Synthesis of nitrile functionalized imidazolium-based RTILs

3.3 S YNTHESIS OF RTIL S

3.3.1 Synthesis of nitrile functionalized imidazolium-based RTILs

A new series of propanenitrile imidazolium-based ILs incorporating different sulfonate based anions such as; dioctylsulfosuccinate (DOSS), dodecylsulfate (DDS),

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benzenesulfonate (BS), and trifluoromethanesulfonate (TFMS) were synthesized.

They were prepared by reacting imidazole with acrylonitrile which was then brought to react with 1-haloalkane. After the reaction was completed, metathesis reaction was carried out using (DOSS), (DDS), (BS) and (TFMS) metal anions.

3.3.1.1 Synthesis of 1-alkyl-3-propanenitrile imidazolium bromide

1-alkyl-3-propanenitrile imidazolium bromide ILs were synthesized by following the method shown in Fig 3-1.

N N H

+

^CH2=CHCN

CH₃OH

N N

CH₂CH₂CN

N N

CH₂CH₂CN

+

^{RX N}

N

CH₂CH₂CN R

+

X^-

R = butyl, hexyl ,octyl, decyl X = Br, Cl

50 - 55 ^oC

70 ^oC

Fig 3-1 Synthesis route of the RTILs [C2CN Cnim]X

A 250 mL, round-bottomed flask equipped with a heating oil bath, a nitrogen inlet adapter, magnetic stirrer, reflux condenser is flushed with dry nitrogen. The flask was charged with imidazole (34.04g, 0.5 mol) in methanol (43 mL, 1.0 mol) and mixed with acrylonitrile (39.5 mL, 0.6 mol). The solution was heated under reflux and under nitrogen atmosphere at 50-55 C for 10 hr and then cooled to room temperature. The volatile materials were removed from the mixture under vacuo at 70C. The viscous liquid left was propanenitrile imidazole. Nitrile functionalized IL was synthesized by direct quaternization reaction of the propanenitrile imidazole with 1-bromobutane [182]. 1-brombutane (53.9 ml, 0.5 mol) was added to the propanenitrile. The resulting compound was cooled to room temperature and washed with ethyl acetate for three

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times and the remaining solvent was removed at 80C in vacuo. It was then dried in a vacuum oven for 72 h to produce 1-butyl-3-propanenitrile imidazolium bromide [C2CN Bim]Br.

Similar procedure was repeated to synthesize 1-hexyl-3-propanenitrile imidazolium bromide [C2CN Him]Br, 1-octyl-3-propanenitrile imidazolium bromide [C2CN Oim]Br and 1-decyl-3-propanenitrile imidazolium bromide [C2CN Dim]Br by replacing 1-bromobutane with 1-bromohexane, 1-bromooctane and 1-bromodecane, respectively.

3.3.1.2 Synthesis of 1-alkyl-3-propanenitrile imidazolium chloride

Similar procedure as that described in 3.3.1.1 was adopted to synthesize 1-butyl-3- propanenitrile imidazolium chloride [C2CN Bim]Cl, 1-hexyl-3-propanenitrile imidazolium chloride [C2CN Him]Cl and 1-octyl-3-propanenitrile imidazolium chloride [C2CN Oim]Cl by replacing 1-bromobutane, 1-bromohexane and 1- bromooctane with 1-chlorobutane, 1-chlorohexane and 1-chlorooctane, respectively.

3.3.1.3 Synthesis of 1-alkyl-3-propanenitrile imidazolium dioctylsulfosuccinate

1-alkyl-3-propanenitrile imidazolium dioctylsulfosuccinate [C₂CN C_nim]DOSS ILs were synthesized by following the method shown in Fig 3-2.

1-butyl-3-propanenitrile imidazolium dioctylsulfosuccinate [C₂CN Bim]DOSS was synthesized by mixing 7.74 g, 0.03 mol of [C₂CN Bim]Br and sodium dioctylsulfosuccinate (13.34 g, 0.03 mol) in 50 ml of acetone in a 250-mL round- bottomed flask. The mixture was stirred at room temperature for 48 h. The solid precipitate formed was separated and the solvent removed in vacuo. The resulting pale yellow viscous compound was washed with ethyl acetate and diethyl ether. It was then dried in a vacuum oven for 48 h to give 1-butyl-3-propanenitrile imidazolium dioctylsulfosuccinate [C2CN Bim]DOSS.

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N N

R

N

+

Br^-

R = butyl, hexyl, octyl, decyl

+

⁺

₊

NaBr

O O

S O O

O^-

O O O

O S O O

ONa

O O

N N

R

N Acetone

Fig 3-2 Synthesis route of the RTILs [C2CN Cnim]DOSS

Similar procedure was repeated to synthesize 1-hexyl-3-propanenitrile imidazolium dioctylsulfosuccinate [C2CN Him]DOSS, 1-octyl-3-propanenitrile imidazolium dioctylsulfosuccinate [C2CN Oim]DOSS and 1-decyl-3-propanenitrile imidazolium dioctylsulfosuccinate [C2CN Dim]DOSS by replacing [C2CN Bim]Br with equivalent moles of [C2CN Him]Br, [C2CN Oim]Br and [C2CN Dim]Br, respectively.

