points and enthalpies of DL-borneol and DL-isoborneol were determined. The solubility data were correlated with the modified Apelblat equation, Wilson model, and the NRTL model. The van’t Hoff equation was used to calculate the dissolution enthalpy and entropy.

2. EXPERIMENTAL SECTION 2.1. Materials. The source, purity, and purification method of the involved materials are listed in Table 1. The borneol, camphor, and isoborneol used in this work are all racemic mixtures, and their structures are given in Figure 1. The purity of all the materials is determined by a gas chromatograph (see Section 2.4). 2.2. Differential Scanning Calorimetry. The fusion point Tfus and fusion enthalpy ΔHfus of borneol and isoborneol were measured by differential scanning calorimetry (DSC) (DSC 214, NETZSCH) using the continuous method with a heating rate of 2 K/min. The DSC was periodically calibrated using water, gallium, naphthalene, indium, and tin. Approximately, 5.0 mg of borneol or isoborneol was required in the measurement. The deviation of the weight measurements is about 0.01 mg, which can be acceptable in this work. 2.3. X-ray Diffraction. The X-ray diffraction (XRD) was performed to determine the crystal structure of the borneol, camphor, and isoborneol in the raw materials and the bottom Received: January 15, 2019 Accepted: March 15, 2019

A

DOI: 10.1021/acs.jced.9b00045 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Materials material

CAS no.

source

puritya (mass %)

purification method

borneol camphor isoborneol acetone ethanol p-cymene p-xylene 2-ethyl-1-hexanol

507-70-0 76-22-2 124-76-5 67-64-1 64-17-5 99-87-6 106-42-3 104-76-7

Fujian Green Pine Co., Ltd. Fujian Green Pine Co., Ltd. Fujian Green Pine Co., Ltd. Sinopharm Chemical Reagent Beijing Co., Ltd. Sinopharm Chemical Reagent Beijing Co., Ltd. Fujian Green Pine Co., Ltd. Aladdin Industrial Corporation Sinopharm Chemical Reagent Beijing Co., Ltd.

≥99.0 ≥99.0 ≥99.0 ≥99.5 ≥99.7 ≥99.0 ≥99.0 ≥99.7

recrystallization recrystallization recrystallization none none vacuum distillation none none

a

Determined by a gas chromatograph (see Section 2.4).

Figure 1. Structures of borneol, camphor, and isoborneol.

(FID) and a capillary column (OV-101 30 m × 0.25 mm × ̀ 0.25 im). The column temperature was programmed as 333 K hold 1 min; heat at 10 K/min for 10 min; and 433 K hold 2 min. Nitrogen was used as the carrier gas. 2-Ethyl-1-hexanol was selected as the internal standard substance of the three solutes. The same analysis process was applied to determine the purity of the materials. The mole fraction solubility x of the solutes in different solvents was calculated as following

phases of each system. The XRD patterns were recorded by DY5261/Xpert3 (CEM, USA) equipped with a Cu Kα radiation at 30 kV and 15 mA in the 2θ range between 10° and 40°. 2.4. Solubility Measurement. The solubility of borneol, camphor, and isoborneol was determined by the gravimetric method.10 The apparatus consisted of a 10 mL dual-wall flask and a temperature control system (Figure 2). Before the

x=

ω/M ω/M + ωs /Ms

(1)

where ω and ωs represent the mass fraction of the solute and the solvent, respectively; M and Ms are the molar mass of the solute and the solvent, respectively.

3. THERMODYNAMIC MODELS Figure 2. Experimental apparatus: (1) thermostatic water bath; (2) mercurial thermometer; (3) dual-wall flask; (4) stirring bar; and (5) magnetic stirrer.

3.1. Modified Apelblat Equation. The modified Apelblat equation11,12 (eq 2) is a semiexperimental expression deduced from the Clausius−Clapeyron equation. It is widely used in the correlation of solid−liquid equilibrium data to show the relationship between the mole fraction of the solute and the temperature

experiment, an excess amount of the solute (i.e., borneol, camphor, or isoborneol) and the corresponding solvent was added into the flask. The mixture was constantly stirred at the set temperature for 4 h to reach the equilibrium and then settled for at least 4 h to ensure the complete precipitation of the undissolved solid. The equilibrium system was heated by the circulating water through the jacket from a thermostatic water bath. The system temperature was measured by a mercurial thermometer with an uncertainty of ±0.05 K. When the system was equilibrated, the supernatant was taken by a pre-heated pipette gun, diluted by the corresponding solvent, and analyzed by gas chromatography. The bottom solid phase was collected for XRD analysis. Each measurement was conducted for at least twice, and the mean values were taken as the final experiment data. The concentration of borneol, camphor, or isoborneol in the samples was determined by a gas chromatograph (GC2014, SHIMADZU) equipped with a flame ionization detector

