New Journal of Chemistry
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Journal Name
DOI: 10.1039/C5NJ01225B
In reaction mixture, there is existence of organic phase, solid quaternary salt [bmim]Cl (1ꢀbutylꢀ3ꢀmethylimidazolium chloride).
phase and interphase. The substrates and ionic liquid remains in The excess unreacted 1ꢀhaloalkane and toluene were decanted and
organic phase. While the potassium phosphate remains in solid the salt was washed with diethyl ether (3 x 5 ml). The salt was
phase. Phosphate is acting as base, and abstract proton from active further purified by recrystallization from acetonitrile / ethyl acetate
methylene compound. The active methylene compound is to yield the product.
deprotonated in the interphase of organic liquid phase and solid
phase. The organic anion enter into organic phase by exchange
reaction with anion of ionic liquid [bmIm]Cl. It forms an ion
pair (A) of imidazolium cation and organic anion. The anion
reacts with methyl acrylate to give monoꢀMichael addition
product (B). Formation of ion pair is the key step in the reaction.
General procedure for Michael addition: A mixture of 200 mg of
[bmIm]Cl and 100 mg of K3PO4 were stirred at 600C for 2 hours and
then allowed to cool to room temperature. To this mixture , 2mmol
of EAA and 2.2 mmol of methyl acrylate was added and stirred at
room temperature. After completion of reaction (GC), diethyl ether
was added (2X10 ml) and stirred. The separated ether layer was
dried over sodium sulphate and solvent was evaporated to get crude
product. It was further purified by column chromatography.
Owing to steric effects further deprotonation of mono addition
product (B) becomes cumbersome. Also due to bulky nature,
formation of ion pair of imidazolium cation and anion of mono
addition product (B) is difficult. This can be the probable reason of
Procedure for recyclability: After completion of reaction, the
reaction mixture was extracted with diethyl ether (3X30 ml). The
potassium phosphateꢀionic liquid left in the reaction vessel was dried
inder vacuum (3 h). The dried system was used for the next run.
exclusive monoꢀMichael addition reaction.
To support this
mechanism we carried out P31 and DOSY NMR (Figure 1) analysis
of isolated ionic liquid. The probability of metathesis reaction
between potassium phosphate and ionic liquid [bmIm]Cl is
completely warded off due to absence of peak in P31 NMR. Peaks
and diffusion constant values in the DOSY NMR analysis of fresh
and isolated ionic liquid remain unchanged. This clearly depicts that
the ionic liquid do not undergo any structural changes. It remains
intact and work only as facilitator.
Acknowledgment
MMS is thankful to Department of Science & Technology
(DST), New Delhi, and ADS is thankful to Shivaji University,
Kolhapur for the financial support.
Notes and references
aDepartment of Chemistry, Sou. Sushila Danchand Ghodawat Charitable
Trust’s Group of Institutes, Atigre, Kolhapur, Indiaꢀ416118
Eꢀmail: orgadsawant@gmail.com
b Department of Chemistry, Shivaji University, Vidhyanagar, Kolhapur,
Indiaꢀ416004
cYCMOU, Nashik, India.
Fax: (91ꢀ231) 2691533
*Eꢀmail: manikrao.salunkhe@gmail.com
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Figure 1: DOSY NMR analysis of used ionic liquid
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methylene compounds on acrylic esters and acrylonitriles. We have
proposed a mechanism for the reaction based upon some earlier
findings. The mechanism is supported by P31 and DOSY NMR
analysis of ionic liquid. The difficulty of existence of bulky ion pair
of imidazolium cation and anion of mono addition product is a
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Experimental
General procedure for the preparation of [bmIm]Cl: A mixture
of 50 mmol of 1ꢀmethylimidazole and 200 mmol of 1ꢀchlorobutane
in 6 ml dried toluene was refluxed under nitrogen atmosphere for 24
h to obtain a viscous liquid forming the lower layer. The reaction
mixture was cooled to 00C and stirred overnight to yield the solid
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,
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