Solubilities of Bis (2, 4, 6-trimethylbenzoyl) phenylphosphine Oxide in

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Solubilities of Bis(2,4,6-trimethylbenzoyl)phenylphosphine Oxide in Different Organic Solvents at Several Temperatures Zhongwei Wang,* Qing Yu, Ying Liu, Jian Zhao, Zongling Lü, and Jütao Sun School of Material Science & Engineering, Shandong University of Science and Technology, Qingdao 266590, People’s Republic of China ABSTRACT: The mole fraction solubilities of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BPPO) in different organic solvents such as methanol, ethanol, ethyl acetate, cyclohexane, 2-propanol, acetonitrile, n-hexane, dichloromethane, dichloroethane, chloroform, benzene, and toluene were measured at a designated temperature of (295 to 345) K by the gravimetrical method. The solubilities of BPPO in dichloromethane, dichloroethane, chloroform, benzene, and toluene were all higher than 25 g·100 g−1 at 295.4 K. The mole fraction solubilities (x) of BPPO in methanol, ethanol, ethyl acetate, cyclohexane, 2-propanol, acetonitrile, and n-hexane were correlated as a function of temperature. Results showed that the calculated solubilities were in good agreement with the experimental solubility data.

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INTRODUCTION Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BPPO) is a versatile UV photoinitiator for radical polymerization of unsaturated resins, especially pigmented formulations.1−3 It is used as a photoinitiator in synthetic coatings for metal, wood, plastic, paper, optical fibers, as well as printing inks. In industry, BPPO (Figure 1) was synthesized using diphenylphosphine chloride and 2,4,6-trimethylbenzoylchloride

2-propanol, acetonitrile, n-hexane, dichloromethane, dichloroethane, chloroform, benzene, and toluene, were measured by the gravimetrical method. The aim of this study is to provide basic information for the separation, purification, and application of BPPO.

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EXPERIMENTAL SECTION Chemicals Used. BPPO and the solvents used in this study were listed in Table 1. Apparatus and Procedures. The experiments were carried out in a magnetically stirred, jacketed equilibrium cell with the volume of 100 mL as described in the literature.6,7 The equilibrium cell was sealed by a rubber plug to prevent evaporation of the solvent. The temperature of the equilibrium cell was controlled by circulating water from a thermostat (type 501, Shanghai Laboratory Instrument Works Co., Ltd.) within ± 0.05 K. The equilibrium temperature was measured by a thermocouple immersed into the solution which was calibrated against a standard platinum resistance thermometer (SPRT) using a water bath, with an uncertainty of ± 0.1 K. The mass of the samples was determined by an electronic balance (TG328B, Shanghai Instrument Works Co., Ltd.) with the accuracy of ± 0.1 mg. Solubility Measurements. The solubilities of BPPO in methanol, ethanol, ethyl acetate, cyclohexane, 2-propanol, acetonitrile, n-hexane, dichloromethane, dichloroethane, chloroform, benzene, and toluene were measured by the gravimetric method described in the previous work.7 The gravimetric analytical method used in this work was based on evaporation of solvent from a saturated solution sample. The dissolution

Figure 1. Structure of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

as raw materials, and the final product was precipitated from petroleum ether [(333 to 363) K].4,5 To get product with high quality, the crude BPPO was purified with pure or mixed organic solvents, such as petroleum ether, ethyl acetate, cyclohexane, and the mixed aforementioned solvents. On the other hand, in the application process, BPPO always needs to dissolve in some solvents. Thus, the solubility of BPPO in different organic solvents is of great importance for the separation, purification, and application process. To our knowledge, the mole fraction solubilities of BPPO in acetone (0.0204), methanol (0.00204), toluene (0.0482), and butylacetate (0.0164) at 293 K can be found in the commercial introduction of the product (Qingdao Fusilin Chemical Science & Technoloy Co., Ltd.). In this study, the solubilities of BPPO in the different organic solvents, such as methanol, ethanol, ethyl acetate, cyclohexane, © 2012 American Chemical Society

Received: January 8, 2012 Accepted: October 23, 2012 Published: November 5, 2012 3340

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Table 1. Chemical Compounds Used in the Study chemical name

source

initial mole fraction purity

purification method

final mole fraction purity

analysis method

BPPOa methanol ethanol ethyl acetate cyclohexane 2-propanol dichloromethane dichloroethane chloroform benzene toluene acetonitrile n-hexane

Fusilinchemb Finechemc Finechem Finechem Finechem Finechem Finechem Finechem Finechem Finechem Finechem Finechem Finechem

none none none none none none none none none none none none none

-

0.998 0.997 0.998 0.998 0.998 0.997 0.999 0.999 0.998 0.999 0.998 0.998 0.998

HPLCd GCe GC GC GC GC GC GC GC GC GC GC GC

a

BPPO = bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, solid state. bQingdao Fusilin Chemical Science & Technology Co., Ltd. cQingdao Fine Chemical Reagent Co., Ltd. dHigh-performance liquid chromatography. eGas−liquid chromatography.

