Chapter 8
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Unprecedented Synthesis of 1,3-dialkylimidazolium2-carboxylate Applications in the Synthesis of Halogen-Free Ionic Liquids and Reactivity as Carbon Dioxide Transfer Agent to Active C-H Bonds 1,2
3
1,2,
M . Aresta , I. Tkatchenko , and I. Tommasi * 1
Department of Chemistry, University of Bari, Campus Universitario, via Orabona 4, 70126 Bari, Italy METEA Research Center, University of Bari, 70126 Bari, Italy Laboratoire de Synthèse et Electrosynthèse Organométallique, UMR 5632 CNRS, University of Burgundy, 9 ave A. Savary, BP 47870, 21078 Dijon, France 2
3
The paper reports the innovative synthesis of 1,3dialkylimidazolium-2-carboxylates from 1-alkyl imidazoles and dimethylcarbonate. The use of carboxylates in the synthesis of "halogen free" ionic liquids and as CO -transfer agents to organic substrates is also described. 2
Introduction Ionic liquids (ILs) have received a great deal of attention in the last few years because of their large utilization in catalysis (1-4). The availability of "high purity" ILs (i.e. ILsfreefromwater or Cl", Br", Fanions, essentially) is an important issue as impurities may cause significant inactivation of the catalytic species.
© 2003 American Chemical Society In Ionic Liquids as Green Solvents; Rogers, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.
93
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94 The use of organic carbonates as alkylating agents for organic synthesis has attracted the attention of the scientific community (5, 6). Moreover several patents have claimed their use for the preparation of N-onium compounds starting from amines and heterocycles (7-9). We have investigated the alkylation reaction of 1-methyl imidazole with dimethyl caibonate and have isolated the unprecedented 1,3-dimethylimidazolium-2-carboxylate (10, 11). In addition to their preparation, we report here the synthesis of high purity ILs which can be obtained in high yield by decarboxylation of 1,3dialkylimidazolium-2~caiboxylates in the presence of strong acids as proton sources. We also report that the decarboxylation reaction carried out in the presence of a catalyst can be conveniently used for transferring the C 0 moiety to an organic substrate containing an activated C-H bond, affording the relevant carboxylated product. 2
Synthesis of l,3-diaIkyIimidazolium-2-carboxylates The alkylation of 1-methylimidazole with dimethyl carbonate as alkylating agent afforded, with 89 % selectivity, the l,3-dimethylimidazoliuni--2carboxylate species. The other product formed is l,3-dimethylimidazolium-4-carboxylate with 11 % selectivity. Best yield (76 %) was obtained carrying out the reaction in an autoclave at 135 °C for 7 h in methanol as solvent. As already mentioned, the use of dimethyl carbonate as alkylating agent of imidazole and imidazoline derivatives has been reported in two recent patents by Mitsubishi (7) and BASF (9). The Mitsubishi patent (7) describes the methylation of 1,2-dialky limidazoline affording the methylmonocarbonate of 1ethyl, 2,3-dimethylinûdazolinium a ionic liquid (Eq.l).
/
+/
Λ C CHjO
\
Ο
II
— • OCH
s
CH^
oca
(1)
By reaction of this salt with an organic acid, the corresponding 1-ethyl 2,3 dimethylimidazolinium salt of the organic acid is obtained (Eq. 2).
In Ionic Liquids as Green Solvents; Rogers, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.
95 +/~Λ
CH -N 3
||
Ν CHj-CHj
c
. /
Downloaded by COLUMBIA UNIV on July 18, 2012 | http://pubs.acs.org Publication Date: August 26, 2003 | doi: 10.1021/bk-2003-0856.ch008
