Solubility of 6-Chloropyridazin-3-amine in Different Solvents

Apr 30, 2012 - The modified Apelblat equation and λh equation were used to ... obtained by the van't Hoff equation, and the change in Gibbs free ener...
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Solubility of 6-Chloropyridazin-3-amine in Different Solvents Xin-Xiang Cao,* Jin-Qiang Liu, Teng-Teng Lv, and Jing-Cai Yao College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang 471022, People's Republic of China ABSTRACT: The solubility of 6-chloropyridazin-3-amine in methanol, ethanol, n-butanol, N,N-dimethylformamide, acetone, cyclohexanone, ethyl acetate, and toluene at temperatures ranging from (298.15 to 343.55) K at atmospheric pressure was obtained using a synthetic method. The results showed that the solubility of 6-chloropyridazin-3-amine in these solvents increases with rising temperature. The modified Apelblat equation and λh equation were used to correlate the experimental solubility respectively. The calculated values with equations showed good consistency with the experimental values, and the root-mean-square relative deviation was less than 4.68 %. The enthalpy of dissolution and entropy of 6-chloropyridazin-3-amine were obtained by the van't Hoff equation, and the change in Gibbs free energy was calculated.

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INTRODUCTION 6-Chloropyridazin-3-amine (molecular formula C4H4ClN3; molecular weight 129.55; CAS Registry Number 5469-69-2) is a very important intermediate for synthesizing benzoylpyridazyl ureas. The pesticides, including benzoylpyridazyl ureas, can inhibit or block the synthesis of chitin of insect larva, leading to the final death of the larvae. Some compounds of benzoylpyridazyl ureas also display good plant growth regulatory activities.1−3 Nowadays, pure 6-chloropyridazin-3-amine is mainly gained by crystallization from the suitable solution.3 For improving and optimizing the crystallization process, it is important for us to know the solubility of 6-chloropyridazin-3-amine in varied kinds of solvents at different temperatures. However, the solubility data of 6-chloropyridazin-3-amine in organic solvents had not been reported. In this work, we present the solubility of the 6chloropyridazin-3-amine in methanol, ethanol, n-butanol, N,N-dimethylformamide, acetone, cyclohexanone, ethyl acetate, and toluene measured from (278.15 to 343.55) K at atmospheric pressure. The modified Apelblat equation and λh equation were used to correlate the experimental solubility values, respectively; the enthalpy of dissolution and entropy of 6-chloropyridazin-3-amine were calculated by the van't Hoff equation, and the change of Gibbs free energy was calculated.

reagent grade and were all purchased from Tianjin Chemical Reagent Co. Ltd., China. The purities of the organic solvents were more than 0.995 mass fraction. Apparatus and Procedure. The solubility of 6-chloropyridazin-3-amine was determined by a synthetic method.4 As shown in Figure 1, our solubility device consisted of a 200 mL

Figure 1. Sketch of the experimental setup for solubility measurements: A, water bath; B, electric magnetic stirrer; C, transistor laser generator; D, photoelectric transformer; E, constant pressure funnel; F, jacketed glass vessel; G, condenser; H, mercury-in-glass thermometer; I, control and digital display.

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EXPERIMENTAL SECTION Materials. 6-Chloropyridazin-3-amine (mass fraction purity > 0.98) supplied by Taizhou Huangyan Dongsheng Pharmaceutical and Chemical Industry Co. Ltd., China, was recrystallized with methanol to get a purified sample. The mass fraction purity of 6-chloropyridazin-3-amine recrystallized was higher than 0.995, determined by high-performance liquid chromatography, HPLC (Shimadzu LC-10AT). The melting point of 6chloropyridazin-3-amine (Tm) was 484.15 K as determined by the melting point apparatus (type OptiMelt MPA100, Stanford Research Systems, Inc., USA). Methanol, ethanol, n-butanol, N,N-dimethylformamide, acetone, cyclohexanone, ethyl acetate, and toluene used in the experiments were all of analytical © 2012 American Chemical Society

