Introduction of Ionic Liquids - shodhganga.inflibnet.ac.inshodhganga.inflibnet.ac.in/bitstream/10603/4500/9/09_chapter 2.pdf2.1 Introduction Ionic liquids are a fascinating class of

62

CHAPTER – 2

Terpenes to Ionic Liquids: Synthesis and

Characterization of Citronellal-Based Chiral Ionic

Liquids

63

2.1 Introduction

Ionic liquids are a fascinating class of compounds with unique

properties, which have recently attracted the attention of a wide

number of researchers. Numerous works have been published in the

last couple of years reporting the possibility to perform several organic

reactions and catalyzed processes in these new media. They represent

a new class of non-molecular, ionic solvents with a tremendous

potential to replace conventional solvents. They are also considered

as greener alternatives to conventional organic solvents in chemical

transformations due to their low vapor pressure and high boiling

points.1 Particularly, their property of reusability and tolerance for

flammability has prompted their use in chromatographic separation2

and extraction techniques.3 There has been a flurry of activity on the

synthesis, properties and applications of several ionic liquids in the

last decade culminating in several publications and reviews.4-9

Ionic liquids have the potential to play a significant role in

asymmetric synthesis possibly due to their difference in

thermodynamic and kinetic behavior, selectivity and process

performance as compared to conventional organic solvents. Although

synthesis, characterization and application of ionic liquids have

gained more popularity, literature available on chiral ionic liquids is

very limited.

64

Terpenes are an important part of the “chiral pool” and can be

used in the synthesis of chiral ionic liquids. However, the literature

available on the use of terpenes as a chiral pool in ionic liquids is

limited. Tosoni et al. have reported one of the first chiral ionic liquids

derived from citronellol, 1,3-dicitronellyl-1H- imidazolium bromide,10

Scheme-2.1.

Scheme: 2.1 Synthesis of Citronellyl bromide.

Chiral citronellol has been converted into the corresponding

citronellyl bromide followed by alkylation with 1-alkylimidazoles to

give chiral ionic liquid, Scheme-2.2.

NNR

NNR

Br

40 0C, 5 days

R = CH3, C4H9, C6H13, C12H25, C14H29, C18H37

Br3

4

2

Scheme: 2.2 Synthesis of CILs derived from (3R)-Citronellol.

Similarly alkylation of citronellyl bromide with pyridine gives

chiral pyridinium ionic liquid, Scheme–2.3.

65

Br

40 °C, 5 daysBr

N N

5

6

2

Scheme: 2.3 Synthesis of chiral pyridinium ionic liquids.

Another interesting C2-symmetric 1,3-dicitronellyl-1H-

imidazolium bromide was produced via deprotonation with

tetrabutylammonium hydroxide and then reacted with 2 equivalents

of the citronellyl bromide, Scheme-2.4.

Br

(2 eq.), RT, 3 days

Br

N

NH

1) Bu4NOH

NNH

72 8

Scheme: 2.4 Synthesis of CIL derived from (3R)-Citronellol.

Wang et al. investigated chiral pinene-based ionic liquids using

(1S)-α pinene.11 The cis amino alcohol obtained from α-pinene was

converted into chiral oxazoline, followed by alkylation with suitable

alkyl halide to furnish the chiral ionic liquid, Scheme-2.5. The

counter ion could be exchanged with different counter ions like PF6-

and BF4-.

66

OHO

KMNO4

Acetone

OHN

OHNH2OH

Ethanol

LAH

Ether

OHNH2

H

CH3

O

Cl

Dichloromethane

Saturated Na2CO3

OH

NH

O H

CH3N

OH

CH3

MeSO2Cl

Et3N

Dichloromethane

N

OH

CH3

C3H7

Br15(m.p.= 162 °C )

C3H7Br

N

OH

CH3

C3H7

PF6

HPF6

16(m.p.= 140 °C)

N

OH

CH3

C3H7

BF417(m.p.= 120 °C)

9 10 11 12

1314

Scheme: 2.5 Synthesis of CILs derived from -pinene.

Both the above mentioned examples used imidazolium,

pyridinium, oxazolium moieties to construct chiral ionic liquids.