ln x = A + B /T + C ln T

(2)

where T is the absolute temperature; A, B, and C are the regressed empirical parameters. The values of A and B reflect the variation in the solution activity coefficient and indicate the nonideality of the solute in the solution. The value of C represents the effect of temperature on the fusion enthalpy as a deviation of heat capacity.13 3.2. Wilson Model. Wilson model is widely used to describe the solubility behavior of a solute in solvents. Based on the traditional thermodynamic theory, a universal equation14 for describing solid−liquid equilibrium may be expressed as follows B


Journal of Chemical & Engineering Data ln(x1γ1) =

Article

ΔHtp ijj 1 Ttp y 1 yzzz ΔCp ijj Ttp jj − − + 1zzzz jjln zz − j R j Ttp Tz R k T T { k { ΔV (p − ptp ) − (3) RT

At a certain pressure, eq 3 can be simplified as15 ln x1 =

ΔHfus ijj 1 1 zy − zzz − ln γ1 jj j R k Tfus T z{

(4)

where x1 is the mole fraction of the solute, and γ1 is the activity coefficient of the solute. For the binary system, the activity coefficient γ1 can be expressed by the Wilson model as ij yz Λ12 Λ 21 zz ln γ1 = −ln(x1 + Λ12x 2) + x 2jjj − zz jx + Λ x + Λ x x 1 12 2 2 21 1 k {

Figure 3. XRD patterns of borneol in the material and the bottom phases.

(5)

ln Λ12 = ln

V2 b + a12 + 12 V1 T

(6)

ln Λ 21 = ln

V1 b + a 21 + 21 V2 T

(7)

where V1 and V2 are the mole volumes of the solute and the solvent, respectively; a12, a21, b12, and b21 are the Wilson model parameters. 3.3. NRTL Model. The activity coefficient γ1 in eq 4 can also be calculated by the NRTL model ln γi =

∑j τjiGjixj ∑k Gkixk

τij = cij +

dij T

,

Gij = exp( −αijτij),

+

∑ j

ij y jjτ − ∑l τljGljxj zzz jj ij z ∑k Gkjxk zz ∑k Gkjxk j k { Gijxj

(8)

τii = τjj = 0

(9)

Gii = Gjj = 1

Figure 4. XRD patterns of camphor in the material and the bottom phases.

(10)

where cij and dij are the NRTL model parameters; αij is a criterion of the nonrandomness of the solution, which is chosen to be 0.2 in this work.

4. RESULTS AND DISCUSSION 4.1. Property of the Solutes. 4.1.1. Differential Scanning Calorimetry. The measured fusion points (Tfus) and fusion enthalpies (ΔHfus) of borneol and isoborneol are listed in Table 2. The fusion points were characterized as the temperatures of the phase transition peaks; the fusion enthalpies were determined by integration of the phase transition peaks using a linear baseline. 4.1.2. XRD Analysis. The XRD patterns of borneol, camphor, and isoborneol materials and the bottom solid phases were measured (Figures 3−5). There is no distinct Table 2. Fusion Points and Fusion Enthalpies of Borneol and Isoborneola compound

Tfus (K)

ΔHfus (kJ/mol)

borneol isoborneol

478.3 ± 0.5 482.7 ± 0.5

8.29 ± 0.05 8.80 ± 0.08

Figure 5. XRD patterns of isoborneol in the material and the bottom phases.

difference between the patterns of the materials and the bottom solid phases except the small difference in the intensity of peaks, which may result from the different preferential growth orientation of isoborneol and camphor in different

The experimental pressure is 101.3 ± 0.5 kPa.

a

C



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solvents. The XRD results indicate that the crystal forms of the three solutes in the dynamic liquid−solid equilibrium are the same as the pure materials and no crystallosolvate is formed in the equilibrium system. 4.2. Solubility of Borneol, Camphor, and Isoborneol. The average experimental data of the solubility of borneol, camphor, and isoborneol in acetone, ethanol, p-cymene, and pxylene at the temperature range of (296.65−348.85) K are listed in Tables 3−5, respectively.

