Measurement and Correlation of the Solubilities of Azoxystrobin

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

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Measurement and Correlation of the Solubilities of Azoxystrobin, Flutriafol, and Tebuconazole in Subcritical 1,1,1,2-Tetrafluoroethane Yufang Zhao,†,§ Qingyuan Zhao,†,‡,§ Xiaomei Feng,*,† Yuqian Han,*,† and Changhu Xue† †

College of Food Science and Engineering, Ocean University of China, Daxue Road 5, Qingdao, Shandong 266003, China Qingdao Yuance Biological Technology Co., Ltd., Qingdao International Academician Park, The Golden Waterway 171, Qingdao, Shandong 266041, China

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‡

ABSTRACT: The equilibrium solubilities of azoxystrobin, flutriafol, and tebuconazole in subcritical 1,1,1,2-tetrafluoroethane (R134a) were measured using a static method. After tests to confirm the reliability of the experimental apparatus were carried out and the reliability was confirmed, measurements of the solubilities of the three fungicides were implemented at temperatures of 298.15, 313.15, and 333.15 K over the pressure range of 6.0−16.0 MPa. The results indicated that the solubilities increased with increasing pressure under isothermal conditions and increased with increasing temperature at a fixed pressure. To generalize the experimental results, five semiempirical density-based models were employed to correlate the solubility data, including the Chrastil, Kumar and Johnston (K−J), Mendez-Santiago and Teja (M− S−T), Sung and Shim (S−S), and Adachi and Lu (A−L). The measured data showed reasonable agreement with the calculated results from models, for which the average absolute deviation (AARD) in the solubility correlation is from 0.0924 to 4.06%. Additionally, naphthalene has the effect of promoting dissolution as a cosolute in the process of determining the solubilities of fungicides by shorting the equilibrium time.

1. INTRODUCTION Supercritical fluids have a liquid-like density and gas-like viscosity, and their diffusivity is in between the two states, giving them better solvating strength and transport properties.1 Among these supercritical fluids, supercritical carbon dioxide (SCCO2) has been widely studied due to its accessible critical conditions (Tc = 304.15 K, Pc = 7.38 MPa) and higher density than most supercritical fluids.2 However, SCCO2 is a solvent with low polarizability, a low relative dielectric constant, and no dipole moment, which results in its low dissolving capacity for polar solutes, thus further limiting its extensive application, especially for some ionic compounds with high molecular weights.3,4 Fortunately, studies have found that fluorinated hydrocarbon solvents showed better solubilities for polar solutes than SCCO2 due to their higher polarizability and permanent dipole moments.5 As one of the most common fluorinated hydrocarbon solvents, 1,1,1,2-tetrafluoroethane (R134a) is apyrous, nonexplosive, innocuous, nonozonedepleting, nonirritating, noncorrosive, colorless, and tasteless, and it has a relatively slight contribution to global warming.6,7 Meanwhile, the dipole moment of R134a is 2.1 D, and thus, it shows a better dissolving capacity for polar solutes; especially, its critical pressure of 4.06 MPa is easier to achieve, which makes R134a an excellent subcritical fluid solvent.8,9 In principle, it may reduce experimental and operational costs in subcritical R134a extraction, purification, and enzymatic synthetic processes. In recent years, R134a has attracted increasing attention, but studies on the solubility properties of fungicides in this efficient solvent fluid are scarce.10−12 © XXXX American Chemical Society

It has been proven that fungicides can prevent foliar diseases in a wide range of vegetable, field, fruit, and ornamental crops.13 Therefore, they have been widely utilized in the cultivation of agricultural products for the purpose of reducing yield losses.14,15 The three fungicides investigated in this study are azoxystrobin (C22H17N3O5), flutriafol (C16H13F2N3O), and tebuconazole (C16H22ClN3O). Azoxystrobin, methyl (E)-2-{2[6-(2-cyanophenoxy)pyrimidin-4-yloxy]phenyl}-3-methoxyacrylate, is a strobilurin-related fungicide with mitochondrial respiratory complex III as its molecular target.16 Flutriafol, (R,S)-2,4′-difluoro-α-(1H-1,2,4-triazol-1-ylmethyl) benzhydryl alcohol, and tebuconazole, (R,S)-1-p-chlorophenyl-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)pentan-3-ol, are relatively broad-spectrum 1,2,4-triazole fungicides used for the control of fungal diseases by inhibiting the synthesis of ergosterol.17 To ensure the safety of food for consumers, it is necessary to analyze pesticide residues in agricultural products.18 The conventional residue detection methods of pesticides are complicated, time-consuming, and error-prone. Moreover, the use of large amounts of organic solvents causes environment pollution and damages human health. Meanwhile, the solubility of fungicides in SCCO2 or subcritical R134a is one of the most useful thermophysical properties, which should be measured and modeled, and by this means, sample pretreatment technology for residue analysis can be developed with the Received: March 25, 2018 Accepted: June 22, 2018