Chirality in these ionic liquids can arise from the anion or from

the cation counterpart of the ionic liquids. Ionic liquids with chiral

anion counterparts have been reported in the literature.12a However,

application of the same in Diels-Alder reaction did not result in

enantioselectivity. Modifications to the cation counterpart of room

temperature chiral ionic liquids have been reported with ammonium,

pyridinium, oxazolium, thiazolium and imidazolium moieties.12 The

67

following work gives the detailed uses of terpene chiral pool for the

preparation of chiral ionic liquids through simple chemical

transformations.

Citronellal is an easily accessible, less expensive chiral starting

material with an aldehyde functionality, which can be conveniently

used for the several chemical transformations to design the desired

carbon framework. It is extensively used in the field of organic

synthesis and an important chiral precursor in the synthesis of

several natural products. The major advantage of citronellal as chiral

precursor is its commercial accessibility in both the chiral forms. The

low boiling point of citronellal is expected to provide a useful chiral

carbon chain to the ionic liquid under study with low melting points

or offer liquid state at room temperature, thus enabling them to open

new opportunities in the field of asymmetric synthesis.

The chiral ionic liquids can be envisaged from citronellal 18,

using a reductive amination strategy with dimethylamine or

diethylamine followed by treatment with an alkyl halide to give the

corresponding chiral ionic liquids 19a-e and 20a-e respectively, as

mentioned in the Figure 2.1.

68

CHO

H

CHO

H

a. X = I, R = Meb. X = I, R = Etc. X = Br, R = n-Prd. X = Br, R = i-Pre. X = Br, R = n-Bu

(S)-18 (S)-20a-e

(R)-18 (R)-20a-e

H

NR

H

NR

(S)-19a-e

(R)-19a-e

H

NR

H

NR

X X

X X

Figure: 2.1 Retrosynthesis of Citronellal-based chiral ionic liquids.

69

2.2 Results and Discussion

As mentioned in the retro synthetic analysis Figure-2.1, the

citronellal (S)-18 is treated with dimethylamine in the presence of

Raney-nickel in hydrogen environment to give the corresponding

amine (S)-21 in excellent yields. The dimethylamine 21, thus

obtained, is treated with different alkyl halides for eg., methyl iodide,

ethyl iodide, n-propyl bromide, iso-propyl bromide, n-butyl bromide,

etc., to give the corresponding quaternary ammonium salts (S)-19a-e

in good yields. Although the reaction proceeded smoothly with methyl

and ethyl halides, the reactivity with iso-propyl bromide was observed

to be sluggish with longer reaction time. Similarly, the other

commercially available isomer, (R)-citronellal, was also reacted with

dimethylamine in presence of Raney-nickel and hydrogen to give the

corresponding amine (R)-21, which on further treatment with the

alkyl halides furnished the desired chiral ammonium salts (R)-19a-e

in good yields, Scheme-2.6.

70

CHO

H H

N

H

NR X

CHO

H H

N

H

NR X


(S)-18 (S)-21 (S)-19a-e

(R)-18 (R)-21 (R)-19a-e

a b

ba

a) Dimethylamine, MeOH, Raney-nickel, H2 balloon, RT- overnight.

b) Acetonitrile, R-X, RT- overnight.

Scheme: 2.6 Synthesis of chiral ionic liquids starting from citronellal and dimethylamine as amine source.

The scope of the reaction was extended to diethylamine to

understand the physical properties of the resulting ionic liquids with

citronellal. Thus, citronellal (S)-18 was treated with diethylamine in

the presence of Raney-nickel and hydrogen to give the corresponding

diethylamine (S)-22. The diethylamine derivative (S)-22 was further

treated with different alkyl halides for eg., methyl iodide, ethyl iodide,

n-propyl bromide, iso-propyl bromide, n-butyl bromide, etc., to give

the corresponding quaternary ammonium salts (S)-20a-e in good

yields. Similar observations were experienced in the reaction of iso-

propyl bromide with diethyl substrate, in which the reaction was

observed to be sluggish. Similarly, the chemistry was repeated with

(R)-citronellal and diethylamine in presence of Raney-nickel and

71

hydrogen to give the corresponding amine (R)-22, which on further

treatment with alkyl halides yielded the chiral ammonium salts (R)-

20a-e in good yields, Scheme-2.7. All the chiral ionic liquids prepared

using reductive amination with dimethylamine were found as liquid at

room temperature except (S) and (R)-19a. Similarly, all the new chiral

ionic liquids were prepared using reductive amination with

diethylamine were found to be liquids at room temperature, table-2.1.