Table 4. Mole Fraction Solubility (x) of Camphor in Different Solvents at Each Temperaturea solvent

T (K)

x

xApel

xWilson

xNRTL

acetone

303.15 308.15 313.55 319.25 323.15 303.15 308.15 313.15 318.15 322.95 327.95 333.35 338.15 343.15 303.85 308.05 313.15 317.95 323.65 328.15 333.35 337.95 343.05 303.05 308.15 313.15 318.15 323.25 327.85 328.15 333.15 338.35 343.15

0.5529 0.5707 0.5940 0.6138 0.6266 0.3655 0.3958 0.4123 0.4509 0.5084 0.5376 0.5876 0.6304 0.6992 0.5802 0.5894 0.6007 0.6088 0.6241 0.6308 0.6410 0.6518 0.6642 0.6003 0.6369 0.6600 0.6833 0.7139 0.7359 0.7387 0.7702 0.7948 0.8240

0.5523 0.5723 0.5929 0.6135 0.6270 0.3642 0.3917 0.4224 0.4567 0.4934 0.5358 0.5871 0.6379 0.6967 0.5806 0.5893 0.5999 0.6099 0.6219 0.6314 0.6425 0.6523 0.6632 0.6037 0.6314 0.6586 0.6858 0.7136 0.7385 0.7402 0.7672 0.7953 0.8211

0.5528 0.5709 0.5935 0.6143 0.6264 0.3554 0.3915 0.4281 0.4653 0.5015 0.5409 0.5872 0.6348 0.6923 0.5813 0.5896 0.5998 0.6096 0.6214 0.6309 0.6421 0.6523 0.6637 0.6030 0.6319 0.6593 0.6860 0.7130 0.7377 0.7393 0.7669 0.7960 0.8215

0.5525 0.5721 0.5927 0.6134 0.6272 0.3676 0.3931 0.4233 0.4584 0.4965 0.5397 0.5878 0.6290 0.6684 0.5805 0.5894 0.6000 0.6099 0.6217 0.6311 0.6422 0.6522 0.6636 0.6025 0.6323 0.6597 0.6863 0.7131 0.7375 0.7391 0.7663 0.7954 0.8224

ethanol

Table 3. Mole Fraction Solubility (x) of Borneol in Different Solvents at Each Temperaturea solvent

T (K)

x

xApel

xWilson

xNRTL

acetone

297.05 303.15 309.55 313.75 318.75 322.75 327.15 297.95 302.25 307.35 313.15 318.05 323.55 327.25 333.05 336.35 338.75 343.55 348.70 296.65 305.35 309.15 314.35 319.55 323.15 328.75 332.95 338.95 343.75 348.85 298.15 300.45 304.35 307.75 313.25 317.85 320.95 324.15 327.65 332.55 334.15 337.35 341.55 344.85 348.85

0.0672 0.0905 0.1196 0.1568 0.2167 0.2696 0.3574 0.1121 0.1135 0.1161 0.1197 0.1246 0.1330 0.1369 0.1447 0.1513 0.1591 0.1703 0.1858 0.1547 0.1822 0.1982 0.2225 0.2507 0.2652 0.2947 0.3226 0.3671 0.3940 0.4330 0.1453 0.1515 0.1596 0.1719 0.1886 0.2085 0.2245 0.2404 0.2582 0.2931 0.3080 0.3407 0.3752 0.4091 0.4640

0.0672 0.0890 0.1237 0.1563 0.2104 0.2703 0.3605 0.1124 0.1135 0.1158 0.1199 0.1246 0.1312 0.1366 0.1465 0.1531 0.1584 0.1701 0.1848 0.1532 0.1845 0.1997 0.2224 0.2472 0.2657 0.2968 0.3221 0.3615 0.3959 0.4354 0.1457 0.1508 0.1606 0.1705 0.1894 0.2084 0.2231 0.2401 0.2611 0.2952 0.3076 0.3348 0.3756 0.4122 0.4629

0.0665 0.0897 0.1245 0.1567 0.2112 0.2724 0.3573 0.1122 0.1135 0.1160 0.1201 0.1246 0.1311 0.1364 0.1463 0.1529 0.1582 0.1703 0.1855 0.1543 0.1841 0.1991 0.2215 0.2466 0.2656 0.2978 0.3239 0.3637 0.3968 0.4326 0.1416 0.1486 0.1611 0.1727 0.1931 0.2121 0.2261 0.2421 0.2615 0.2935 0.3055 0.3324 0.3742 0.4125 0.4640