A

DOI: 10.1021/acs.jced.8b00240 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Basic Information on the Reagents Used in This Work

schematic illustration of the experimental apparatus is shown in Figure 1. It is mainly composed of a high-pressure

cleanup techniques and analytical methods for food samples. Due to the weak dissolving capability of SCCO2 for polar solutes, we only measured the solubilities of three fungicides in subcritical R134a in this work, whose polarizability is slightly higher.19 Generally, two experimental techniques have been used to measure the equilibrium solubility in subcritical fluids, either a dynamic or static method. In this study, a static method, together with high performance liquid chromatography (HPLC) analysis, was established for measuring the equilibrium solubilities of the three fungicides in R134a in a temperature range of 289.15 to 333.15 K and pressures between 6.0 and 16.0 MPa. Repeated measurements were carried out for each experimental condition to obtain results with acceptable standard deviations. The experimental data were correlated using five semiempirical models proposed by Chrastil, K−J, M−S−T, S−S, and A−L, respectively.

Figure 1. Schematic diagram of the static apparatus.

equilibrium vessel with an available volume of 68.5 mL (metal membranes and absorbent cottons were placed in both ends of the cell to prevent entrainment), a U-shaped tube with an effective volume of approximately 4.825 mL, and a methanol-trapping vessel. The volumes of the high-pressure equilibrium vessel and U-shaped tube were obtained by a liquid statics weighing method. Pressure control in the cell was carried out using a buffer tank and a back-pressure regulator with an accuracy of ±0.1 MPa. To ensure that the temperature was constant, the buffer tank, high-pressure equilibrium vessel, and U-shaped tube were immersed in a water bath with an accuracy of ±0.01 K. Before being injected into the buffer tank by a constant-flux syringe pump (2J-XZ, Hangzhou Zhijiang Petrochemical Equipment Co., Ltd., Hangzhou, China), liquid R134a from the inverted cylinder was refrigerated using a cooling bath. Then, through valve 2, the R134a was pressed into the highpressure equilibrium vessel, in which the fungicide was loaded in advance. Valve 3 was used to release the redundant R134a. The temperature was controlled by the water bath, while the pressure of the buffer tank was monitored by a high-precision pressure gauge (P1) with an accuracy of 0.1 MPa. The pressures of the high-pressure equilibrium vessel and the Ushaped tube were monitored by another high-precision

2. EXPERIMENTAL SECTION 2.1. Materials. Liquefied R134a (purity of 99%) was obtained from Mexichem (Mexico). The carbon dioxide was purchased from the Huanyu Gas Company in Qingdao, with a purity of 99%. Naphthalene (purity of 99%) was purchased from Macklin (Shanghai Macklin Biochemical Co. Ltd., Shanghai, China). The chemical purity of methanol was higher than 99.5% (BASF Chemical Co. Ltd., Tianjin Province, China). HPLC-grade methanol was purchased from the Tedia Company, Inc. (Fairfield, USA). The basic information on the fungicides studied in this work is listed in Table 1, including the molecular formula, CAS number, and purity. Fungicides used in this work were purchased from the Le Bang Chemical Co., Ltd. (Shandong, China). All of these reagents were used without further purification. 2.2. Apparatus and Procedure. According to the specific situation of our laboratory, a self-designed static method apparatus was implemented to determine the equilibrium solubilities of the three fungicides in subcritical R134a. The B



