Table 3 Direct esterification of different carboxylic acids with EtOH
over catalyst 2
increase the Brønsted acid strength as a result of a novel
proposed acid site cooperativity mechanism.
The authors acknowledge IASBS Research Councils and
Iran National Science Foundation (INSF) for support of this
work. We also acknowledge Dr Saeed Emadi from IASBS for
his help and correcting the manuscript.
Entry
Acids
EtOH (mL)
Yielda (%)
1
2
3
4
5
6
7
8
9
Benzoic acid
Benzoic acid
4-Nitrobenzoic acid
3-Methoxybenzoic acid
3-Phenylpropionic acid
Capric acid
Lauric acid
Palmitic acid
Stearic acid
0.7
0.7
0.7
0.7
0.7
1.0
1.2
1.5
1.5
Traceb
94
95
94
96
91
91
88
87
Notes and references
1 (a) J. Otera, Esterification: Methods, Reactions and Applications,
Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim, 1st edn, 2003.
2 (a) Y. Leng, J. Wang, D. Zhu, X. Ren, H. Ge and L. Shen, Angew.
Chem., Int. Ed., 2008, 48, 168; (b) K. Ishihara, S. Ohara and
H. Yamamoto, Science, 2000, 290, 1140; (c) K. Manabe, X. Sun
and S. Kobayashi, J. Am. Chem. Soc., 2001, 123, 10101;
(d) L. Gang, L. Xinzong and W. Eli, New J. Chem., 2007,
31, 348; (e) G. Bartoli, J. Boeglin, M. Bosco, M. Locatelli,
M. Massaccesi, P. Melchiorre and L. Sambri, Adv. Synth. Catal.,
2005, 347, 33; (f) A. G. M. Barret and D. C. Braddock, Chem.
Commun., 1997, 351; (g) K. Manabe and S. Kobayashi, Adv. Synth.
Catal., 2002, 344, 270; (h) H. Firouzabadi, N. Iranpoor and
S. Farahi, J. Mol. Catal. A: Chem., 2008, 289, 61; (i) T. Ooi,
H. Sugimoto, K. Doda and K. Maruoka, Tetrahedron Lett., 2001,
42, 9245; (j) W.-J. Yoo and C.-J. Li, Tetrahedron Lett., 2007,
48, 1033; (k) Y. Nakatami, Y. Koizumi, R. Yamasaki and S. Saito,
Org. Lett., 2008, 10, 2067; (l) K. Wakasugi, A. Nakamura and
Y. Tanabe, Tetrahedron Lett., 2001, 42, 7427.
3 (a) T. Kawabata, T. Mizugaki, K. Ebitami and K. Kaneda,
Tetrahedron Lett., 2003, 44, 9205; (b) K. V. N. S. Srinivas,
I. Mahender and B. Das, Synthesis, 2003, 2479.
4 (a) I. K. Mbaraka, D. R. Radu, V. S.-Y. Lin and B. H. Shanks,
J. Catal., 2003, 21, 329; (b) N. Gokulakrishnan, A. Pandurangan
and P. K. Sinha, J. Mol. Catal. A: Chem., 2007, 263, 55;
(c) J. A. Melero, L. F. Bautista, G. Morales, J. Iglesias and
R. Sanchez-Vazquez, Chem. Eng. J., 2010, 161, 323; (d) Q. Yang,
M. P. Kapoor, S. Inagaki, N. Shirokura, J. N. Kondo and
K. Domen, J. Mol. Catal. A: Chem., 2005, 230, 85.
5 (a) I. K. Mbaraka and B. H. Shanks, J. Catal., 2005, 229, 365;
(b) I. K. Mbaraka and B. H. Shanks, J. Catal., 2006, 244, 78;
(c) L. Sherry and J. A. Sullivan, Catal. Today, 2011, 175, 471.
6 (a) B. Karimi and D. Zareyee, Org. Lett., 2008, 10, 3989; (b) A. Corma
and M. Renz, Angew. Chem., Int. Ed., 2007, 46, 298; (c) C. Tsai,
H. Chen, S. M. Althaus, K. Mao, T. Kobayashi, M. Pruski and
V. S.-Y Lin, ACS Catal., 2011, 1, 729; (d) Q. Yang, S. Ma, J. Li,
F. Xiao and H. Xiong, Chem. Commun., 2006, 2495; (e) K. Inumaru,
T. Ishihara, Y. Kamiya, T. Okuhara and S. Yamanaka, Angew. Chem.,
Int. Ed., 2007, 46, 7625.