CHO

H H

N

CHO

H H

N


(S)-18 (S)-22 (S)-20a-e

(R)-18 (R)-22 (R)-20a-e

H

NR

H

NR

X

X

a

a

b

b

a) Diethylamine, MeOH, Raney-nickel, H2 balloon, RT- overnight

b) Acetonitrile, R-X, RT-overnight.

Scheme: 2.7 Synthesis of chiral ionic liquids starting from citronellal

and diethylamine as amine source.

72

Table: 2.1

Preparation of compounds (S)-19a-e, (R)-19a-e, (S)-20a-e, and (R)-20a-e

Compound

No. R X

SOR

(C= 1, MeOH) M.P.

(S)-19a Me I- 3.09 Yellow Solid

(S)-19b Et I- 2.96 Liquid

(S)-19c n-Pr Br- 3.96 Liquid

(S)-19d Iso-Pr Br- 3.55 Liquid

(S)-19e n-Bu Br- 3.28 Liquid

(R)-19a Me I- -1.26 Yellow Solid

(R)-19b Et I- -1.34 Liquid

(R)-19c n-Pr Br- -2.27 Liquid

(R)-19d Iso-Pr Br- -2.43 Liquid

(R)-19e n-Bu Br- -2.08 Liquid

(S)-20a Me I- 3.32 Liquid

(S)-20b Et I- 2.94 Liquid

(S)-20c n-Pr Br- 4.38 Liquid

(S)-20d Iso-Pr Br- 2.83 Liquid

(S)-20e n-Bu Br- 3.22 Liquid

(R)-20a Me I- -1.52 Liquid

(R)-20b Et I- -2.15 Liquid

(R)-20c n-Pr Br- -3.0 Liquid

(R)-20d Iso-Pr Br- -2.75 Liquid

(R)-20e n-Bu Br- -3.22 Liquid

73

Reductive amination product dimethylamine (21) was confirmed

from the 1H NMR study, absence of aldehyde proton at δ 9.7 ppm and

appearance of a new peak at δ 2.2 (S, 6H) corresponds to

dimethylamine protons, peak at δ 2.2 (t, 2H) corresponds to N-CH2.

The quaternization of 21 with methyl iodide product (19a) was

confirmed from the 1H NMR peak at δ 3.4-3.5 (S, 9H) which

corresponds to trimethylamine (N-(CH3)3), peak at δ 3.5-3.7 (m, 2H)

corresponds to N-CH2 protons as seen from 1H NMR study.

Reductive amination product diethylamine (22) was confirmed

from 1H NMR study. The aldehyde peak at δ 9.7 ppm disappeared in

the product, and appeared of a new peak at δ 2.5-2.6 (q, 4H)

corresponds to the methylene group of N-(CH2)-CH3)2 and a singlet at

δ 1.7 ppm (6H, 2-CH3 of N-(CH2-CH3)2. The other peak of the product

appeared at δ 2.3-2.4 (m, 2H) of N-CH2. The quaternization of 22 was

carried out using methyl iodide, product 20a was confirmed from 1H

NMR study. The peak at δ 3.5-3.6 (m, 4H) corresponded to N-(CH2-

CH3)2, while the peaks at δ 3.3-3.5 (dd, 2H) of N-CH2-CH2 and δ 3.21

(S, 3H) corresponded to N-CH3, confirming the product.

74

2.3 Conclusion

In summary, several new chiral ionic liquids were prepared

starting from both the chiral isomers of citronellal as the chiral

starting material and dialkylamine as the amine source. The Schiff

base thus obtained was reduced and further reacted with alkyl halides

containing different carbon chains. The strategy could be generalized

with other dialkylamines to design a chiral ionic liquid for any specific

use. Most of the ionic liquids isolated were liquids at room

temperature and amenable for the application in asymmetric

synthesis.

75

2.4 Experimental Section

All the chemicals and reagents of LR grade were used. 1H NMR

spectra were recorded on Varian Gemini 2000 model 400 MHz

instrument using TMS as an internal standard in CDCl3 (Chemical

shifts in ppm) and mass spectrum was recorded on HP 5989A

spectrometer. Optical Rotation of the compounds were recorded on

Polari meter (Jasco) in methanol (c=1).

General procedure for synthesis of compounds (21 & 22) :

To a stirred solution of compound (S) or (R)-18 (1.0 mmol), in

methanol (10 vol) was added appropriate alkylamine (1.5 mmol) and

Raney-nickel (30% w/v) at room temperature. Reaction was left to stir

for 20 hrs at room temperature in hydrogen environment, the catalyst

was filtered and the solvent was evaporated under reduced pressure.