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pressure gauge (P2). Before the experiment was started, the valve in the device was slightly opened to ensure that the device was completely free, and the air in the device was exhausted by the R134a in the storage tank. During this period, the flow rate must be controlled to be very small to prevent the solute from being carried into the U-shaped tube. Then, the front and rear valves of the U-shaped tube were closed; the plunger pump was opened; and the appropriate amount of intake air was maintained. After the balance pressure is equilibrated to the preset pressure value, the plunger pump was closed, and after the phase equilibrium was held under the experimental conditions for 300 min (determined by a series of pre-experiments before the formal experiment), the fine-tuning valves 2 and 4 as well as the pump with low flow were opened, followed by R134a being replenished into the buffer tank. A stable pressure in the high-pressure equilibrium vessel was maintained by adjusting valve 2, and the pressure variation during the sampling was ±0.3 MPa. Once the U-shaped tube is full, the value of P2 would rise rapidly; valve 2 was closed; and the pump was stopped immediately. After the U-shaped tube remained stable at the specified pressure, micrometering valve 5 was opened, and the gas in the U-shaped tube was collected by the methanol trapping vessel. After all of the gas in the Ushaped tube was collected, the U-shaped tube was washed with methanol four or five times; the eluate was collected into the methanol trapping vessel and transferred to a 50 mL volumetric flask. The U-shaped tube was dried by nitrogen and left in the fume hood. The volume of R134a was the available volume of the high-pressure equilibrium vessel. Each experimental solubility data point at the same experimental temperature and pressure conditions was determined at least three times to ensure the accuracy, and the reproducibility of each datum was within ±4.6%. 2.3. Preparation. To ensure the reliability of the apparatus and the modified measurement method, experiments were performed to cross-check against binary solubility data in previous literature, which reported the solubility of naphthalene in SCCO2. We measured its solubility at temperatures of 308.15 and 318.15 K and pressures from 8.0 to 14.0 MPa. The samples collected in the U-shaped tube were dissolved in methanol and detected using a UV/vis-752 spectrophotometer (METASH, Shanghai) at 320 nm. In order to obtain reliable data, experiments were performed to determine the equilibrium time at a temperature and pressure of 298.15 K and 6 MPa. The solubilities of each fungicide at various dissolution times were determined separately, and the change in the solubility with the dissolution time was observed. The results are shown in Figure 2. The solubility increased significantly in the first 240 min, but as the equilibrium time further increased, the increase of the solubility was not obvious. When taking both the theoretical optimal equilibrium time and experimental efficiency into consideration, 300 min was chosen as the optimal equilibrium time. After the experiments to ensure the reliability of the apparatus and the modified measurement method were completed, we cleaned the pipeline to avoid the influence of the residue of naphthalene on the solubilities of the fungicides. 2.4. Analytical Method. The composition and quantity of solutes were analyzed by HPLC (Agilent-1260) with a UV−vis detector at 230 nm. The external standard method was adopted to analyze the mass concentrations of fungicides. Separation of the fungicides was achieved on a ZORBAX SBC18 column using water−methanol (30:70 V/V) mixtures at

Figure 2. Determination of the equilibrium time for the static method at 298.15 K and 6.0 MPa: ■, azoxystrobin; red ●, flutriafol; and blue ▲, tebuconazole.

0.7 mL/min at 308.15 K. The injection volume was 20 μL. A group of standard solutions made by dissolving the standards in methanol were analyzed to obtain a calibration curve, and the regression coefficients of azoxystrobin, flutriafol, and tebuconazole were 0.9997, 0.9996, and 0.9994, respectively.

3. RESULTS AND DISCUSSION 3.1. Solubility of Naphthalene in SCCO2. The reliability of the apparatus and modified static method was validated by measuring the binary solubility of naphthalene in SCCO2 at 308.15 and 318.15 K. The measured solubility of naphthalene in SCCO2 in terms of the mole fraction (y) along with the reported results are given in Table 2 and Figure 3.3,20,21 It can be seen from Table 2 that the experimental date shows good agreement with those of the literature, indicating the reliability and accuracy of the experimental apparatus and procedures. 3.2. Solubilities of Fungicides in Subcritical R134a. The experimental data for the solubilities of the fungicides (azoxystrobin, flutriafol, and tebuconazole) in subcritical R134a, together with the R134a density, are listed in Table 3 and Figures 4−6. The density of subcritical R134a is obtained from the National Institute of Standards and Technology Web site.22 The solubilities of the fungicides are expressed as the mole fraction (yi). Figure 4 shows that the experimental solubility of azoxystrobin increases with the increase of pressure at a constant temperature, which could be explained by the increase of the R134a density and the enhancement of the molecular interactions between the solute and R134a molecules. Particularly, the solubility of azoxystrobin increased markedly with increasing pressure at 313.15 K, and a similar solubility was observed at the intersection of the high pressure at 333.15 K. As shown in Figure 5, the trend in the solubility of flutriafol in subcritical R134a with changes in pressure and temperature is similar to that of azoxystrobin. In addition, the influence of temperature on the solubility is more prominent in comparison with the decrease of the density, as the solubility of flutriafol significantly increases with rising temperature, which could be attributed to that the high temperature increased the vapor pressure of the solute.23 As shown in Figure 6, the trend in the solubility of tebuconazole in subcritical R134a with changes in pressure is the same as that of azoxystrobin at C



