Process for the preparation of aryl silicon compounds by iron catalyzed aryl ether carbon-oxygen bond cleavage and reaction with chlorosilanes

Abstract

The application provides a preparation method for synthesizing aryl silicon compounds by iron catalysis of aryl ether carbon-oxygen bond cleavage and chlorosilane reaction, and solves the technical problems that the existing aryl silicon compound preparation method is not environmentally friendly and lacks stable carbon electrophiles. The application is specifically as follows: under an inert atmosphere, aryl ether, chlorosilane and an iron catalyst are added into an organic solvent, a Grignard reagent is dropped, stirring is carried out at room temperature, and after the reaction is completed, quenching is carried out, and aryl silicon compounds are obtained through separation and purification.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of arylsilicon compound synthesis, and particularly relates to a method for synthesizing arylsilicon compounds by iron-catalyzed aryl ether carbon-oxygen bond cleavage and chlorosilane reaction. BACKGROUND

[0002] Arylsilicon compounds are important synthetic intermediates and are widely used in the fields of pharmaceutical chemistry, material chemistry, organic synthetic chemistry, etc. For example, the introduction of silicon groups into drug molecules makes them have stronger efficacy, higher selectivity and smaller toxic side effects; in the field of materials, arylsilicon compounds are also precursors of many high-temperature ceramics; at the same time, in organic synthesis, carbon-silicon bonds can undergo a series of transformations to realize the construction of new carbon-carbon bonds and carbon-heteroatom bonds, such as carbon-halogen, carbon-nitrogen, carbon-oxygen, carbon-boron bonds, etc. This multifunctional transformation makes it an important intermediate for synthetic design, realizing the synthesis of other functional molecules and materials.

[0003] In the current method for preparing arylsilicon compounds, catalytic coupling reaction of silicon electrophiles is an important strategy for constructing C(aryl)-Si bond. Although there are currently a variety of catalysts for the coupling of silicon electrophiles with carbon nucleophiles, the reductive coupling of silicon electrophiles with carbon electrophiles in the process of C(aryl)-Si bond formation is still a great challenge. In order to solve this challenge, Chinese patent CN111518125B discloses a method for preparing arylsilicon compounds by nickel-catalyzed Si-Cl bond cleavage, reductive cross-coupling of chlorosilane with vinyl and aryl triflate / halide. The aryl triflate / halide used in this method will generate toxic halide waste in the reaction, and its stability is not high, so there is still a lack of more environmentally friendly and stable carbon electrophiles in the strategy for constructing C(aryl)-Si bond.

[0004] In view of the application prospect of arylsilicon compounds and the problems existing in the current preparation process, it is necessary to explore a new method for preparing arylsilicon compounds. SUMMARY

[0005] The present application aims to solve the technical problems of the existing arylsilicon compound preparation method, which is not environmentally friendly and lacks stable carbon electrophiles, and provides a preparation method for synthesizing arylsilicon compounds by iron-catalyzed aryl ether carbon-oxygen bond cleavage and chlorosilane reaction.

[0006] The concept of the present application is:

[0007] The research team of the present application reselects carbon electrophiles, discards the conventional synthesis route through C(aryl)-C and Si-Cl bond activation, and synthesizes arylsilicon compounds through the route of strong electrophilic C(aryl)-O and Si-Cl bond activation.

[0008] Aryl ether structural units have abundant C(aryl)-O, which are widely present in bioactive molecules (such as Figure 1 As the simplest derivative of phenol, aryl ether generates less, relatively non-toxic waste when participating in a reaction, and has better stability than aryl bromide and aryl iodide, so the research team of the present application intends to select aryl ether as a carbon electrophile to provide aryl groups; a silicon electrophile is intended to be selected as chlorosilane to perform a catalytic coupling reaction, which is more abundant and cheaper than silicon organometallic reagents and hydrosilanes; a catalyst is intended to be selected as a low-valent iron catalyst which exhibits unique activity and selectivity in the coupling reaction of various non-active carbon electrophiles (for example, coupling of aryl esters and ethers by activating C(aryl)-O bonds), while studying the potential of cross-electrophilic coupling between two strong electrophilic C(aryl)-O and Si-Cl bonds, realizing the reductive cross-coupling of diaryl ether and chlorosilane, and providing a new idea for organosilicon chemistry.