The resulting crude (pale greenish liquid) was subjected to column

chromatography to give pure desired products (21& 22).

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (dimethyl) amine

(21) : To a stirred solution of (3S) or (3R)-3,7-dimethyl-6-octenal (18)

(5.0 g, 32.4 mmol) in methanol (50 mL) was added 40% aqueous

solution of dimethylamine (2.4 mL, 48.6 mmol) and Raney-nickel (30%

w/v) at room temperature. Reaction was left to stir for 20 hrs at room

temperature in hydrogen environment. After completion of reaction,

the catalyst was filtered and the solvent was evaporated under

reduced pressure. The resulting crude (pale greenish liquid) was

subjected to column chromatography using a mixture of ethyl acetate

76

and pet ether as an eluent to yield 4.2 g (70%) of the pure desired

product (3S) or (3R) -3,7-dimethyl-6-octenyl (dimethyl) amine (21).

1H NMR (400 MHz, CDCl3) : δ 5.0-5.2 (m, 1H), 2.2-2.3 (t, J=7.8 Hz,

2H), 2.0 (s, 6H), 1.9-2.1 (m, 2H), 1.7 (s, 3H), 1.6 (s, 3H), 1.4-1.6 (m,

1H), 1.2-1.4 (m, 2H), 1.1-1.2 (m, 2H), 0.8-0.9 (d, J=6.4 Hz, 3H); 13C

NMR (200 MHz, CDCl3) : δ 130.51, 124.59, 57.51 , 45.17, 45.17,

37.01, 34.47, 30.78, 25.37, 25.20, 19.35, 17.27.

Mass: m/z = 183

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (diethyl)amine

(22): To a stirred solution of (3S) or (3R)-3,7-dimethyl-6-octenal (18)

(5.0 g, 32.4 mmol) in methanol (50 mL) was added diethylamine (5.0

mL, 48.6 mmol) and Raney nickel (30% w/v) at room temperature.

The reaction was left to stir for 20 hrs at room temperature in

hydrogen environment. After completion of the reaction, the catalyst

was filtered and the solvent was evaporated under reduced pressure.

The resulting crude (pale greenish liquid) was subjected to column

chromatography using a mixture of ethyl acetate and pet ether as an

eluent to yield 5.1 g (75%) of the pure desired product (3S) or (3R)-3,7-

dimethyl-6-octenyl (diethyl) amine (22).

1H NMR (400 MHz, CDCl3) : δ 5.0-5.2 (m, 1H), 2.5-2.6 (q, 4H), 2.3-2.4

(m, 2H), 1.9-2.1 (m, 2H), 1.6-1.7 (s, 6H), 1.4-1.5 (m, 2H), 1.2-1.4 (m,

2H), 1.1-1.2 (m, 1H), 1.0 (t, J=6.8 Hz, 6H), 0.8 (d, J=6.4 Hz, 3H); 13C

NMR (200 MHz, CDCl3) : δ 130.51, 124.59, 50.43, 46.55, 36.98,

33.47, 30.77, 25.34, 25.21, 19.41, 17.24, 11.29.

Mass: m/z = 212

77

General procedure for synthesis of compounds (S) or (R)-19a-e and

20a-e:

To a stirred solution of compound (S) or (R)-3 (1.0 mmol) in

acetonitrile (10 vol), alkyl halide (1.2 mmol) was added at room

temperature. The reaction was allowed to stir for 12 hrs at room

temperature and the solvent was removed under reduced pressure,

followed by drying under high vacuum to afford the desired product.

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (trimethyl)

ammonium iodide (19a) : To a stirred solution of compound (S) or

(R)-21 (2.0 g, 10.9 mmol) in acetonitrile (20 mL), methyl iodide (2.0

mL,13.1 mmol) was added at room temperature. The reaction was

allowed to stir for 12 hrs at room temperature and the solvent was

removed under reduced pressure followed by further drying under

high vacuum to afford 3.2 g (90%) of the desired product as a yellow

solid.