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Table 2. Comparison of the Solubility Data of Naphthalene in Supercritical CO2 this work

ref 3

ref 20

ref 21

T/K

P/MPa

103y

P/MPa

103y

P/MPa

103y

P/MPa

103y

308.15 308.15 308.15 318.15 318.15 318.15

8.0 10.0 14.0 8.0 10.0 14.0

7.38 10.17 13.38 0.98 7.26

8.0 10.0 14.0 8.5 10.0 14.0

4.8 10.3 13.8 1.2 6.7 17.4

8.8 10.4 13.8 8.5 10.3 13.7

7.8 11.2 13.9 1.1 8.2 16.5

8.05 13.52 15.05 8.49 9.83 15.06

4.4 13.9 14.7 1.1 6.0 20.8

Figure 4. Experimental data for the solubility of azoxystrobin in the tested ranges of pressure and temperature: ■, 298.15 K; red ●, 313.15 K; and blue ▲, 333.15 K.

Figure 3. Mole fraction binary solubility (y) of naphthalene along with the previously reported results. ■, this work at 308.15 K; □, this work at 318.15 K; ★, ref 3 at 308.15 K; ☆, ref 3 at 318.15 K; ●, ref 20 at 308.15 K; ○, ref 20 at 318.15 K; ▲, ref 21 at 308.15 K; and Δ, ref 21 at 308.15 K.

Table 3. Solubility Data of the Three Fungicides in Subcritical R134a azoxystrobin T/K

P/MPa

298.15

6.0 8.0 10.0 12.0 14.0 16.0 6.0 8.0 10.0 12.0 14.0 16.0 6.0 8.0 10.0 12.0 14.0 16.0

313.15

333.15

ρ /g·L a

−1

1235.4 1244.7 1253.3 1261.5 1269.1 1276.4 1182.4 1194.2 1205.0 1214.9 1224.2 1232.9 1102.6 1119.8 1134.9 1148.4 1160.6 1171.8

y1b

4

10

4.57 4.73 5.13 5.50 6.31 6.48 6.95 8.05 9.11 10.63 11.27 11.64 8.93 9.16 10.13 10.83 11.44 11.59

flutriafol

tebuconazole

4

y2b

104y3b

2.50 2.98 3.04 3.18 3.32 3.51 4.83 5.78 6.16 7.31 7.40 7.55 10.72 11.09 11.90 12.61 13.40 14.96

3.35 3.68 3.85 4.03 4.38 4.45 5.17 6.82 6.99 7.28 7.83 8.78 9.11 8.95 8.90 9.59 10.26 10.83

10

Figure 5. Experimental data for the solubility of flutriafol in the tested ranges of pressure and temperature: ■, 298.15 K; red ●, 313.15 K; and blue ▲, 333.15 K.

298.15 and 313.15 K. What makes it different from the other two fungicides is that the dissolution curve of tebuconazole is smooth and slightly decreases before 10 MPa with rising pressure at 333.15 K. Overall, the dissolving capacity of subcritical R134a for the three fungicides increases with increasing pressure. Unexpectedly, it is found that the equilibrium times of the three fungicides were greatly shortened (about 8-fold) due to the trace residues of naphthalene in the experimental pipeline, which is used to

ρ is the density of R134a; values of ρ at different experimental temperatures and pressures were obtained from the NIST fluid property database. bStandard uncertainties for the measured quantities are the following: u(T) = 0.01 K; u(P) = 0.1 MPa; ur(y) = 0.10. a

D



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under the same conditions, the data are shown in Figure 8. It is clear that the ability of subcritical R134a to dissolve

Figure 6. Experimental data for the solubility of tebuconazole in the tested ranges of pressure and temperature: ■, 298.15 K; red ●, 313.15 K; blue ▲, 333.15 K.