jacketed glass vessel, a mercury-in-glass thermometer, a condenser, an electric magnetic stirrer, and a laser beam. The jacketed glass vessel was maintained at a constant temperature by water circulated from a constant-temperature bath (type CS501, China). The mercury-in-glass thermometer (uncertainty of ± 0.05 K, type WLB, China) was inserted into the solution of the vessel to measure the temperature accurately. The condenser was linked to the vessel directly to prevent Received: January 13, 2012 Accepted: April 20, 2012 Published: April 30, 2012 1509

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Table 1. Saturated Mole Fraction Solubility of 6-Chloropyridazin-3-amine in Methanol, Ethanol, n-Butanol, N,NDimethylformamide, Acetone, Cyclohexanone, Ethyl Acetate, and Toluene T/K

103xexptl

103xcalcd,Apel

100(xexptl − xcalcd,Apel)/xexptl

103 xcalcd,λh

100(xexptl − xcalcd,λh)/xexptl

3.7748 4.4665 5.1778 6.0523 7.0241 8.0749 9.4626 10.5422

2.61 −0.67 1.38 0.04 2.63 2.01 −1.11 1.63

2.1352 2.6558 3.2538 3.9781 4.8348 5.8430 7.0242 8.4020 10.0031 11.7379

−3.47 2.06 −2.45 1.73 3.40 2.65 −0.06 0.92 −0.62 −4.17

1.7523 2.3083 3.0690 3.4883 4.2732 5.1068 6.1861 7.4797 8.8737 10.4482

−2.50 −3.25 2.44 2.15 0.26 −2.62 1.65 −0.88 −1.83 −2.09

36.3395 40.7730 45.5023 51.0842 56.6863 63.1412 70.1466 77.7379 84.9528 93.7520

−3.04 −1.64 −0.07 2.05 4.22 2.38 0.51 −1.21 −2.41 −3.67

3.4698 4.1160 4.8583 5.7260 6.6765 7.7778 9.0261

−2.76 2.79 5.38 4.09 2.11 1.72 −3.68

4.5112 5.4152 6.5810 7.7053 9.1679 10.7486 12.7512 14.9168 17.4345

0.90 −2.17 −2.32 1.47 −3.15 −0.46 −1.87 0.77 −0.15

Methanol 298.15 303.35 308.05 313.15 318.15 322.95 328.55 332.45

3.8758 4.4368 5.2504 6.0549 7.2139 8.2409 9.3584 10.7170

± ± ± ± ± ± ± ±

0.0003 0.0012 0.0009 0.0009 0.0010 0.0014 0.0011 0.0007

3.8315 4.5222 5.2345 6.1123 7.0907 8.1510 9.5541 10.6471

298.15 303.25 308.15 313.15 318.15 323.15 328.15 333.15 338.15 342.85

2.0635 2.7116 3.1759 4.0482 5.0048 6.0023 7.0197 8.4798 9.9415 11.2676

± ± ± ± ± ± ± ± ± ±

0.0008 0.0013 0.0010 0.0008 0.0010 0.0009 0.0003 0.0009 0.0012 0.0005

2.0741 2.6383 3.2823 4.0518 4.9436 5.9653 7.1230 8.4212 9.8624 11.3482

296.55 302.95 309.85 313.05 318.25 322.95 328.15 333.45 338.35 343.15

1.7097 2.2356 3.1457 3.5650 4.2842 4.9766 6.2900 7.4142 8.7142 10.2345