0.0674 0.0891 0.1234 0.1562 0.2117 0.2728 0.3573 0.1120 0.1135 0.1162 0.1204 0.1249 0.1312 0.1363 0.1459 0.1524 0.1577 0.1701 0.1866 0.1549 0.1838 0.1986 0.2210 0.2463 0.2655 0.2979 0.3242 0.3639 0.3970 0.4325 0.1438 0.1503 0.1617 0.1724 0.1915 0.2099 0.2240 0.2401 0.2602 0.2934 0.3058 0.3332 0.3751 0.4129 0.4640

ethanol

p-cymene

p-xylene

p-cymene

p-xylene

The experimental pressure is 101.3 ± 0.5 kPa; the standard uncertainty of the temperature is u(T) = 0.05 K; and the relative uncertainty of x is u(x) = 0.005. a

Generally, the solubility of camphor in the tested solvents is the highest within the temperature range, while that of borneol is the lowest. As shown in Figures 6−8, the solubility of borneol, camphor, and isoborneol increases with the rising temperature in all tested solvents (acetone, ethanol, p-cymene, and p-xylene). The increasing rates of the solubility of borneol and isoborneol in acetone and camphor in ethanol (alcohol− ketone pairs) are higher than the other pairs, while for the alcohol−alcohol pairs or ketone−ketone pairs, the variation of solubility is relatively small. This may attribute to the stronger interaction between alcohol and ketone molecules. These results could confirm the feasibility of crystallization as the purification process of camphor and help with the selection of the solvent in the process. 4.3. Correlation of Solubility Data. As mentioned in Section 3, three models (i.e., modified Apelblat equation, Wilson model, and NRTL model) are applied in the correlation of the experimental solubility data in this work. The fusion point and fusion enthalpy of camphor are 448.0 K and 5.9 kJ/mol, respectively,7 and those of borneol and isoborneol are listed in Table 2.

The experimental pressure is 101.3 ± 0.5 kPa; the standard uncertainty of the temperature is u(T) = 0.05 K; and the relative uncertainty of x is u(x) = 0.005.

a

D



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Table 5. Mole Fraction Solubility (x) of Isoborneol in Different Solvents at Each Temperaturea solvent

T (K)

X

xApel

xWilson

xNRTL

acetone

296.95 298.85 303.35 305.65 307.65 312.45 317.25 321.25 298.35 303.15 307.65 310.75 313.05 316.35 318.35 320.15 323.95 327.75 328.05 333.05 338.30 343.15 348.05 303.55 308.25 313.15 318.45 322.85 328.45 334.25 337.05 342.75 303.55 308.25 313.15 318.45 323.55 329.05 335.35 339.50 345.05

0.3369 0.3428 0.3684 0.3798 0.3975 0.4242 0.4532 0.4773 0.3631 0.3687 0.3844 0.3859 0.3943 0.4001 0.4062 0.4194 0.4231 0.4420 0.4427 0.4561 0.4876 0.4988 0.5138 0.3170 0.3281 0.3407 0.3581 0.3773 0.3970 0.4154 0.4202 0.4402 0.3094 0.3288 0.3446 0.3575 0.3800 0.4141 0.4401 0.4616 0.4968

0.3346 0.3448 0.3696 0.3827 0.3943 0.4229 0.4527 0.4784 0.3606 0.3707 0.3811 0.3888 0.3948 0.4038 0.4096 0.4149 0.4267 0.4393 0.4403 0.4581 0.4782 0.4983 0.5200 0.3146 0.3289 0.3441 0.3608 0.3750 0.3933 0.4128 0.4223 0.4419 0.3112 0.3257 0.3423 0.3621 0.3832 0.4082 0.4401 0.4631 0.4967

0.3358 0.3443 0.3680 0.3817 0.3942 0.4249 0.4544 0.4766 0.3627 0.3707 0.3799 0.3873 0.3932 0.4025 0.4086 0.4142 0.4268 0.4402 0.4413 0.4598 0.4797 0.4982 0.5168 0.3133 0.3282 0.3438 0.3610 0.3755 0.3940 0.4132 0.4223 0.4399 0.3116 0.3253 0.3414 0.3609 0.3821 0.4078 0.4406 0.4638 0.4957

0.3358 0.3442 0.3680 0.3817 0.3942 0.4245 0.4541 0.4770 0.3640 0.3703 0.3789 0.3863 0.3924 0.4021 0.4085 0.4144 0.4276 0.4412 0.4424 0.4607 0.4800 0.4977 0.5153 0.3173 0.3273 0.3410 0.3592 0.3763 0.3958 0.4144 0.4222 0.4395 0.3110 0.3260 0.3421 0.3613 0.3822 0.4075 0.4399 0.4633 0.4965

ethanol

p-cymene

p-xylene

Figure 6. Experimental mole fraction solubility of borneol in different solvents.