[0009] To achieve the above-mentioned purposes, the technical solutions provided by the present application are as follows:

[0010] A preparation method of an aryl silicon compound, which is characterized by synthesis through iron-catalyzed aryl ether carbon-oxygen bond cleavage and chlorosilane reaction, specifically comprising the following steps:

[0011] Under an inert atmosphere (such as argon), aryl ether, chlorosilane and iron catalyst are added to an organic solvent, and Grignard reagent is dropped, and the reaction is carried out by stirring at room temperature, and after the reaction is completed, quenching is performed (quenching is performed using saturated aqueous ammonium chloride solution), and the aryl silicon compound is obtained by separation and purification; the synthesis general formula is as follows:

[0012]

[0013] wherein, R 1 , R 2 , R 3 are aliphatic groups or aromatic groups.

[0014] Further, the specific operation of separation and purification is first extracted with ethyl acetate, then dried with anhydrous Na2SO4, filtered, and the organic solvent is removed under reduced pressure, and finally the aryl silicon compound is purified by 1:3-5:4-8 column chromatography (fast silica gel column, with ethyl acetate: petroleum ether = 1:10-20 as developing agent).

[0015] Further, the molar ratio of the aryl ether, chlorosilane and Grignard reagent is 1:3-5:4-8, preferably 1:3:4;

[0016] The amount of the organic solvent is 3-5 times the molar amount of the aryl ether.

[0017] The amount of the iron catalyst is 5-10% of the molar amount of the aryl ether;

[0018] Further, the reaction time is 24-48h;

[0019] In order to grasp the reaction process in real time, thin layer chromatography (TLC) is used to track the reaction process.

[0020] Further, the Grignard reagent is isobutylmagnesium chloride, isopropylmagnesium chloride, tert-butylmagnesium chloride, magnesium chloride, phenylmagnesium chloride or cyclohexylmagnesium chloride;

[0021] The iron catalyst is ferric chloride, ferrous chloride, iron triflate or iron acetylacetone;

[0022] The organic solvent is tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, toluene, n-hexane, 1,4-dioxane, 1,2-dichloroethane or nitromethane.

[0023] Further, when the aryl ether is a compound of formula I and the chlorosilane is n-butyl dimethyl chlorosilane, the aryl silicon compound is a compound of formula I';

[0024]

[0025] In formulae I and I', R is cyclohexyl, cyclopentyl, cycloheptyl, methyl, isopropyl, tert-butyl, adamantyl, phenyl, p-methoxyphenyl or p-fluorophenyl.

[0026] Further, when the aryl ether is a compound of formula II and the chlorosilane is n-butyl dimethyl chlorosilane, the aryl silicon compound is a compound of formula II';

[0027]

[0028] In formulae II and II', R is 2-methyl, 2-isopropyl, 2-propenyl, 2-phenyl, 2-methoxy, 2-benzyl, 3-methyl, 3-trifluoromethyl, 4-methyl, 4-tert-butyl, 4-methoxy, 4-phenyl or 4-fluoro.

[0029] Further, when the aryl ether is a compound of formula III and the chlorosilane is n-butyl dimethyl chlorosilane, the aryl silicon compound is a compound of formula III';

[0030]

[0031] In formulae III and III', R is cyclohexyl or phenyl, and R1 is methyl or methoxy.

[0032] Further, when the chlorosilane is a compound of formula IV and the aryl ether is a compound of formula V, the aryl silicon compound is a compound of formula IV';

[0033]

[0034] In formulas IV and IV', R, R', and R" are methyl, ethyl, isopropyl, phenyl, trifluoropropyl, vinyl, or hydrogen.

[0035] In addition, the present invention also provides aryl silicon compounds obtained by the above preparation method.