± ± ± ± ± ± ± ± ± ±

0.0006 0.0009 0.0008 0.0011 0.0005 0.0010 0.0011 0.0004 0.0009 0.0012

1.7054 2.2843 3.0723 3.5031 4.3015 5.1368 6.1982 7.4408 8.7449 10.1761

298.45 303.35 308.15 313.35 318.15 323.25 328.35 333.45 337.95 343.05

35.2673 40.1148 45.4723 52.1555 59.1862 64.6803 70.5035 76.8059 82.9558 90.4328

± ± ± ± ± ± ± ± ± ±

0.0009 0.0008 0.0004 0.0011 0.0013 0.0010 0.0007 0.0006 0.0010 0.0005

35.1005 40.3850 45.8654 52.0863 58.0327 64.4980 71.0420 77.5885 83.3059 89.6515

298.15 303.15 308.15 313.25 318.15 323.15 328.15

3.3764 4.2339 5.1348 5.9703 6.8206 7.9137 8.7056

± ± ± ± ± ± ±

0.0013 0.0009 0.0008 0.0011 0.0005 0.0004 0.0009

3.3992 4.2048 5.0769 6.0105 6.9220 7.8366 8.7048

298.25 303.25 308.15 313.15 318.25 323.05 328.15 333.15 338.25

4.5522 5.3004 6.4319 7.8199 8.8884 10.6997 12.5177 15.0330 17.4080

± ± ± ± ± ± ± ± ±

0.0008 0.0007 0.0004 0.0011 0.0010 0.0008 0.0009 0.0012 0.0006

4.4988 5.3774 6.5151 7.6173 9.0590 10.6265 12.6254 14.8021 17.3499

1.14 −1.92 0.30 −0.95 1.71 1.09 −2.09 0.65 Ethanol −0.51 2.70 −3.35 −0.09 1.22 0.62 −1.47 0.69 0.80 −0.72 n-Butanol 0.25 −2.18 2.33 1.74 −0.40 −3.22 1.46 −0.36 −0.35 0.57 N,N-Dimethylformamide 0.47 −0.67 −0.86 0.13 1.95 0.28 −0.76 −1.02 −0.42 0.86 Acetone −0.68 0.69 1.13 −0.67 −1.49 0.97 0.01 Cyclohexanone 1.17 −1.45 −1.29 2.59 −1.92 0.68 −0.86 1.54 0.33 1510

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Table 1. continued T/K

103xexptl

103xcalcd,Apel

343.15

19.9725 ± 0.0006

20.1469

298.45 303.35 308.15 313.15 318.25 323.25 328.15 333.15 338.35 343.15

1.3265 1.6572 1.9433 2.2724 2.6328 3.1924 3.5802 4.1304 4.7936 5.3034

± ± ± ± ± ± ± ± ± ±

0.0008 0.0011 0.0004 0.0009 0.0007 0.0005 0.0007 0.0012 0.0004 0.0010

1.3471 1.6218 1.9270 2.2845 2.6925 3.1358 3.6125 4.1419 4.7381 5.3286

298.15 303.25 308.15 313.35 318.15 323.25 328.35 333.15 338.35 343.55

0.0502 0.0673 0.0817 0.1158 0.1552 0.2017 0.2496 0.2930 0.3520 0.4542

± ± ± ± ± ± ± ± ± ±

0.0008 0.0005 0.0007 0.0010 0.0009 0.0013 0.0008 0.0013 0.0010 0.0006

0.0487 0.0595 0.0834 0.1154 0.1516 0.1971 0.2493 0.3039 0.3677 0.4344

100(xexptl − xcalcd,Apel)/xexptl Cyclohexanone −0.87 Ethyl Acetate −1.55 2.14 0.84 −0.53 −2.27 1.77 −0.90 −0.28 1.16 −0.48 Toluene 2.88 11.55 −2.02 0.32 2.29 2.30 0.12 −3.71 −4.43 4.36