Figure 7. Experimental mole fraction solubility of camphor in different solvents.

The experimental pressure is 101.3 ± 0.5 kPa; the standard uncertainty of the temperature is u(T) = 0.05 K; and the relative uncertainty of x is u(x) = 0.005.

a

The calculated values for each solute−solvent system are listed in Tables 3−5. The xApel, xWilson, and xNRTL refer to the calculated mole fraction solubility by modified Apelblat equation, Wilson model, and NRTL model, respectively. The relative deviation (RD) of the calculated values is listed in Table S1 of the Supporting Information. The root-meansquare deviation (rmsd) and the average RD (ARD) of the calculated data for each solute−solvent system are calculated to evaluate the deviations between the predicted and measured solubility

Figure 8. Experimental mole fraction solubility of isoborneol in different solvents. N

ARD =

N

rmsd =

1 ∑ (xiexp − xical)2 N i=1

x cal − x exp 1 ∑ i exp i × 100 N i=1 xi

(12)

where i is the number of the experimental point; N is the total number of experimental points; and the superscripts cal and

(11) E



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Table 6. Correlation Results of the Apelblat Equation solutes borneol

camphor

isoborneol

solvents

A

B

C

rmsd

ARD

acetone ethanol p-cymene p-xylene acetone ethanol p-cymene p-xylene acetone ethanol p-cymene p-xylene

−738.85 −252.93 −39.988 −300.30 40.649 −128.23 −8.5779 11.700 0.3455 −77.109 −5.8953 −103.72

29 443 11 057 67.614 12 189 −2439.3 4627.9 84.168 −1252.6 −1253.1 2971.6 −534.86 3896.5

111.88 37.500 6.6550 45.194 −5.8094 19.592 1.3569 −1.4125 0.4882 11.605 1.1374 15.696 maximum average

0.0031 0.0010 0.0025 0.0021 0.0009 0.0070 0.0011 0.0026 0.0020 0.0039 0.0025 0.0031 0.0070 0.0027

1.36 0.50 0.73 0.54 0.13 1.12 0.14 0.31 0.48 0.76 0.64 0.68 1.36 0.62

Table 7. Correlation Results of the Wilson Model solutes borneol

camphor

isoborneol

solvents

a12

b12

a21

b21

rmsd

ARD


10.119 −1.6364 0.8696 3.3649 −13.038 7.3058 −0.0711 5.3772 −4.1268 −3.3867 −72.782 −0.7049

−2973.2 −110.42 −219.85 −869.21 4456.6 −1706.9 413.10 −1041.4 1770.5 1688.2 21 400 638.95

28.766 −3.7279 6.8985 26.439 30.769 47.643 −2.9841 35.516 18.229 8.6222 0.9829 11.814

−9822.4 924.36 −2575.7 −9616.9 −9750.1 −17 334 483.94 −12 878 −5941.5 −3274.1 46.978 −4404.2 maximum average

0.0030 0.0009 0.0022 0.0033 0.0004 0.0088 0.0011 0.0024 0.0016 0.0034 0.0022 0.0031 0.0088 0.0027

1.38 0.43 0.66 1.15 0.05 1.62 0.14 0.28 0.35 0.64 0.51 0.72 1.62 0.66

Table 8. Correlation Results of the NRTL Model solutes borneol

camphor

isoborneol

solvents

c12

d12

c21

d21

rmsd

ARD


−34.603 2.7114 −8.1855 −30.488 −10.171 −18.183 5.0205 −37.942 −30.381 2.5861 7.4444 −9.0074

12 108 −1264.1 3286.8 12 009 3247.0 7106.8 −1971.4 16 448 9351.1 −1537.5 −2868.1 2310.0

−13.059 −0.9873 −0.0735 −10.499 4.0314 −3.0838 55.823 −24.594 16.331 27.215 37.090 −44.035

3777.6 1488.3 −271.52 2881.3 −1550.6 333.35 −13 014 6602.5 −5264.0 −6867.8 −9314.8 16 223 maximum average

0.0027 0.0010 0.0023 0.0026 0.0010 0.0119 0.0010 0.0023 0.0015 0.0034 0.0018 0.0030 0.0119 0.0029

