Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts

Article abstract of DOI:10.1021/ol026189w

(Matrix presented) Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation.

Full text of DOI:10.1021/ol026189w

ORGANIC
LETTERS
2
002
Vol. 4, No. 15
561-2563
Cyclic Carbonate Formation from
Carbon Dioxide and Oxiranes in
Tetrabutylammonium Halides as
Solvents and Catalysts
2
Vincenzo Cal o´ ,* Angelo Nacci, Antonio Monopoli, and Antonello Fanizzi
Department of Chemistry, Istituto di Chimica dei Composti Organometallici
(Sezione di Bari), Via Amendola 173, UniVersity of Bari, 70126-Bari, Italy
calo@chimica.uniba.it
Received May 15, 2002
ABSTRACT
Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric
pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation.
6
-8
9
The chemical fixation of CO
as epoxides, which affords cyclic carbonates, is an important
process (Scheme 1), as it allows the transformation of
2
onto organic compounds such
metal complexes,
magnesium oxide, calcinated hydro-
1
0
talcites, and phthalocyaninatoaluminum in supercritical
carbon dioxide are known to catalyze activation of the CO
11
2
molecule. More recently, propylene carbonate was synthe-
sized in imidazolium tetrafluoroborate as solvent under
1
2,13
electrochemical conditions.
temperatures, high pressures of CO
such as DMF or CH Cl have been thought to be necessary.
For these processes, high
Scheme 1
2
, and toxic polar solvents
2
2
However, under these reaction conditions, some inactive or
polymerization-sensitive oxiranes can be hardly converted
to the corresponding cyclic carbonates.
We report a straightforward method for chemical fixation
2
of CO onto epoxides by simply dissolving these compounds
harmful waste such as CO
engineering plastics, cosmetics, and polar solvents.
Many inorganic and organic compounds including amines,
2
into useful raw materials for
1
,2
3
(6) Kruper, W. J.; Dellar, D. V. J. Org. Chem. 1995, 60, 725-727.
7) Magdesieva, T. V.; Milovanov, S. V.; Lokshin, B. V.; Klemenkova,
Z. S.; Tomilova, L. G. Russ. Chem. Bull. 1998, 47, 2137-2145.
8) Kim, H. S.; Kim, J. J.; Lee, B. G.; Jung, O. S.; Jang, H. G.; Kang,
(
3
4
5
phosphanes, organotin halides, alkali metal salts, transition
(
S. O. Angew. Chem., Int. Ed. 2000, 39, 4096-4098.
(9) Yano, T.; Matsui, H.; Koike, T.; Ishiguro, H.; Fujihara, H.; Yoshihara,
M.; Maeshima, T. Chem. Commun. 1997, 1129-1130.
(10) Yamaguchi, K.; Ebitani, K.; Yoshida, T.; Yoshida, H.; Kaneda, K.
J. Am. Chem. Soc. 1999, 121, 4526-4527.
(
1) Behr, A. Carbon Dioxide ActiVation by Metal Complexes; VCH: New
York, 1988.
(
2) Darensbourg, D. J.; Holtcamp, M. W. Coord. Chem. ReV. 1996, 153,
1
55-174.
(
3) Brind o¨ pke, G. German Pat. DE 3529263, 1987.
4) Baba, A.; Nozaki, T.; Matsuda, H. Bull. Chem. Soc. Jpn. 1987, 60,
(11) Lu, X. B.; Pan, Y. Z.; Ji, D. F.; He, R. Chin. Chem. Lett. 2000, 11,
589.
(
1
552-1554.
(12) Deng, Y.; Peng, J. New J. Chem., 2001, 25, 639.
(13) Yang, H.; Gu, Y.; Deng, Y.; Shi, F. Chem. Commun. 2002, 274.
(
5) Kihara, N.; Hara, N.; Endo, T. J. Org. Chem. 1993, 58, 6198-6202.
1
0.1021/ol026189w CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/29/2002