[0036] Advantages of this invention:

[0037] This invention uses aryl ethers and chlorosilanes as raw materials, Grignard reagents as reducing agents, and iron catalysts to synthesize arylsilane compounds. The target product is synthesized through a pathway activated by strongly electrophilic C(aryl)-O and Si-Cl bonds. Aryl ethers, as the simplest derivatives of phenol, are highly stable and, compared to aryl iodine and aryl bromide, do not produce toxic waste during the reaction, making them environmentally friendly. Chlorosilanes are cheaper and more readily available than organometallic reagents and hydrosilanes. Grignard reagents and transition metal iron catalysts are reactive, inexpensive (significantly reducing costs compared to the nickel-based catalysts used in the prior art patents), and have high yields. The entire preparation method uses readily available raw materials, is easy to operate, and yields considerable results. The synthesis of arylsilane compounds, which play an important role in pharmaceutical chemistry, materials chemistry, and organic synthesis chemistry, has promising application prospects. Attached Figure Description

[0038] Figure 1 These are representative biologically active molecules containing multiple aryl CO groups. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0040] Example 1

[0041]

[0042] Under an argon atmosphere, N-cyclohexylbenzamide-2-phenyl ether (0.4 mmol), n-butyldimethylchlorosilane (1.2 mmol), and FeCl2 (0.04 mmol) were added to tetrahydrofuran (1.0 mL). Isobutylmagnesium chloride solution (1.6 mmol) was slowly added dropwise, and the resulting solution was stirred at room temperature for 24 hours. The reaction was quenched with saturated ammonium chloride aqueous solution, and the mixture was extracted with ethyl acetate (3 times, 10 mL each time). The extracts were combined, dried over anhydrous sodium sulfate, filtered, and the organic solvent was removed under reduced pressure. The product was separated by silica gel column chromatography using petroleum ether:ethyl acetate = 20:1 as the developing solvent, with a yield of 75%. Spectral data of the obtained product: 1H NMR (400 MHz, CDC13) δ 7.64 - 7.57 (m, 1H), 7.42 - 7.31 (m, 3H), 5.82 (br s, 1H), 4.42 - 4.30 (m, 1H), 2.15 - 2.02 (m, 2H), 1.74 - 1.63 (m, 4H), 1.52 - 1.43 (m, 2H), 1.34 - 1.22 (m, 4H), 0.86 (dd, J = 15.0, 8.1 Hz, 5H), 0.30 (s, 6H). 13 CNMR (125 MHz, CDC13) δ 170.3, 142.9, 138.9, 135.6, 129.1, 128.5, 126.0, 48.6, 33.2, 26.6, 26.4, 25.5, 24.8, 15.9, 13.8, -1.8. HRMS (ESI + ): calcd for C 19 H 32 SiNO[M+H] + 318.22532, found 318.22489.

[0043] Example 2

[0044]

[0045] N-cyclopentylbenzamide-2-phenyl ether (0.4 mmol), n-butyl dimethyl chlorosilane (1.2 mmol), FeCl2(0.02 mmol) were added into tetrahydrofuran (1.0 mL) under argon atmosphere, isopropyl magnesium chloride solution (1.6 mmol) was added dropwise slowly, the resulting solution was stirred at room temperature for 24 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extracts, dried with anhydrous sodium sulfate, filtered, removed the organic solvent under reduced pressure, separated by silica gel column chromatography with petroleum ether: ethyl acetate = 20: 1 as developing agent, the product was obtained with a yield of 64%. The product obtained had the following spectral data: 1 H NMR (400 MHz, CDC13) δ 7.64 - 7.57 (m, 1H), 7.42 - 7.31 (m, 3H), 5.82 (br s, 1H), 4.42 - 4.30 (m, 1H), 2.15 - 2.02 (m, 2H), 1.74 - 1.63 (m, 4H), 1.52 - 1.43 (m, 2H), 1.34 - 1.22 (m, 4H), 0.86 (dd, J = 15.0, 8.1 Hz, 5H), 0.30 (s, 6H). 13C NMR (100 MHz, CDC13) δ 170.9, 142.8, 138.8, 135.6, 129.2, 128.5, 126.0, 51.67, 33.1, 26.6, 26.4, 23.6, 15.9, 13.8, -1.8. HRMS (ESI): calcd for C + ): calcd for C 18 H 30 SiNO[M+H] + 304.20967, found 304.20895.