Figure 8. Comparison of the solubilities of tebuconazole in SCCO2 and subcritical R134a: black ■, this work at 308.15 K; red ●, this work at 313.15 K; blue ▲, this work at 333.15 K; magenta ★, ref 19 at 323.15 K; and cyan ◆, ref 19 at 338.15 K.

validate the reliability of the apparatus. In order to verify the effect of naphthalene on the solubility of the fungicide, we selected azoxystrobin as the solute because it had a high response and short retention time. One percent naphthalene was added to the balance tank, and the time for the dissolution equilibrium of azoxystrobin in the subcritical R134a to be reached was measured at 298.15 K and 10.0 MPa. The experimental results are shown in Figure 7. It can be seen from

tebuconazole is better than that of SCCO2 within 20 MPa. The reasons for this phenomenon are multiple. On one hand, this may be attributed to the influence of the solvent density. Within the scope of experimental conditions, the density of SCCO2 is between 265.85 and 870.43 g·L−1, while the density of subcritical R134a ranges from 1102.6 to 1235.4 g·L−1. In general, the solvent with a higher density exhibits a higher dissolving capacity. On the other hand, R134a is a polar molecule (dipole moment = 2.1 D), while CO2 is a nonpolar molecule. Due to the principle of “similar is compatible”, tebuconazole as a polar solid solute is more easily dissolved in subcritical R134a with a higher polarity than SCCO2. Furthermore, the molecular volume of R134a is much larger than that of SCCO2, and thus, the average distance between the R134a and tebuconazole molecules may be less than that between the SCCO2 and tebuconazole molecules under the same equilibrium volume loaded with excessive solute, which may lead to the molecular interactions between tebuconazole and R134a to be stronger than those between tebuconazole and SCCO2. Consequently, the solubility of tebuconazole in subcritical R134a is greater than that in SCCO2. 3.4. Correlation of the Solubility Data. Semiempirical density-based models are widely used to predict the behaviors of subcritical and supercritical fluids. The Chrastil, K−J, M− S−T, A−L, and S−S equations are common density-based models for binary systems. Previous reviewed literature elaborated the details of the models used in this work.4 The equations for these models that were used to correlate all of the experimental data for the solubilities of fungicides in subcritical R134a obtained in this study are shown in Table 4. In these models, y is the mole fraction solubility of the three fungicides; ρ (g·L−1) is the density of subcritical R134a; T (K) is the temperature of the system; and P (bar) is the pressure of the system. In the Chrastil and A−L models, S is the mass solubility of the solute in subcritical R134a, which can be calculated using eq 1

Figure 7. Effect of naphthalene on the equilibrium time of azoxystrobin at 298.15 K and 10.0 MPa.

Figure 7 that when naphthalene is present as a cosolute in the subcritical system the solubility of azoxystrobin at 10 min is higher than that at 300 min. At 20 min, the remaining naphthalene in the system still showed solubilization. Considering the entrainer in the SCCO2 extraction process, we speculate that naphthalene acts like an entrainer in the dissolution of fungicides, which forms forces with solute molecules. Alternatively, due to the volatile physical properties of naphthalene and the thick ring structure at the molecular level, the dissolution balance of the solute is accelerated. Therefore, the principle of the solubilization of naphthalene needs to be elaborated in future studies. 3.3. Comparison of the Solubility of the Tebuconazole in SCCO2 and Subcritical R134a. To compare the solubilities of tebuconazole in SCCO2 and subcritical R134a E