3.3.1.4 Synthesis of 1-alkyl-3-propanenitrile imidazolium dodecylsulfate

1-alkyl-3-propanenitrile imidazolium dodecylsulfate [C2CN Cnim]DDS ILs were synthesized by the method shown in Fig 3-3.

N N

R

N

+

Br^-

R = butyl, hexyl, octyl, decyl

+

⁺

+

^NaBr

N N

R

N CH₃(CH₂)₁₀CH₂OSO₃Na

CH₃(CH₂)₁₀CH₂OSO₃^-

Fig 3-3 Synthesis route of the RTILs [C2CN Cnim]DDS

1-butyl-3-propanenitrile imidazolium dodecylsulfate [C2CN Bim]DDS was synthesized by mixing [C2CN Bim]Br (10.33 g, 0.04 mol) and sodium dodecyl sulfate C12H25OSO3Na (11.54 g, 0.04 mol) in 40 ml of hot dionized water (60 °C). The

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mixture was stirred at room temperature for 48 h. The water was slowly removed under vacuo at 80 °C. CH₂Cl₂ was added to the precipitate out the salt and the mixture was filtered. The viscous extract was then washed with deionized water and the washing was repeated until it was bromide-free. The remaining solvent was removed at 80C in vacuo and then dried in a vacuum oven for 48 h to produce the viscous gel product, 1-butyl-3-propanenitrile imidazolium dodecylsulfate [C2CN Bim]DDS.

Similar procedure was repeated to synthesize 1-hexyl-3-propanenitrile imidazolium dodecylsulfate [C2CN Him]DDS, 1-octyl-3-propanenitrile imidazolium dodecylsulfate [C2CN Oim]DDS and 1-decyl-3-propanenitrile imidazolium dodecylsulfate [C2CN Dim]DDS by replacing [C2CN Bim]Br with equivalent moles of [C2CN Him]Br, [C2CN Oim]Br and [C2CN Dim]Br, respectively.

3.3.1.5 Synthesis of 1-alkyl-3-propanenitrile imidazolium sulfobenzoic acid

1-alkyl-3-propanenitrile imidazolium sulfobenzoic acid [C2CN Cnim]SBA ILs were synthesized by following the method shown in Fig 3-4.

N N

R

N

+

Br^-

R = hexyl,octyl, decyl

+ ⁺

^N

+

^NaBr

N R

N SO₃Na

HOOC

SO₃^-

HOOC

Fig 3-4 Synthesis route of the RTILs [C2CN Cnim]SBA

1-hexyl-3-propanenitrile imidazolium sulfobenzoic acid [C2CN Him]SBA, 1- octyl-3-propanenitrile imidazolium sulfobenzoic acid [C2CN Oim]SBA and 1-decyl- 3-propanenitrile imidazolium sulfobenzoic acid [C2CN Him]SBAwere synthesized by following the same procedure as that described in 3.3.1.4 by adding equivalent moles of sodium sulfobenzoic acid HOOCC6H4SO3Na to [C2CN Him]Br, [C2CN Oim]Br and [C2CN Dim]Br, respectively.

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3.3.1.6 Synthesis of 1-alkyl-3-propanenitrile imidazolium benzenesulfonate

1-alkyl-3-propanenitrile imidazolium benzenesulfonate [C₂CN C_nim]BS ILs were synthesized by following the method shown in Fig 3-5.

N N

R

N

+

Br^-

R = butyl, hexyl,octyl

+ ⁺

^N

+

^NaBr

N R

N SO₃Na

SO₃^-

Fig 3-5 Synthesis route of the RTILs [C2CN Cnim]BS

1-butyl-3-propanenitrile imidazolium benzenesulfonate [C₂CN Bim]BS,1-hexyl- 3-propanenitrile imidazolium benzenesulfonate [C₂CN Him]BS and 1-octyl-3- propanenitrile imidazolium benzenesulfonate [C₂CN Oim]BS were synthesized by following the same procedure as that described in 3.3.1.4 by adding equivalent moles of sodium benzenesulfonate C₆H₅SO₃Na to [C₂CN Bim]Br, [C₂CN Him]Br and [C2CN Oim]Br, respectively.

3.3.1.7 Synthesis of 1-alkyl-3-propanenitrile imidazolium trifluoromethanesulfonate

1-butyl-3-propanenitrile imidazolium trifluoromethanesulfonate [C2CN Cnim]TFMS ILs were synthesized by following the method as shown in Fig 3-6.

N N

R

N

+

Br^-

R = butyl, hexyl, octyl

+ ⁺

^N

+

^NaBr

N R

N SO₃Na

F F F

SO₃^- F F F

Fig 3-6 Synthesis route of the RTILs [C₂CN C_nim]TFMS

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1-butyl-3-propanenitrile imidazolium trifluoromethanesulfonate [C₂CN Bim]TFMS,1-hexyl-3-propanenitrile imidazolium trifluoromethanelsulfonatee [C₂CN Him]TFMS and 1-decyl-3-propanenitrile imidazolium trifluoromethanelsulfonate [C2CN Oim]TFMS were synthesized by following the same procedure as that described in 3.3.1.4 by adding equivalent moles of lithium trifluoromethanelsulfonate CF3SO3Li to [C2CN Bim]Br, [C2CN Him]Br and [C2CN Oim]Br, respectively