Table 2. Experimental Mole Fraction Solubility (xexptl) of BPPO in Different Solvents at Varied Temperatures at 0.1 MPa solvent

T/Ka

100xexptlb

δ( × 102)c

methanol

295.4 303.2 308.3 313.1 318.2 323.4 328.0 333.2 295.4 303.2 307.2 313.1 318 324.1 328.3 333.2 295.4 303.2 307.9 313.2 318.2 323.3 328.2 333 338.1 343.2 295.4 303.2 308.3 313.1 318.2 323.4

0.235 0.434 0.629 0.909 1.342 1.950 2.825 4.265 0.372 0.627 0.827 1.193 1.609 2.389 3.258 4.715 1.781 2.589 3.264 4.059 5.077 6.395 8.424 10.286 12.684 16.019 0.160 0.2391 0.323 0.414 0.542 0.7323

0.086 0.095 0.116 0.215 0.156 0.136 0.126 0.236 0.115 0.132 0.098 0.126 0.206 0.213 0.263 0.185 0.104 0.156 0.207 0.156 0.154 0.209 0.225 0.308 0.206 0.254 0.065 0.085 0.069 0.098 0.125 0.203

ethanol

ethyl acetate

cyclohexane

a

solvent

2-propanol

acetonitrile

n-hexane

T/Ka

100xexptlb

δ( × 102)c

328.1 333.2 338.1 343.3 295.4 305.2 308.2 313.3 318 324.1 328.1 333.2 338.3 343.2 295.4 303.2 308 313.3 318.1 323.2 328.1 333.2 338.1 295.4 303.2 308.1 313.2 318.1 322.9 328.1 333.2

0.966 1.227 1.704 2.171 0.278 0.550 0.680 0.980 1.372 2.053 2.809 3.999 5.557 7.933 0.463 0.793 1.081 1.541 2.253 3.001 4.209 6.113 8.630 0.151 0.218 0.277 0.323 0.389 0.442 0.525 0.635

0.156 0.226 0.214 0.197 0.087 0.124 0.156 0.185 0.256 0.185 0.264 0.185 0.185 0.213 0.112 0.116 0.215 0.212 0.139 0.184 0.264 0.195 0.232 0.114 0.126 0.098 0.085 0.156 0.203 0.096 0.135

Relative uncertainty for x; ur(x) = 0.02. bUncertainty for T; u(T) = 0.1 K. cRoot-mean-square deviations; δ = ((∑ni (xi − x)̅ 2)/(n − 1)).

where m1 and m2 represent the mass of the BPPO and solvent, respectively, and M1 and M2 are the respective molecular masses. The average value was taken from three measurements at each temperature.

process of BPPO in the varied solvents was the same as that described in the previous paper.7 It was found that 2 h is enough for the equilibrium of each measurement. The mole fraction solubility of BPPO in different pure solvents could be calculated by the following equation x

exptl

m1/M1 = m1/M1 + m2 /M 2

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RESULTS AND DISCUSSION At first, methanol, ethanol, ethyl acetate, cyclohexane, 2-propanol, acetonitrile, n-hexane, dichloromethane, dichloroethane, chloroform,

(1) 3341

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Table 3. Regressed Parameters A, B, and C and the Absolute Average Deviation (AAD) of the Measured Solubility from the Calculated Results of Equation 3

benzene, and toluene were selected as solvents. The tests for solubilities were carried out to find whether BPPO can be readily dissolved in the solvents or not. It was found that BPPO is readily dissolved in dichloromethane, dichloroethane, chloroform, benzene, and toluene, and the solubilities in these five solvents were all higher than 25 g·100 g−1 at 295.4 K, which means they are good solvents for BPPO. This may benefit the application when using these as solvents. Meanwhile, the solubilities in methanol, ethanol, ethyl acetate, cyclohexane, 2-propanol, acetonitrile, and n-hexane were measured at various temperatures. The mole fraction solubilities of BPPO in the selected solvents of methanol, ethanol, ethyl acetate, cyclohexane, 2-propanol, acetonitrile, and n-hexane at designed temperatures were listed in Table 2 and graphically shown in Figure 2. The root-mean-square deviations (δ), presented in Table 2, are defined as follows

