LETTER
Nucleophilic Substitution with Recyclable Ionic Liquids
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Table 5 Recyclability of [bmim][X]
MX
[bmim][OTs]
[bmim][X]
OTs
X
n-C6H13
n-C6H13
60 °C, 8 h
8
9
Entry
X
Regeneration of [bmim][X]a
Recycling use of [bmim][X]c and yield (%)
MX
Conv. (%)b
Cycle 1
Cycle 2
Cycle 3
Cycle 4
1
2
3
4
Cl
NaCl/LiCl
KBr/NaBr/LiBr
NaI
0/88
33/90/99
99
90
93
99
97
92
92
95
96
91
92
94
95
91
91
95
95
Br
I
SCN
NaSCN
99
a Reaction conditions: [bmim][OTs] (1.0 mmol), MX (1.0 equiv), MeCN (1.0 mL), 80 °C, overnight.
b The conversions were determined by 1H NMR spectroscopic analysis.
c All reactions were carried out on a 1.0 mmol scale and isolated yields are given.
stitution products by the ILs in excellent yields. In most
cases, the reactions do not require co-solvent systems, ad-
ditional reagents, sophisticated equipment, or special pre-
cautions. The effectiveness of the reactions can be
explained by the two distinctive characteristics of the ILs:
the intrinsic, pronounced nucleophilicity of the anions (X–),
and their polar aprotic nature as the reaction media. These
favorable aspects allow very small amounts of the IL to be
used (1.0 equiv of the reactant) and relatively mild reac-
tion conditions to be applied, providing much greener re-
action protocols than those in reported corresponding
work. Furthermore, under the developed reaction condi-
tions, we found that sulfonate esters derived from second-
ary alcohols also undergo the substitution smoothly,
without much loss of reaction yield or selectivity over the
elimination reactions. The reaction protocols usually re-
sulted in very clean conversions and therefore simple
work-up procedures involving phase separation and con-
centration of the organic layers afforded the desired prod-
ucts with high purity, avoiding expensive and time-
consuming purification steps. We also demonstrated that
the ILs could be regenerated and reused several times
without loss of reactivity, therefore, the ILs can be consid-
ered as catalysts. These aspects of minimum use of re-
agent, simple work-up procedures, and recyclability of the
reagent render the developed protocol a green chemical
process.
References and Notes
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Acknowledgment
This work was supported by the Sungshin Women’s University Un-
Jeong Global Project Research Grant of 2012.
Supporting Information for this article is available online at
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2692–2698