1.27 0.58 0.64 0.74 0.14 1.44 0.12 0.26 0.31 0.62 0.35 0.64 1.44 0.59

exp represent the calculated and experimental data, respectively. The deviations for each model and each solute−solvent system are listed in Tables 6−8, as well as the obtained parameters of each model. As shown in the tables, the averages of rmsd and ARD for all the measured solute−solvent pairs are 0.0027 and 0.62, respectively, indicating good coincidence between the experimental data and the predicted values of the models. The maximums of rmsd and ARD of all the involved models are observed in the camphor−ethanol system, which could be

attributed to the relatively higher experimental errors. Generally, all the models can well describe the dissolution behavior of the measured systems, and the prediction of the NRTL model is relatively more accurate than the Apelblat equation and Wilson model. 4.4. Mixing Properties of Solution. The mixing properties of the solution could provide detailed information on understanding the dissolution behavior, and they can be calculated according to the Lewis−Randall rule. F



■

For the ideal solution, the mixing Gibbs energy and the mixing enthalpy in pure solvent can be calculated as16 id

Δmix G = RT (x1 ln x1 + x 2 ln x 2)

*E-mail: [email protected]. ORCID

Δmix H = 0

Jingjing Chen: 0000-0002-8514-4999 Huidong Zheng: 0000-0002-8346-7284

(14)

where x1 and x2 are the mole fractions of the solute and the corresponding solvent. For the nonideal solution, the mixing property can be obtained as the sum of the mixing property in the ideal solution and the excess property (GE and HE) in real solution

Funding

This work was supported by the National Natural Science Foundation of China (no. 21376053), the Major Project on the Integration of Industry Education and Research of Fujian Province (no. 2014H6002), the Regional Development Project of Fujian Province (no. 2016H4023), and the Program for New Century Excellent Talents in Fujian Province University (no. HG2017-17).

Δmix G = Δmix Gid + GE + GE = RT (x1 ln γ1 + x 2 ln γ2) ÅÄÅ Δmix H = Δmix H + H + H = −T ÅÅ ÅÅÇ E

E

ÑÉ /T ) ÑÑÑ ÑÑ ∂T ÑÑÑÖ

2Å ÅÅ ∂(G

(15)

Notes

E

The authors declare no competing financial interest.

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With the obtained NRTL parameters, the mixing Gibbs energy ΔmixG and the mixing enthalpy ΔmixH for the measured systems are calculated and listed in Table S2 of the Supporting Information. As listed in the table, the ΔmixG values for all the systems are negative; therefore, the dissolution of the solutes in the selected solvents is favorable and spontaneous. The ΔmixH values are negative in most cases, indicating an exothermic dissolution of the solutes, while the dissolution of borneol in ethanol, camphor in p-cymene, and isoborneol in ethanol and p-cymene is endothermic. This reflects the different intermolecular interactions between the solute and the solvent. The enthalpy is endothermic when the interaction between solute and solvent molecules is stronger than that between the solute molecules, while a weaker interaction between solute and solvent molecules results in the exothermic enthalpy.17

REFERENCES

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5. CONCLUSIONS In this work, the solubility of borneol, camphor, and isoborneol in four different solvents (acetone, ethanol, p-cymene, and pxylene) has been experimentally determined at the temperature ranging from 296.65 to 348.85 K under the atmosphere. The solubility of borneol, camphor, and isoborneol in all the examined solvents increases with the rising temperature. The Apelblat equation, Wilson model, and NRTL model are applied to correlate the measured solubility data, and the NRTL model provides better prediction for the binary systems than the others. The mixing Gibbs energy ΔmixG and the mixing enthalpy ΔmixH for the measured systems are calculated by the NRTL model. The negative ΔmixG values indicate a spontaneous dissolution of borneol, camphor, and isoborneol in the selected solvents. The dissolution is exothermic in most cases, while it is an endothermic process for camphor and isoborneol in p-cymene.

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.9b00045. RD values of the predicted solubility by three models and the values of ΔmixG and ΔmixH for the measured binary pairs (PDF) G



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(16) Smith, J. M.; Ness, H. C. V.; Abbott, M. M. Introduction to Chemical Engineering Thermodynamics; McGraw-Hill: New York, US, 2001. (17) Zhang, K.; Shen, H.; Xu, S.; Zhang, H.; Zhu, M.; Shi, P.; Fu, X.; Yang, Y.; Gong, J. Thermodynamic Study of Solubility for Pyrazinamide in Ten Solvents from T = (283.15 to 323.15) K. J. Chem. Thermodyn. 2017, 112, 204−212.

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Determination and Correlation of Solubility of Borneol, Camphor, and

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