i

−436.6889 −443.8260 −158.8680 −262.7223 −171.9030 −406.4037 205.6647

13613.7508 14788.0307 3303.6377 7303.8143 1787.8602 12925.4592 −12923.4676

67.6014 68.2375 25.2503 40.7012 28.1138 62.8068 −29.6045

2.0 2.5 1.8 2.2 1.3 2.0 1.7

AUTHOR INFORMATION

This work was financially supported by Innovation Fund for Technology Based Firms (11C26213715128), Foundation of Shandong Provincial Education Department (J06D03), and Foundation of Science and Technology Bureau in Qingdao Economic & Technology Development Zone (2009-2-37, 2011-2-38).

(3)

Notes

The authors declare no competing financial interest.

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xiexptl − xical xiexptl

methanol ethanol ethyl acetate cyclohexane 2-propanol acetonitrile n-hexane

Funding

The parameters A, B, and C for the solvents are listed in Table 3. The absolute average deviations (AADs) of the measured solubility from the correlated data are also listed in Table 3. The AAD is defined as

∑

100 AAD

*E-mail: [email protected]. Fax: 86-53286057573.

where xi is the experimental value; x̅ is the average value of experimental data; and n is the number of data points for each temperature. The mole fraction solubilities (x) of BPPO were correlated as a function of temperature according to eq 3.

1 AAD = N

C

Corresponding Author

(2)

ln(x) = A + B /(T /K) + C*ln(T /K)

B

■

n

∑i (xi − x ̅ )2 n−1

A

with the increase of temperature. The slope of the temperature dependence of the solubility varied for different solvents used. The order of such slopes is n-hexane < cyclohexane < 2-propanol < ethanol < methanol < acetonitrile < ethyl acetate. Comparing the solubility difference between 295.4 K and the temperature near the boiling point of the selected solvents, acetonitrile showed the highest solubility difference which is comparable with that of ethyl acetate. The high solubility difference for the two solvents will benefit in the purification process of BPPO when these solvents are used for a recrystallization. At low temperature, the solubilities decreased in the order: ethyl acetate, acetonitrile, methanol, ethanol, 2-propanol, cyclohexane, and n-hexane, respectively. However, the order of the solubilities changed at about (323 and 330) K. It was rather unexpected to find that the solubility of BPPO showed no apparent relationship to the polar properties of the solvents. For example, BPPO is readily soluble in such nonpolar solvent as benzene, but it is not easy to dissolve in other nonpolar solvents such as cyclohexane and n-hexane. On the other hand, BPPO is easy to dissolve in benzene as well as in chloroform, which have quite different polarities. Using methanol as solvent, the solubility of BPPO at 293 K can be calculated from the correlation function, and the result is 0.00195, which is comparable with the commercial information of 0.00204.

Figure 2. Temperature dependence of ln(x) in ethyl acetate (▲), acetonitrile (▶), methanol (■), ethanol (●), 2-propanol (◀), cyclohexane (▼), n-hexane (⧫), and the correlated data with eq 3 (−).

δ=

solvent

REFERENCES

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(4)

where the superscript exptl stands for the experimental data; cal stands for the correlated values; and N is the number of data points. The results showed that for all selected solvents, in the whole temperature range, the solubilities of BPPO could be correlated by eq 3 with the overall absolute average deviation below 2.5 %. The experimental data showed that the mole fraction solubilities of BPPO in diverse solvents differed greatly from each other, and the solubilities of BPPO in different solvents increased smoothly 3342

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(5) Ellrich, K.; Herzi. C. Bisacylphosphine oxides, the preparation and use there of. USP 4792632, 1988. 12.20. (6) Zhu, M. Solubility and Density of the Disodium Salt Hemiheptahydrate of Ceftriaxone in Water + Ethanol Mixtures. J. Chem. Eng. Data 2001, 46, 175−176. (7) Gao, J.; Wang, Z. W.; Xu, D. M.; Zhang, R. K. Solubilities of Triphenylphosphine in Ethanol, 2-Propanol, Acetone, Benzene, and Toluene. J. Chem. Eng. Data 2007, 52, 189−191.

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