103 xcalcd,λh

100(xexptl − xcalcd,λh)/xexptl

20.1802

−1.04

1.3931 1.6471 1.9320 2.2710 2.6663 3.1079 3.5985 4.1648 4.8323 5.5274

−5.02 0.61 0.58 0.06 −1.27 2.65 −0.51 −0.83 −0.81 −4.23

0.0504 0.0669 0.0870 0.1139 0.1451 0.1861 0.2371 0.2958 0.3734 0.4683

−0.47 0.60 −6.42 1.64 6.51 7.72 5.02 −0.94 −6.06 −3.11

Table 2. Parameters of the Modified Apelblat Equation for 6-Chloropyridazin-3-amine in Eight Solvents solvent

A

B

C

100 rmsrdApel

methanol ethanol n-butanol N,N-dimethylformamide acetone cyclohexanone ethyl acetate toluene

−29.8830 143.7066 78.7343 161.5543 440.7384 −36.2946 103.7859 209.2753

−1358.6475 −10345.0322 −7289.6792 −9599.7841 −23280.3180 −1410.5100 −7866.2172 −14560.5060

5.0680 −20.2168 −10.6332 −23.29320 −64.6483 6.2520 −14.7473 −29.9018

1.3654 1.5635 1.6277 0.8869 0.9112 1.4141 1.3676 4.5692

vaporizing of the solvents in the experiment effectively. The electric magnetic stirrer (type 85-2, China) was used to stir continuously for mixing the solid−liquid system sufficiently. The laser beam was employed to monitor the dissolution of the mixtures. The measurement of solubility was due to the fact that, with the dissolution of solute, the intensity of the light transmitting through the solution increases. For each experiment, at the very start predetermined amounts of solvents and solute measured using a Sartorius type BS210S electronic analytical balance (uncertainty of ± 0.0001 g) was added into the jacketed glass vessel. The solid + liquid mixture was being stirred constantly at a fixed temperature. When the solid just disappeared, the light intensity transmitting through the solution in the vessel reached the peak, and an additional solid solute of a certain amount [(2 to 5) mg] was added into the jacketed glass vessel. This process was repeated until the last addition did not completely dissolve in 30 min, and the amount of the solid solute and the total mass of the solvent were recorded. The saturated experimental solubility (xexptl) of 6-chloropyridazin-3amine was obtained by eq 1.

x exptl =

m1/M1 m1/M1 + m2 /M 2

(1)

where m1 and m2 denote the mass of the soild solute 6chloropyridazin-3-amine and the solvent used in experiment and M1 and M2 stand for the molecular weights, respectively. Every data point of the experimental solubility was measured two more times in the experiments, and the relative uncertainty of the data was less than 1 % mole percent.

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RESULTS AND DISCUSSION

The solubility values of 6-chloropyridazin-3-amine in methanol, ethanol, n-butanol, N,N-dimethylformamide, acetone, cyclohexanone, ethyl acetate, and toluene at different temperatures were shown in Table 1, where T is the absolute temperature and xexptl, xcalcd,Apel, and xcalcd,λh are the experimental solubility, calculated data from the Apelblat equation, and the data obtained from the λh equation, respectively. The temperature dependence of the solubility values of 6chloropyridazin-3-amine in different pure solvents was expressed by the modified Apelblat equation and λh equation. The modified Apelblat equation is as:5−8 1511

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Article

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

(2)

where A, B, and C are three adjustable model parameters and T is the absolute temperature. The λh equation is described as follows:9 ⎡⎛ ⎛1 λ(1 − x calcd, λh) ⎞⎤ 1 ⎞ ⎟⎥ = λ h ⎜ − ln⎢⎜1 + ⎟ calcd, λ h ⎢⎣⎝ Tm ⎠ ⎝T x ⎠⎥⎦

(3)

where Tm is the normal fusion temperature of solute 6chloropyridazin-3-amine and λ and h are two adjustable parameters. The values of A, B, and C in the Apelblat equation and the values of λ and h in the λh equation were calculated using the method of the minimum squares and are listed respectively in Tables 2 and 3. The root-mean-square relative deviation (rmsrd) is described as: ⎡ 1 rmsrd = ⎢ ⎢N ⎣

N

∑ ⎜⎜ i=1

2 ⎤1/2 − xiexptl ⎞ ⎥ ⎟⎟ xiexptl ⎠ ⎥⎦

Figure 2. Saturated mole fraction solubility of 6-chloropyridazin-3amine in eight solvents: ▲, methanol; ■, ethanol; □, n-butanol; ▼, N,N-dimethylformamide; ☆, acetone; △, cyclohexanone; ∗, ethyl acetate; ○, toluene; , calculated data from the Apelblat equation; ---, calculated data from the λh equation.