7 (a) Y. Gu, C. Ogawa, J. Kobayashi, Y. Mori and S. Kobayashi,
Angew. Chem., Int. Ed., 2006, 118, 7375; (b) Y. Gu, A. Karam,
F. Jeromi and J. Barrault, Org. Lett., 2007, 9, 3145; (c) A. Riisager,
K. M. Eriksen, P. Wasserscheid and R. Fehrmann, Catal. Lett.,
2003, 90, 149; (d) A. Riisager, P. Wasserscheid, R. van Hal and
R. Fehrmann, J. Catal., 2003, 219, 252; (e) F. Shi, Q. Zhang, D. Li
and Y. Deng, Chem.–Eur. J., 2005, 11, 5279.
a
Yields refer to isolated pure products with 10 mol% of catalyst 2 at
b
room temperature and 40 h, unless otherwise stated. Reaction
carried out at room temperature for 40 h with no catalyst.
excellent isolated yields (Table 3, entries 3–9). In all cases, the
experimental set-up was remarkably simple, requiring neither
dry glassware nor inert atmosphere.
As summarized in Table 1, catalyst 2 showed significantly
higher performance than either un-modified SBA-15-Pr–SO3H
1 or homogeneous ionic liquid [MOIm]HSO4 in our ester
production protocols. At this stage, we do not have a precise
explanation for these remarkable catalytic differences. However,
the results in Table 1 imply that the esterification reaction in
our protocol was neither caused by leached [MOIm]HSO4 nor
functionalized SBA-15-Pr–SO3H 1 alone, and our catalyst
system is likely operated in a cooperative pathway.
Therefore, the confinement of [MOIm]HSO4 in close proximity
of anchored sulfonic acid moieties inside the mesochannels of 2
might indeed increase the Brønsted acid strength as a result of the
proposed acid site cooperativity (Fig. 1).5a It is also not surprising
to speculate that the loaded ionic liquid bearing N-octyl group
could also provide enough hydrophobicity for a fast mass transfer
of starting material over the catalyst and expel out the water which
is formed during the reaction from the catalyst surface (Fig. 1).
In conclusion, we have introduced a highly powerful and
water-tolerant Brønsted solid acid catalyst that shows remark-
able and somewhat extraordinary catalytic activity in direct
esterification of alcohols and carboxylic acids at room tempera-
ture under solvent-free conditions. The catalyst comprises of a
hydrophobic task-specific ionic liquid [OMIm][HSO4] charged
in close proximity of anchored sulfonic acid groups in the
interior of nanospaces of ordered mesoporous silica SBA-15.
It is believed that while the hydrophobic nature of the ionic
liquid afforded paths for efficient mass transfer of starting
materials to the active sites, at the same time, it might also
8 (a) A. E. Visser, R. P. Swatloski, W. M. Reichert, R. Mayton,
S. Sheff, A. Wierzbicki, J. H. Davis Jr. and R. D. Rogers, Chem.
Commun., 2001, 135; (b) D. M. Chisholm and J. S. McIndoe, Dalton
Trans., 2008, 3933; (c) Z. Yacob, J. Shah, J. Leistner and J. Liebscher,
Synlett, 2008, 2342; (d) A. E. Visser, R. P. Swatloski, W. M. Reichert,
R. Mayton, S. Sheff, A. Wierzbicki, J. H. Davis Jr. and R. D. Rogers,
Chem. Commun., 2001, 135; (e) S. Luo, X. Mi, L. Zhang, S. Liu,
H. Xu and J. Cheng, Angew. Chem., Int. Ed., 2006, 45, 3093.
9 B. Karimi and E. Badreh, Org. Biomol. Chem., 2011, 9, 4194.
10 See ESIw for experimental details.
11 D. Margolese, J. A. Melero, S. C. Christiansen, B. F. Chmelka and
G. D. Stucky, Chem. Mater., 2000, 12, 2448.
12 The appropriate amount of [MOIm]HSO4 to fill nanospaces of
SBA-15-Pr–SO3H catalyst 1 was optimized by comparing the
performance of the resulting IL@SBA-15-Pr–SO3H bearing
different amounts of ionic liquid in typical esterification reaction
of 1-octanol with acetic acid at room temperature for 40 h.
13 The proton equivalent was correlated using pH analysis of a
weighted sample of the employed catalyst system in Table 1 after
ion exchange with a 1 M solution of NaCl.
Fig. 1 A possible cooperative mechanism which accounts the high
catalytic activity of 2 in the described esterification protocols.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 3327–3329 3329