1H NMR (400 MHz, CDCl3) : δ 5.0-5.2 (m, 1H), 3.5-3.7 (m, 2H), 3.4-3.5

(s, 9H), 1.9-2.1 (m, 2H), 1.7-1.8 (m, 1H), 1.6-1.7 (s, 6H), 1.5-1.6 (m,

2H), 1.2-1.4 (m, 2H), 0.9-1.0 (d, J=6.4 Hz, 3H); 13C NMR (200 MHz,

CDCl3) : δ 131.32, 123.56, 65.51, (3C, 53.43), 36.36, 29.91, 29.39,

25.32, 24.85, 18.99, 17.39.

Mass: m/z =198

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (ethyl) dimethyl

ammonium iodide (19b) : To a stirred solution of compound (S) or

(R)-21 (2.0 g, 10.9 mmol) in acetonitrile (20 mL), ethyl iodide (1.1 mL,

13.1 mmol) was added at room temperature. The reaction was

78

allowed to stir for 12 hrs at room temperature, and the solvent was

removed under reduced pressure followed by drying under high

vacuum to afford 3.3 g (90%) of the desired product as a liquid.


(m, 2H), 3.39 (s, 6H), 1.9-2.1 (m, 2H), 1.7-1.8 (m, 1H), 1.6-1.7 (s, 6H),

1.5-1.6 (m, 2H), 1.4 (t, J=7.2 Hz, 3H), 1.2-1.3 (m, 2H), 1.0 (d, J=6.4

Hz, 3H); 13C NMR (200MHz, CDCl3) : δ 131.19, 123.42, 62.11, 59.20,

50.65, 50.65, 36.19, 29.84, 28.83, 25.18, 24.72, 18.87, 17.26, 8.28.

Mass: m/z = 212

Preparation of (3S or 3R)-3,7-Dimethyl-6-octenyl (dimethyl)

propyl ammonium bromide (19c) : To a stirred solution of compound

(S) or (R)-21 (2.0 g, 10.9 mmol) in acetonitrile (20 mL), n-prppyl

bromide (1.2 mL, 13.1 mmol) was added at room temperature. The

reaction was allowed to stir for 12 hrs at room temperature and the

solvent was evaporated under reduced pressure followed by further

drying under high vacuum yielding 2.3 g (70%) of the desired product

as a liquid.

1H NMR (400 MHz, CDCl3) : δ 5.0-5.2 (m, 1H), 3.4-3.6 (m, 4H), 3.4 (s,

6H), 1.9-2.1 (m, 2H), 1.7-1.8 (m, 1H), 1.6-1.7 (s, 6H), 1.6 (m, 2H), 1.5-

1.6 (m, 2H), 1.2-1.4 (m, 2H), 1.1 (t, J=7.2 Hz, 3H), 0.9 (d, J=6.4 Hz,

3H); 13C NMR (200MHz, CDCl3) : δ 131.48, 123.63, 64.87, 62.45,

51.14, 36.45, 30.09, 29.10, 25.39, 24.94, 18.96, 17.42, 16.00, 10.40.

Mass: m/z = 226

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (isopropyl)

dimethyl ammonium bromide (19d) : To a stirred solution of

79

compound (S) or (R)-21 (2.0 g, 10.9 mmol) in acetonitrile (20 mL), iso-

propyl bromide (1.6 mL, 13.1 mmol) was added at room temperature.

The reaction was allowed to stir for 12 hrs at room temperature and

the solvent was removed under reduced pressure. The crude product

was purified by column chromatography to yield 1.3 g (40%) of the

desired product as a liquid.


(m, 2H), 3.3-3.4 (s, 6H), 1.9-2.0 (m, 2H), 1.7-1.8 (m, 1H), 1.6-1.7 (s,

6H), 1.4-1.5 (m, 2H), 1.2-1.4 (m, 2H), 1.0-1.1 (m, 6H), 0.9 (d, J=4.8

Hz, 3H); 13C NMR (200MHz, CDCl3) : δ 131.44, 123.63, 64.16, 61.51,

48.04, 36.42, 29.00, 28.87, 25.37, 24.94, 18.93, 17.41, 16.46.

Mass: m/z = 226

Preparation of butyl [(3S or 3R)-3,7-dimethyl-6-octenyl] dimethyl

ammonium bromide (19e) : To a stirred solution of compound (S) or

(R)-21 (2.0 g, 10.9 mmol) in acetonitrile (20 mL), n-butyl bromide (1.4

mL, 13.1 mmol) was added at room temperature. The reaction was


removed under reduced pressure. The obtained crude was subjected

to column chromatography to yield 2.1 g (60%) of the desired product

as a liquid.