⎛ x calcd i ⎝

(4)

where N represents the number of experimental data points.

Table 4. Values of the Literature Parameters for the Selected Solvents

Table 3. Parameters of the λh Equation for 6Chloropyridazin-3-amine in Eight Solvents solvent

λ

h

100 rmsrdλh

solvent

methanol ethanol n-butanol N,N-dimethylformamide acetone cyclohexanone ethyl acetate toluene

0.1447 0.2968 0.2612 0.4772 0.1671 0.3231 0.0663 0.0309

19742.5571 12959.6127 14727.7574 4276.6478 18133.5829 10315.7656 45733.5200 161603.1028

1.7335 2.5007 2.1333 2.1722 3.4249 1.6824 2.3235 4.6790

methanol ethanol n-butanol N,Ndimethylformamide acetone cyclohexanone ethyl acetate toluene

The comparison between the calculated values of solubility by equations and the data from experiments is represented in Figure 2. From the data listed in Tables 2 and 3, it can be seen that the calculated values of solubility by equations had a good agreement with the experimental data. The root-mean-square relative deviations are no more than 4.57 % with the modified Apelblat equation and less than 4.68 % with the λh equation. So both equations can be applied to correlate the solubility values of 6-chloropyridazin-3-amine in the eight solvents. Table 1 and Figure 2 show the solubility of 6-chloropyridazin-3-amine in all solvents used in this experiment increases with the rising temperature, and the solubility data of 6chloropyridazin-3-amine in different solvents accord with the following order: N,N-dimethylformamide > cyclohexanone > methanol > acetone > ethanol > n-butanol > ethyl acetate > toluene. The values of polarities, dipole moments, dielectric constants, and δ Hildebrand solubility parameters for the selected solvents are listed in Table 4.10 According to Tables 1 and 4 and Figure 2, it was indicated that the sequence of the solubility of 6-chloropyridazin-3-amine in different solvents is consistent with the polarity order of solvents except N,N-dimethylformamide, cyclohexanone, and acetone [polarity: methanol > ethanol > n-butanol > N,Ndimethylformamide > acetone > cyclohexanone > ethyl acetate > toluene]. For the special cases of N,N-dimethylformamide,

polarity

dipole moment

dielectric constant (293.15 K)

solubility parameter

76.2 65.4 60.2 40.4

1.7 1.7 1.66 3.8

32.6 22.4 18.2 36.7

14.5 13.4 11.4 12.1

35.5 28 23 9.9

2.9 3.1 1.7 0.4

20.6 18.2 6.02 2.38

10.0 9.9 9.1 8.9

cyclohexanone, and acetone, it was conjectured that the closer the dipole moments of a solvent and the solute were, the better dissolving capacity of the solute in the solvent was.10 [dipole moment: N,N-dimethylformamide > cyclohexanone > acetone > methanol = ethanol = ethyl acetate > n-butanol > toluene]. Bennema et al.11 studied the correlation between saturated mole fraction solubility of solid solute in an ideal solution and the absolute temperature. It was found that the natural logarithm of saturated mole fraction solubility was a linear function of the inverse of absolute temperature. It was named the van't Hoff equation, and the equation was defined as follows: ΔHfus ΔSfus + (5) RT R 12 Song et al. take into account the nonideal behavior of the real solution; they replaced ΔHfus with enthalpy of dissolution ΔHd and replaced ΔSfus with the entropy of dissolution ΔSd, obtaining the equation as follows: ln x exptl = −