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Table 4. Expressions and Results of the Correlations of Data for the Solubilities of the Three Fungicides in Subcritical R134a by Five Semiempirical Models model

expression

a2 T

Chrastil

ln S = a0 + a1 ln ρ +

K−J

ln y = a0 + a1ρ +

M−S−T

T ln(yP) = a0 + a1ρ + a2T

S−S

ln y = a0 +

A−L

ln S = a0 + (e0 + e1ρ + e2ρ2)ln ρ + a1T

S=

a2 T

a y a1 ji + jja 2 + 3 zzzln ρ T T{ k

y·ρ·M2 (1 − y) ·M1

solute azoxystrobin flutriafol tebuconazole azoxystrobin flutriafol tebuconazole azoxystrobin flutriafol tebuconazole azoxystrobin flutriafol tebuconazole azoxystrobin flutriafol tebuconazole

correlation parameters a0 a0 a0 a0 a0 a0 a0 a0 a0 a0 a0 a0 a0 a0 a0

= = = = = = = = = = = = = = =

AARD/%

−57.16, a1 = 10.21, a2 = −4354.2 −41.81, a1 = 8.746, a2 = −6098.6 −38.13, a1 = 7.441, a2 = −4328.2 −2.540, a1 = 7.792·10−3 4.212, a1 = 6.629·10−3, a2 = −6143.9 −0.2248, a1 = 5.748·10−3, a2 = −4408.5 −17242.1, a1 = 7.167, a2 = 24.99 −18496.8, a1 = 6.667, a2 = 30.65 −16847.0, a1 = 6.640, a2 = 25.52 −124.2, a1 = 30901.3, a2 = 52.67, a3 = −14155.3 −20.75, a1 = −1636.9, a2 = 13.24, a3 = −1790.1 −70.54, a1 = 15331.6, a2 = 21.04, a3 = −7912.7 15523.1, e0 = −2701.4, e1 = 0.5984, e2 = −1.415·10−4, a1 = −4909.9 10038.2, e0 = −1743.6, e1 = 0.3839, e2 = −9.016·10−5, a1 = −6618.2 14978.3, e0 = −2604.2, e1 = 0.5737, e2 = −1.350·10−4, a1 = −5016.2

2.65 2.25 4.05 1.30 0.845 1.29 0.166 0.0924 0.127 1.13 0.763 1.20 2.42 1.66 3.27

(1)

where M1 and M2 (g·mol−1) are the molar masses of R134a and the fungicides, respectively. The precision of these models can be expressed by the average absolute relative deviation (AARD), and the AARD was calculated using eq 2 AARD =

n |y − yexptl, i | 100% calcd, i ∑ n i=1 yexptl, i

(2)

where ycalcd,i are the calculated values; yexptl,i are the experimental data; and n is the number of experimental data values. The correlation parameters and corresponding AARDs are listed in Table 4. It is found that all five models are reasonably consistent with the experimental data, and the M−S−T model provides the minimum AARDs among the five models (0.17% for azoxystrobin, 0.09% for flutriafol, and 0.13% for tebuconazole). Usually, the M−S−T model is used to prove the self-consistency of the experimental data. For the M−S−T model correlation, the mole fraction (y) conforms to a single straight line when T ln(yP) − a2T is plotted versus the solvent density (ρ). Figure 9 shows the comparisons of the experimental data and data calculated using the M−S−T model for the three solutes. The plots clearly show that the equilibrium solubilities of the fungicides increase with increasing density in subcritical R134a. Therefore, the selfconsistency of the experimental data is satisfactory. However, the predicted errors were relatively larger at the high-density zone of R134a. Moreover, the value of a1 was obtained from the correlations using the Chrastil, K−J, and M−S−T models, which represent the number of solvent molecules that associate with one solute molecule. Meanwhile, the value of a1 for azoxystrobin is higher than those of the other fungicides, which proves that the interactions between solute and solvent molecules for azoxystrobin are much stronger than those for the other fungicides. Therefore, the solubility of azoxystrobin in R134a is much higher, which is consistent with the experimental phenomenon of this work.

Figure 9. Solubilities of the three fungicides in subcritical R134a correlated using the M−S−T model: black ■, flutriafol, 298.15 K; red ●, flutriafol, 313.15 K; blue ▲, flutriafol, 333.15 K; black ▼, azoxystrobin, 298.15 K; red ◆, azoxystrobin, 313.15 K; blue ★, azoxystrobin, 333.15 K; black +, tebuconazole, 298.15 K; red ×, tebuconazole, 313.15 K; blue *, tebuconazole, 333.15 K; and , calculated using the M−S−T model.