[0046] Example 3

[0047]

[0048] N-phenylbenzamide-2-phenyl ether (0.4 mmol), n-butyl dimethyl chlorosilane (1.6 mmol), FeCl3(0.04 mmol) were added to tetrahydrofuran (1.0 mL) under argon atmosphere, after slowly dropping tert-butyl magnesium chloride solution (2.0 mmol), the resulting solution was stirred at room temperature for 24 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extracts, added anhydrous sodium sulfate to dry, filtered, removed the organic solvent under reduced pressure, separated by flash silica gel column chromatography with petroleum ether: ethyl acetate = 15:1 as developing agent, the product was obtained with a yield of 60%. The product obtained the following data: 1 H NMR (400 MHz, CDC13) δ 7.65 (dd, J = 23.0, 7.2 Hz, 4H), 7.53 (d, J = 7.3 Hz, 1H), 7.49 - 7.44 (m, 1H), 7.42 - 7.33 (m, 3H), 7.16 (t, J = 7.4 Hz, 1H), 1.34 - 1.26 (m, 4H), 0.92 - 0.82 (m, 5H), 0.33 (s, 6H). 13 C NMR (100 MHz, CDC13) δ 169.3, 142.8, 138.8, 138.0, 135.7, 129.5, 129.1, 128.7, 126.0, 124.4, 120.0, 26.5, 26.3, 15.8, 13.8, -1.8.

[0049] Example 4

[0050]

[0051] N-phenyl-4-methoxybenzamide-2-phenyl ether (0.4 mmol), n-butyl dimethyl chlorosilane (2.0 mmol), FeCl2(0.02 mmol) were added to tetrahydrofuran (1.0 mL), after slowly dropping phenyl magnesium chloride solution (1.6 mmol), the resulting solution was stirred at room temperature for 36 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extract, added anhydrous sodium sulfate to dry, filtered, removed the organic solvent under reduced pressure, separated by silica gel column chromatography with petroleum ether: ethyl acetate = 20:1 as developing agent, the product was obtained with a yield of 80%. The product obtained the wave data: 1 H NMR (400 MHz, CDC13) δ 7.67 - 7.53 (m, 4H), 7.36 (t, J = 7.9 Hz, 2H), 7.15 (t, J = 7.4 Hz, 1H), 7.09 (d, J = 2.3 Hz, 1H), 7.00 (dd, J = 8.3, 2.5 Hz, 1H), 3.82 (s, 3H), 1.33 - 1.25 (m, 4H), 0.90 - 0.81 (m, 5H), 0.30 (s, 6H). 13 C NMR (100 MHz, CDC13) δ 169.0, 159.9, 144.4, 137.9, 137.2, 129.1, 124.5, 119.8, 114.7, 112.5, 55.2, 26.5, 26.3, 16.0, 13.8, -1.7.

[0052] Example 5

[0053]

[0054] N-phenyl-5-methylbenzamide-2-phenyl ether (0.4 mmol), n-butyl dimethyl chlorosilane (1.2 mmol), FeCl2(0.02 mmol) were added to 2-methyl tetrahydrofuran (1.0 mL), after slowly dropping magnesium chloride solution (3.2 mmol), the resulting solution was stirred at room temperature for 36 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extract, added anhydrous sodium sulfate to dry, filtered, removed the organic solvent under reduced pressure, separated by silica gel column chromatography with petroleum ether: ethyl acetate = 20:1 as developing agent, the product was obtained with a yield of 75%. The product obtained the wave data: 1H NMR (400 MHz, CDC13) δ 7.70 (br s, 1 H), 7.62 (d, J = 7.9 Hz, 2 H), 7.49 (s, 1 H), 7.45 (d, J = 7.7 Hz, 1 H), 7.36 (t, J = 7.9 Hz, 2 H), 7.21 - 7.13 (m, 2 H), 2.43 (s, 3 H), 1.37 - 1.29 (m, 4 H), 0.94 - 0.85 (m, 5 H), 0.35 (s, 6 H). 13 C NMR (100 MHz, CDC13) δ 169.3, 140.0, 139.3, 138.9, 138.1, 136.5, 129.2, 129.0, 126.1, 124.3, 119.9, 26.5, 26.3, 21.5, 15.9, 13.7, -1.7.