1H NMR (400 MHz, CDCl3) : δ 5.0-5.2 (m, 1H), 3.4-3.6 (m, 4H), 3.38 (s,

6H), 1.9-2.1 (m, 2H), 1.8-1.9 (m, 1H), 1.6-1.7 (s, 6H), 1.4-1.5 (m, 4H),

1.39 (m, 2H), 1.2-1.3 (m, 2H), 1.0 (t, J=7.2 Hz, 3H), 0.9 (d, J=6.4 Hz,

3H); 13C NMR (200MHz, CDCl3) : δ 131.67, 123.68, 63.42, 62.43,

80

51.23, 36.57, 30.19, 29.21, 25.50, 25.05, 24.44, 19.39, 19.10, 17.53,

13.52.

Mass: m/z = 240

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (diethyl) methyl

ammonium iodide (20a) : To a stirred solution of compound (S) or

(R)-22 (2.0 g, 9.5 mmol) in acetonitrile (20 mL), methyl iodide (1.8 mL,

11.4 mmol) was added at room temperature. The reaction was



vacuum to yield 3.0 g (90%) of the desired product as a liquid.


(m, 2H), 3.2 (s, 3H), 1.9-2.1 (m, 2H), 1.7 (m, 2H), 1.6 (s, 6H), 1.4-1.5

(m, 2H), 1.3-1.4 (t, J=7.4 Hz, 6H), 1.2-1.3 (m, 1H), 1.0 (d, J=6.4 Hz,

3H); 13C NMR (200MHz, CDCl3) : δ 130.93, 123.14, 58.73, 56.15,

47.54, 35.89, 29.62, 28.20, 24.93, 24.46, 18.62, 17.00, 7.75.

Mass: m/z = 226

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (triethyl)

ammonium iodide (20b) : To a stirred solution of compound (S) or

(R)-22 (2.0 g, 9.5 mmol) in acetonitrile (20 mL), ethyl iodide (0.9

mL,11.4 mmol) was added at room temperature. The reaction was



vacuum to yield 2.8 g (80%) of the desired product as a liquid.

1H NMR (400 MHz, CDCl3): δ 5.0-5.2 (m, 1H), 3.4-3.5 (q, 6H), 3.1-3.3

(m, 2H), 1.9-2.1 (m, 2H), 1.7-1.8 (m, 2H), 1.6-1.7 (s, 6H), 1.5-1.6 (m,

81

2H), 1.4 (t, J=7.2 Hz, 9H), 1.2-1.3 (m, 1H), 1.0 (d, J=6.0 Hz, 3H); 13C

NMR (200MHz, CDCl3): δ 129.97, 122.45, 54.62, 52.07, 35.05, 28.84,

27.07, 24.19, 23.71, 17.91, 16.26, 6.80.

Mass: m/z = 240

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (diethyl) propyl

ammonium bromide (20c) : To a stirred solution of compound (S) or

(R)-22 (2.0 g, 9.5 mmol) in acetonitrile (20 mL), n-propyl bromide (1.0





as a liquid.


(m, 4H), 1.9-2.1 (m, 2H), 1.8-1.9 (m, 2H), 1.7-1.8 (m, 2H), 1.6-1.7 (s,

6H), 1.5-1.6 (m, 2H), 1.3-1.5 (t, J=7.0 Hz, 6H), 1.2-1.3 (m, 1H), 1.1 (t,

J=7.2 Hz, 3H), 1.0 (d, J=6.8 Hz, 3H); 13C NMR (200MHz, CDCl3) : δ

131.71, 123.59, 59.25, 56.40, 53.86, 36.47, 30.26, 28.47, 25.49,

25.06, 19.14, 17.53, 15.54, 10.71, 7.88.

Mass: m/z = 254

Preparation of (3S or 3R)-3,7-dimethyl-6-octenyl (diethyl)

isopropyl ammonium bromide (20d) : To a stirred solution of

compound (S) or (R)-22 (2.0 g, 9.5 mmol) in acetonitrile (20 mL), iso-

propyl bromide (1.1 mL, 11.4 mmol) was added at room temperature.

The reaction was allowed to stir for 12 hrs at room temperature and

the solvent was removed under reduced pressure. The obtained crude

82

was subjected to column chromatography to yield 0.8 g (25%) of the

desired product as a liquid.