4. CONCLUSION In this work, we designed a static method dissolution apparatus, whose reliability was verified by measuring the solubility of naphthalene in SCCO2. The equilibrium solubilities of the fungicides (azoxystrobin, flutriafol, and tebuconazole) in subcritical R134a were measured for the temperatures of 298.15, 313.15, and 333.15 K in the pressure range from 6.0 to 16.0 MPa. It was found that the equilibrium solubility is highly density-dependent for the three fungicides by comparing the experimental data of different fungicides obtained under the same operational conditions. The Chrastil, K−J, M−S−T, S−S, and A−L models were used to calculate the solubilities of the three fungicides, and the AARDs of these models were in the range of 0.09%−4.06% in subcritical R134a. In addition, the M−S−T model had the best relevance for the three fungicides. Furthermore, we found that naphthalene has the effect of promoting dissolution as a cosolute because the equilibrium times of the three fungicides were greatly shortened due to the trace residues of F



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(13) Battaglin, W. A.; Sandstrom, M. W.; Kuivila, K. M.; Kolpin, D. W.; Meyer, M. T. Occurrence of azoxystrobin, propiconazole, and selected other fungicides in US streams, 2005−2006. Water, Air, Soil Pollut. 2011, 218, 307−322. (14) Fu, Y.; Zheng, Z.; Wei, P.; Wang, M.; Zhu, G.; Liu, Y. Distribution of Thifluzamide, fenoxanil and tebuconazole in rice paddy and dietary risk assessment. Toxicol. Environ. Chem. 2016, 98, 118−127. (15) Edwards, P. G.; Murphy, T. M.; Lydy, M. J. Fate and transport of agriculturally applied fungicidal compounds, azoxystrobin and propiconazole. Chemosphere 2016, 146, 450−457. (16) Rodrigues, E. T.; Lopes, I.; Pardal, M. A. Occurrence, fate and effects of azoxystrobin in aquatic ecosystems: A review. Environ. Int. 2013, 53, 18−28. (17) Zhang, Q.; Hua, X.; Yang, Y.; Yin, W.; Tian, M.; Shi, H.; Wang, M. Stereoselective degradation of flutriafol and tebuconazole in grape. Environ. Sci. Pollut. Res. 2015, 22, 4350−4358. (18) Pareja, L.; Fernández-Alba, A. R.; Cesio, V.; Heinzen, H. Analytical methods for pesticide residues in rice. TrAC, Trends Anal. Chem. 2011, 30, 270−291. (19) Sahle-Demessie, E.; Pillai, U.; Junsophonsri, S.; Levien, K. Solubility of organic biocides in supercritical CO2 and CO2 + cosolvent mixtures. J. Chem. Eng. Data 2003, 48, 541−547. (20) Sahihi, M.; Ghaziaskar, H. S.; Hajebrahimi, M. Solubility of maleic acid in supercritical carbon dioxide. J. Chem. Eng. Data 2010, 55, 2596−2599. (21) Fat’Hi, M. R.; Yamini, Y.; Sharghi, H.; Shamsipur, M. Solubilities of some recently synthesized 1,8-dihydroxy-9,10-anthraquinone derivatives in supercritical carbon dioxide. Talanta 1999, 48, 951−957. (22) NIST Standard Reference Database Number 69; National Institute of Standard and Technology, http://webbook.nist.gov/ chemistry (accessed March 2017). (23) Liu, L.; Li, Z.; Liu, Z.-W.; Liu, Z.-T. Solubilities of l-proline in subcritical HFC-134a and supercritical CO2 fluids. J. Chem. Eng. Data 2009, 54, 2780−2784.

naphthalene. It is necessary to further investigate the principle of naphthalene promoting dissolution, and the application of naphthalene as a cosolute in other experiments will also be a promising research direction.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Tel.: 0532-82031629. Fax: 0532-82031629. ORCID

Yufang Zhao: 0000-0002-3518-5768 Qingyuan Zhao: 0000-0001-5197-1753 Author Contributions §

Y.Z. and Q.Z. contributed equally to this study, and they are cofirst authors of the article. Funding

This work was financially supported by the National Natural Science Funds [Project Number 31071541] and the Program for Changjiang Scholars and Innovative Research Team in University [PCSIRT, IRT1188]. Notes

The authors declare no competing financial interest.

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REFERENCES

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Measurement and Correlation of the Solubilities of Azoxystrobin

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