[0055] Example 6

[0056]

[0057] N-phenyl-4-methylbenzamide-2-phenyl ether (0.4 mmol), n-butyl dimethyl chlorosilane (1.2 mmol), FeCl2(0.04 mmol) were added into toluene (1.0 mL), after slowly dropping isopropyl magnesium chloride solution (1.6 mmol), the resulting solution was stirred at room temperature for 36 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extracts, added anhydrous sodium sulfate to dry, filtered, removed the organic solvent under reduced pressure, separated by silica gel column chromatography with petroleum ether: ethyl acetate = 20:1 as developing agent, the product was obtained with a yield of 77%. The product obtained: 1 H NMR (400 MHz, CDC13) δ 7.67 - 7.54 (m, 4 H), 7.37 (dd, J = 9.7, 6.1 Hz, 3 H), 7.29 (d, J = 7.6 Hz, 1 H), 7.16 (t, J = 7.4 Hz, 1 H), 2.39 (s, 3 H), 1.35 - 1.26 (m, 4 H), 0.92 - 0.82 (m, 5 H), 0.32 (s, 6 H). 13 C NMR (100 MHz, CDC13) δ 169.4, 142.9, 138.8, 138.0, 135.7, 135.0, 130.2, 129.0, 126.9, 124.3, 119.8, 26.5, 26.3, 21.1, 15.9, 13.7, -1.8.

[0058] Example 7

[0059]

[0060] N-cyclohexyl-4-methoxybenzamide-2-phenyl ether (0.4 mmol), n- butyldimethylchlorosilane (1.2 mmol), FeCl2(0.04 mmol) were added to tetrahydrofuran (1.0 mL) under argon atmosphere, isopropylmagnesium chloride solution (1.6 mmol) was added dropwise slowly, the resulting solution was stirred at room temperature for 48 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extracts, dried over anhydrous sodium sulfate, filtered, removed the organic solvent under reduced pressure, separated by silica gel column chromatography with petroleum ether: ethyl acetate = 20: 1 as developing agent to obtain the product, the yield was 77%. The product obtained the wave data: 1 H NMR (500 MHz, CDC13) δ 7.50 (d, J = 8.2 Hz, 1H), 6.96 - 6.88 (m, 2H), 5.77 (br s, 1H), 3.94 - 3.87 (m, 1H), 3.79 (s, 3H), 2.06 - 1.98 (m, 2H), 1.76 - 1.69 (m, 2H), 1.63 (dd, J = 9.3, 3.9 Hz, 1H), 1.44 - 1.36 (m, 2H), 1.33 - 1.16 (m, 7H), 0.88 - 0.81 (m, 5H), 0.27 (s, 6H). 13 CNMR (100 MHz, CDC13) δ 170.0, 159.8, 144.5, 137.0, 129.2, 113.8, 112.9, 55.1, 48.6, 33.1, 26.5, 26.4, 25.5, 24.8, 16.0, 13.8, -1.7.

[0061] Example 8

[0062]

[0063] N-cyclohexylbenzamide-2-phenyl ether (0.4 mmol), methyldiphenylchlorosilane (1.2 mmol), FeCl2(0.04 mmol) were added to tetrahydrofuran (1.0 mL) under argon atmosphere, isopropylmagnesium chloride solution (1.6 mmol) was added dropwise slowly, the resulting solution was stirred at room temperature for 48 hours, saturated aqueous ammonium chloride solution was added to quench the reaction, extracted with ethyl acetate (3 times, 10 mL each time), combined the extracts, dried over anhydrous sodium sulfate, filtered, removed the organic solvent under reduced pressure, separated by silica gel column chromatography with petroleum ether: ethyl acetate = 20: 1 as developing agent to obtain the product, the yield was 65%. The product obtained the wave data: 1H NMR (500 MHz, CDCI3) δ 7.52 (dd, J = 8.5, 2.3 Hz, 4H), 7.44 - 7.31 (m, 10H), 5.62 (br s, 1 H), 3.61 - 3.50 (m, 1 H), 1.70 - 1.54 (m, 5H), 1.32 - 1.25 (m, 2H), 1.1 1 - 1.04 (m, 1 H), 0.99 (s, 3H), 0.90 - 0.80 (m, 2H). 13 C NMR (125 MHz, CDCI3) δ 169.5, 143.6, 138.1, 137.4, 134.9, 134.7, 133.9, 129.6, 129.4, 129.1, 128.9, 127.7, 126.7, 48.5, 32.4, 25.4, 24.6, -2.6.