ΔHd ΔSd + (6) RT R The change of Gibbs free energy for the dissolution of 6chloropyridazin-3-amine in different solvents and different ln x exptl = −

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solvents. Similarly, the ΔGd value of 6-chloropyridazin-3-amine in toluene is the largest one, so the solubility of solute in toluene is smallest. These phenomena are all agree with classical thermodynamics theory.

temperatures could be obtained by the Gibbs−Helmholtz equation:13 ΔGd = ΔHd − T ΔSd

(7)

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The plot illustrating the relation between natural logarithm of saturated mole fraction solubility and inverse of absolute temperature is presented in Figure 3. The dissolution enthalpy

CONCLUSIONS The solubility of 6-chloropyridazin-3-amine in eight organic solvents at different temperatures was obtained by a synthetic method and correlated with the Apelblat equation and λh equation. The results show that the correlation results with the two equations are all satisfactory, the correlation results obtained by the Apelblat equation are better than those obtained by the λh equation, and the solubility of 6chloropyridazin-3-amine increases with rising temperature. In addition, the solubility of 6-chloropyridazin-3-amine is particularly large in N,N-dimethylformamide, and changes are even more pronounced with temperature than in the other solvents. The enthalpy of dissolution, entropy, and change of Gibbs free energy of 6-chloropyridazin-3-amine were calculated. The results represent that the dissolution enthalpy relies on the polarity and the dipole moment of the solvents used to a large extent. The order of solubility is consistent with the trend of the results calculated with classical thermodynamics theory.

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Figure 3. Relations between natural logarithm of saturated mole fraction solubility of 6-chloropyridazin-3-amine and reciprocal absolute temperature: ▲, methanol; ■, ethanol; □, n-butanol; ▼, N,Ndimethylformamide; ☆, acetone; △, cyclohexanone; ∗, ethyl acetate; ○, toluene; , calculated data from eq 6.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: 0086-379-65526007. Fax: 0086-379-65523821.

and entropy determined using the method of the least-squares and the change of Gibbs free energy calculated with the values of ΔHd and ΔSd at 278.15 K are listed respectively in Table 5.

Funding

Table 5. Dissolution Enthalpy and Entropy of 6Chloropyridazin-3-amine in Eight Solventsa

Notes

ΔHd solvent methanol ethanol n-butanol N,N-dimethylformamide acetone cyclohexanone ethyl acetate toluene

−1

J·mol

24564.2965 32295.7607 32397.8852 17893.6409 25508.8914 28345.0158 26190.1413 41557.1351

ΔSd −1

We are indebted to the Natural Science Foundation of Henan Province (No. 0511022600 and No. 092102310075) for financial support. The authors declare no competing financial interest.

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ΔGd −1

J·mol ·K

36.0867 57.1978 56.4040 32.3832 38.6369 50.0618 32.9738 57.1970

J·mol−1

REFERENCES

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14526.7809 16386.1926 16709.1126 8886.2538 14762.0377 14420.3261 17018.4788 25647.7896

The values of ΔGd were calculated by the values of ΔHd and ΔSd at 278.15 K. a

From the curves in Figure 3 and the data represented in Tables 4 and 5, it can be seen that the variation tendency of the dissolution enthalpy in different solvents is almost opposite to the trend of the solubility except cyclohexanone and ethyl acetate. So, it was speculated that the dissolution enthalpy to a large extent relied on the polarity and the dipole moment of the solvents as well. It was also found that the orders of the values of ΔGd in different temperature were all exactly opposite to the trend of the solubility. For example, the change of Gibbs free energy for dissolution of 6-chloropyridazin-3-amine in DMF is 8886.2538 J·mol−1 which is much smaller than other values, so the solubility of solute in DMF is much higher than other 1513

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