Table 1. Synthesis of Cyclic Carbonates in
Scheme 2
Tetralkylammonium Salts
1
6
solvents due to low solvation. If so, the substitution in the
ammonium salt of a bromide ion by a more nucleophilic
iodide ion would yield better results such as an increase of
1
7-20
reaction rate.
Indeed, by using a mixture of TBAB and
tetrabutylammonium iodide (TBAI), the conversion rate
increased as glycidyl methacrylate reacted fully in only 1 h
(
Table 1, run 2, method A). As a clean chemical process
should require the lowest possible energy input and solvent
quantity, we tested the CO fixation method by dissolving
2
only 10% (w/w) of TBAI into liquid epoxides at 60 °C.
Though the rates were lower, all of the epoxides reacted well
to afford pure carbonates (method B).
In addition to the anion effect, we tested a possible role
exerted by the cation on this reaction. This was explored by
using the salts 1 and 2 and the poly(N-methyl-4-vinylpyri-
dinium) salt 3 as catalysts (10% w/w), which were found
inefficient at 60 °C (Figure 1). Furthermore 1 and 3
decomposed by increasing the temperature (Table 1, entries
a
Isolated yields are average of at least two runs; >95% pure as judged
by H NMR and GC. As method A but with TBAB as solvent. c Catalyst
1
b
d
e
1
. Catalyst 2. Catalyst 3.
1
4-16).
in molten tetrabutylammonium bromide (TBAB) as solvent,
in the presence of CO at atmospheric pressure. Once the
2
reaction was complete, pure cyclic carbonates were isolated
by vacuum distillation or extraction with ethyl acetate, in
which the ionic liquid is insoluble. This procedure allowed
the recycling of the ammonium salt.14 Polymerization-
sensitive epoxides also reacted very well. For example, the
glycidyl methacrylate was converted into the corresponding
carbonate in 4 h without polymerization (Table 1, run 1).
A plausible mechanism for this reaction is the ring opening
of the epoxide by means of a nucleophilic attack by the
bromide ion, which leads to an oxy anion species affording
Figure 1.
the corresponding cyclic carbonate after reaction with CO
Scheme 2).
This is conceivable15 since the anions may have greatly
enhanced nucleophilicity in the absence of other organic
2
We believe that the better performance of tetralkylammo-
nium salts as catalysts could be ascribed to the structural
differences among [NBu ] and [bmim] (1-butyl-3-meth-
4
(
+
+
(
14) General Procedure. Method A: 20 g of epoxide and 50 g of a
(16) Reichardt, C. SolVents and SolVent Effects in Organic Chemistry,
2nd ed.; VCH: New York, 1988.
mixture of TBAB and TBAI (1:1 w/w) were added to a Schlenk flask,
stirred, and heated at 120 °C under CO2. The reaction pressure (1 bar CO2)
was held constant by means of a CO2 reservoir connected to the flask. After
the proper reaction time, the flask was cooled and the carbonate was distilled
under reduced pressure or extracted with ethyl acetate, leaving the
ammonium salts, which were further recycled. Method B: 3 g of TBAI
dissolved in 30 g of epoxide were heated at 60 °C under CO2 as described
above. The carbonate was distilled or extracted with ethyl acetate.
(17) Cal o´ , V.; Nacci, A.; Lopez, L.; Mannarini, N. Tetrahedron Lett.
2000, 41, 8973-8976.
(18) Cal o´ , V.; Nacci, A.; Lopez, L.; Napola, A. Tetrahedron Lett. 2001,
42, 4701-4703.
(19) Cal o´ , V.; Nacci, A.;. Monopoli, A.; Lopez, L.; di Cosmo, A.
Tetrahedron 2001, 57, 6071-6077.
(20) Cal o´ , V.; Nacci, A. Z. Naturforsch. 2001, 56a, 702-706.
(21) Gannon, T. J.; Law, G.; Watson, P. R.; Carmichael, A. J.; Seddon,
K. R. Langmuir 1999, 15, 8429-8434.
(
15) As a proof for this mechanism, we isolated, in some cases, a small
quantity of bromohydrines.
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Org. Lett., Vol. 4, No. 15, 2002

ylimidazolium) or pyridinium cations, which could influence
the behavior of anions. Indeed, the bulkiness of the tetra-
hedral ammonium ion forces the bromide or iodide ion away
from the cation, and this less electrostatic interaction would
render these anions more nucleophilic. On the contrary, the
Acknowledgment. This work has been supported, in part,
by Ministero dell’Universit a` e della Ricerca Scientifica e
Tecnologica, Rome, and the University of Bari (National
Project: “Stereoselezione in Sintesi Organica: Metodologie
ed Applicazioni”).
2
1
planar cations 1-3, by binding the anion tightly, would
decrease its availability for reaction with epoxides.
OL026189W
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