[0064] In addition to the above examples, other aryl ethers can be used as starting materials to prepare corresponding aryl silicon compounds using the method of the present application. Specifically, under an inert atmosphere, the aryl ether, chlorosilane and iron catalyst are added to an organic solvent, and Grignard reagent is added dropwise. The reaction is stirred at room temperature for 24-48 h. After the reaction is completed, it is quenched, separated and purified to obtain the corresponding aryl silicon compound.

[0065] The above description is merely a specific implementation of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the scope of the present application, and these modifications or replacements should be included in the scope of protection of the present application.

Claims

1. A method for preparing an arylsilyl compound, characterized in that: Under an inert atmosphere, aryl ethers, chlorosilanes and iron catalysts were added to an organic solvent, Grignard reagent was added dropwise, and the reaction was carried out by stirring at room temperature. After the reaction was completed, the reaction was quenched, and the arylsilane compounds were obtained by separation and purification. The Grignard reagent is isobutyl magnesium chloride, isopropyl magnesium chloride, tert-butyl magnesium chloride, magnesium chloride, or phenyl magnesium chloride; The iron catalyst is ferric chloride or ferrous chloride; The general formula for synthesis is: The aryl ether is a compound of formula I, the chlorosilane is n-butyldimethylchlorosilane, and the aryl silicon compound is a compound of formula I'. In formulas I and I', R is cyclohexyl, cyclopentyl, cycloheptyl, methyl, isopropyl, tert-butyl, adamantyl, phenyl, p-methoxyphenyl, or p-fluorophenyl; Alternatively, the aryl ether is a compound of formula II, the chlorosilane is n-butyldimethylchlorosilane, and the aryl silicon compound is a compound of formula II'. In formulas II and II', R is 2-methyl, 2-isopropyl, 2-propenyl, 2-phenyl, 2-methoxy, 2-benzyl, 3-methyl, 3-trifluoromethyl, 4-methyl, 4-tert-butyl, 4-methoxy, 4-phenyl, or 4-fluoro. Alternatively, the aryl ether is a compound of formula III, the chlorosilane is n-butyldimethylchlorosilane, and the arylsilane is a compound of formula III'. In formulas III and III', R is cyclohexyl or phenyl, and R1 is methyl or methoxy; Alternatively, the chlorosilane is a compound of formula IV, the aryl ether is a compound of formula V, and the arylsilane is a compound of formula IV'; In formulas IV and IV', R, R', and R" are methyl, ethyl, isopropyl, phenyl, trifluoropropyl, vinyl, or hydrogen.

2. The preparation method according to claim 1, characterized in that: The specific separation and purification process involves first extracting with ethyl acetate, then drying with anhydrous Na2SO4, filtering, reducing pressure, and finally purifying by column chromatography to obtain arylsilyl compounds.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the aryl ether, chlorosilane, and Grignard reagent is 1:3-5:4-8; The amount of the organic solvent used is 3 to 5 times the molar amount of the aryl ether; The amount of the iron catalyst used is 5 to 10% of the molar amount of the aryl ether.

4. The preparation method according to claim 1, characterized in that: The reaction time is 24–48 h; thin-layer chromatography is used to monitor the reaction process.

5. The preparation method according to claim 1, characterized in that: The organic solvent is tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, toluene, n-hexane, 1,4-dioxane, 1,2-dichloroethane, or nitromethane.

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