1H NMR (400 MHz, CDCl3) : δ 5.0-5.2 (m, 1H), 3.5 (q, 4H), 3.2-3.3 (m,

2H), 2.6-2.7 (m, 1H), 1.8-2.2 (m, 6H), 1.6-1.7 (s, 6H), 1.4 (t, J=7.2 Hz,

3H), 1.2 (t, J=7.2 Hz, 3H), 1.0 (d, J=6.4 Hz, 3H), 0.9 (d, J=6.4 Hz, 6H).

Mass: m/z = 254

Preparation of Butyl [(3S or 3R)-3,7-dimethyl-6-octenyl] diethyl

ammonium bromide (20e) : To a stirred solution of compound (S) or

(R)-22 (2.0 g, 9.5 mmol) in acetonitrile (20 mL), n-butyl bromide (1.2





as a liquid.


(m, 2H), 3.1 (t, J=7.2 Hz, 2H), 1.9-2.1 (m, 2H), 1.7-1.8 (m, 6H), 1.6-1.7

(s, 6H), 1.5 (m, 2H), 1.3-1.4 (t, J=7.2 Hz, 6H), 1.2-1.3 (m, 1H), 1.1 (t,

J=7.4 Hz, 3H), 0.9 (d, J=6.8 Hz, 3H); 13C NMR (200MHz, CDCl3) : δ

131.50, 123.45, 57.38, 56.18, 53.64, 36.32, 30.09, 28.28, 25.32,

24.89, 23.59, 19.36, 18.99, 17.36, 13.31, 7.71.

Mass: m/z = 268

83

2.5 Spectral data

1H NMR spectrum (400MHz, CDCl3) of compound 18:

1H NMR spectrum (400MHz, CDCl3) of compound 21:

CHO

H

(R)-18

H

N

(R)-21

84

13C NMR spectrum (400MHz, CDCl3) of compound 21:

Mass spectrum of compound 21:

H

N

(R)-21

H

N

(R)-21

85

1H NMR spectrum (400MHz, CDCl3) of compound 19a:

13C NMR spectrum (400MHz, CDCl3) of compound 19a:

86

DEPT spectrum of compound 19a:

Mass spectrum of compound 19a:

87

1H NMR spectrum (400MHz, CDCl3) of compound 19b:

13C NMR spectrum (400MHz, CDCl3) of compound 19b:

88

DEPT spectrum (400MHz, CDCl3) of compound 19b:

Mass spectrum of compound 19b:

89

1H NMR spectrum (400MHz, CDCl3) of compound 19c:

DEPT spectrum (400MHz, CDCl3) of compound 19c:

90

13C NMR spectrum of compound 19c:

Mass spectrum of compound 19c:

91

1H NMR spectrum (400MHz, CDCl3) of compound 19d:

DEPT spectrum of compound 19d:

92

Mass Spectrum of compound 19d:

1H NMR spectrum of compound 19e:

93

DEPT spectrum of compound 19e:

Mass spectrum of compound 19e:

94

13C NMR spectrum of compound 19e:

1H NMR spectrum of compound 22:

95

DEPT spectrum of compound 22:

13C NMR spectrum of compound 22:

96

1H NMR spectrum of compound 20a:

13C NMR spectrum of compound 20a:

97

Mass spectrum of compound 20a:

1H NMR spectrum of compound 20b:

98

DEPT spectrum of compound 20b:

13C NMR spectrum of compound 20b:

99

Mass spectrum of compound 20b:

1H NMR spectrum of compound 20c:

100

DEPT spectrum of compound 20c:

13C NMR spectrum of compound 20c:

H

N

Br

(R)-20c

101

1H NMR spectrum of compound 20d:

Mass spectrum of compound 20d:

102

1H NMR spectrum of compound 20e:

DEPT spectrum of compound 20e:

103

13C NMR spectrum of compound 20e:

Mass spectrum of compound 20e:

104

2.6 References

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Synthesis and Catalysis. Chem. Rev. 1999, 99, 2071-2083; (b)

DuPont, J.; de Souza, R. F.; Suarez, P. A. Z. Ionic Liquid (Molten

Salt) Phase Organometallic Catalysis. Chem. Rev. 2002, 102,

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Perspectives for Organic and Catalytic Reactions. J. Mol. Cat. A:

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Documents

Introduction of Ionic Liquids - shodhganga.inflibnet.ac.inshodhganga.inflibnet.ac.in/bitstream/10603/4500/9/09_chapter 2.pdf2.1 Introduction Ionic liquids are a fascinating class of