6406 Wei et al.
Asian J. Chem.
The effects of the ratio of ionic liquid and protic acid to
ACKNOWLEDGEMENTS
ester on this transformation were also explored. In the 2 h
reaction, conversion increased from 40 to 96 % when the ratio
was increased from 1 to 3 (Table-1, Entries 1, 10 and 11). Increase
of the ratio to 4 has no significant effect on the conversion of
benzoic acid (Table-1, Entry 12). However, prolonging the
reaction time was found to significantly increase the conversion
of methyl benzoate (Table-1, Entries 13 and 14).
The authors are grateful to the Foundation of Hubei Educa-
tional Commission (No.B20111702) for financial support.
REFERENCES
1. E.M. Keramane, B. Boyer and J.P. Roque, Tetrahedron Lett., 42, 855 (2001).
2. D.A. Evans, D.H.B. Halstead and D.P. Campos, J. Am. Soc. Chem., 121,
6816 (1999).
We also investigated the effects of different reaction
temperature and time on this conversion. The yield increased
from 65 to 96 % for a 2 h reaction period when the reaction
temperature increased from 80 to 120 ºC (Table-1, Entries 1
and 15). Increase of the reaction temperature to 140 ºC has a
marginal effect on the yield of benzoic acid (Table-1, Entry
16). The yield increased from 72 to 96 % with prolonging the
reaction time from 1 to 2 h (Table-1, Entries 1 and 17) and
extending the reaction time to 3 h has no practically effect on
the yield indicating that the reaction is complete in 2 h (Table-
1, Entry 18).
3. A. Loupy, M. Pedoussaut and J. Sansoulet, J. Org. Chem., 51, 740 (1986).
4. G. Blay, M.L. Cardona, M.B. Garcia and J.R. Pedro, Synthesis, 438
(1989).
5. Y.Q. Wu, D.C. Limburg, D.E. Wilkinson, M.J. Vaal and G.S. Hamilton,
Tetrahedron Lett., 41, 2847 (2000).
6. R. Kaul, Y. Brouillette, Z. Sajjadi, K.A. Hansford and W.D. Lubell, J.
Org. Chem., 69, 6131 (2004).
7. P. Wasserscheid and W. Keim, Angew. Chem. Int. Ed., 39, 3772 (2000).
8. J.S. Wilkes, J. Mol. Catal. A, 214, 11 (2003).
9. V.I. Parvulescu and C. Hardacre, Chem. Rev., 107, 2615 (2007).
10. S. Zhou, L. Liu, B. Wang, F. Xu and R. Su, Asian J. Chem., 25, 240 (2013).
11. X. Sun, H. Luo and S. Dai, Chem. Rev., 112, 2100 (2012).
12. H. Sheikhloie, M.S. Tehrani and S.W. Husain, Asian J. Chem., 25, 1831
(2013).
To enlarge the scope of the deprotection method,
deprotection of various esters has been performed using ionic
liquid 1 in the presence of methane sulfonic acid, the results
are shown in Table-2. Interestingly, this deprotection method
is compatible with many functional groups. Clearly, the
presence of alkyl, hydroxyl, nitro and bromine functions does
not disturb ester cleavage (Table-2, Entries 1-6). Furthermore,
the same conditions are effective for the deprotection of
aliphatic esters (Table-2, Entry 7).
13. D. Ingildeev, F. Hermanutz, K. Bredereck and F. Effenberger, Macromol.
Mater. Eng., 297, 585 (2012).
14. Z. Jiao and X. Fang, Asian J. Chem., 25, 2143 (2013).
15. H. Ohno, "ElectrochemicalAspects of Ionic Liquids", Wiley, NewYork
(2005).
16. Q. Ren, S. Dong, J. Wu, F. Li and J. Miao, Asian J. Chem., 24, 5377 (2012).
17. M.D. Joshi and J.L. Anderson, RSC Adv., 2, 5470 (2012).
18. L. Wang, H. Zhu, C. Ma and Y. Yan, Asian J. Chem., 25, 2129 (2013).
19. S. Boovanahalli, D.W. Kim and D. Chi, J. Org. Chem., 69, 3340 (2004).
20. R. Sheldon, Chem. Commun., 2399 (2001).
21. N. Gupta, G.L. Kad and J. Singh, Catal. Commun., 8, 1323 (2007).
22. A.R. Hajipour, M. Mostafavi and A.E. Ruoho, Monatsh. Chem., 138,
569 (2007).
In case of such higher esters as ethyl benzoate, the
conversion needs longer reaction time because of the steric
hindrance of alkyl moieties. (Table-2, Entry 8). In the case of
the compound, which possesses two different esters in the
molecule, the selective deprotection was achieved under the
conditions (Table-2, Entry 9).
23. B.M. Wei, Z.Y. Zhang, Z.Q. Dai and K.C. Zhang, Monatsh. Chem., 142,
1029 (2011).
24. E. Janus, L. Goc-Maciejewska, M. Lozynski and J. Pernak, Tetrahedron
Lett., 47, 4079 (2006).
25. H. Guo, J.L. Wang, X. Li, D.S. Lv and X.F. Lin, Chin. J. Catal., 32, 162
(2011).
Conclusion
26. B.J. Cox, S. Jia, Z.C. Zhang and J.G. Ekerdt, Polym. Degrad. Stab., 96,
426 (2011).
In conclusion, we have developed a new and efficient
approach for deprotection of esters using ionic liquid as
nucleophile in the presence of protic acid. This strategy features
good functional group tolerance, excellent yields and easy
workup.
27. J. Buckingham, Dictionary of Organic Compounds, Routledge, NewYork
(1982).
28. N.L. Lancaster, T. Weltib and G.B. Yong, J. Chem. Soc., Perkin Trans. II,
2267 (2001).