The Journal of Organic Chemistry
Article
scale. A two-step procedure was performed. First, the molar extinction
coefficient (ε) of the anchor anion was detemined by titrating a
solution of the anchor compound with a solution of a base (1-
methylimidazole) at 480 nm. Then, several aliquots of the anchor
compound were added into a pure ionic liquid, and the absorbance of
the anchor anion was recorded at the same wavelength. The
equilibrium concentrations of the parent anchor and its anion can
then be calculated from the absorbance and ε which then yields the
pKa value. Each pKa thus derived is the average of the data from six to
eight titrations within one run, and the acidity data appeared in Table
1 are the average values of two to three independent runs
(reproducible to ≤0.05 pK unit).
Soc. 1967, 89, 1447. (d) Izutsu, K., Eds. Acid−Base Dissociation
Constants in Dipolar Aprotic Solvents: Blackwell Scientific Publications:
Oxford, 1990. (e) Kutt, A.; Rodima, T.; Saame, J.; Raamat, E.;
̈
Maemets, V.; Kaljurand, I.; Koppel, I. A.; Garlyauskayte, R. Y.;
̈
Yagupolskii, Y. L.; Yagupolskii, L. M.; Bernhardt, E.; Willner, H.; Leito,
I. J. Org. Chem. 2011, 76, 391.
(8) (a) Thomazeau, C.; Olivier-Bourbigou, H.; Magna, L.; Luts, S.;
Gilbert, B. J. Am. Chem. Soc. 2003, 125, 5264. (b) Malham, I. B.;
Letellier, P.; Turmine, M. Talanta 2008, 77, 48. (c) Angelini, G.;
Maria, P. D.; Chiappe, C.; Fontana, A.; Pierini, M.; Siani, G. J. Org.
Chem. 2010, 75, 3912. (d) D’Anna, F.; Marullo, S.; Vitale, P.; Noto, R.
J. Org. Chem. 2010, 75, 4828. (e) Barhdadi, R.; Troupel, M.;
Comminges, C.; Laurent, M.; Doherty, A. P. J. Phys. Chem. B 2012,
116, 277. (f) Johnson, K.; Pagni, R. M.; Bartmess, J. E. Monatsh. Chem.
2007, 138 (11), 1077.
(9) For representative examples, see: (a) Welton, T. Chem. Rev.
1999, 99, 2071. (b) Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed.
2000, 39, 3772. (c) Wasserscheid, P., Welton, T., Eds. Ionic Liquids in
Synthesis; Wiley-VCH: Weinheim, 2008.
ASSOCIATED CONTENT
■
S
* Supporting Information
Table S1, Figures S1−S16, and copies of H NMR and 13C
1
NMR spectra. This material is available free of charge via the
(10) For examples, see: (a) Rogers, R. D.; Seddon, K. R. Science
2003, 302, 792. (b) Rantwijk, F. v.; Sheldon, R. A. Chem. Rev. 2007,
107, 2757. (c) Pinkert, A.; Marsh, K. N.; Pang, S.; Staiger, M. P. Chem.
Rev. 2009, 109, 6712. (d) Armand, M.; Endres, F.; MacFarlane, D. R.;
Ohno, H.; Scrosati, B. Nat. Mater. 2009, 8, 621. (e) Rosen, B. A.;
Salehi-Khojin, A.; Thorson, M. R.; Zhu, W.; Whipple, D. T.; Kenis, P.
J. A.; Masel, R. I. Science 2011, 334, 643.
(11) For examples, see: (a) Cheng, J.-P.; Xian, M.; Wang, K.; Zhu, X.
Q.; Yin, Z.; Wang, P. G. J. Am. Chem. Soc. 1998, 120, 10266.
(b) Cheng, J.-P.; Liu, B.; Zhao, Y.; Wen, Z.; Sun, Y. J. Am. Chem. Soc.
2000, 122, 9987. (c) Cheng, J.-P.; Lu, Y.; Zhu, X. Q.; Sun, Y.; Bi, F.;
He, J. J. Org. Chem. 2000, 65, 3853. (d) Zhu, X. Q.; Li, Q.; Hao, W. F.;
Cheng, J.-P. J. Am. Chem. Soc. 2002, 124, 9887. (e) Zhu, X. Q.; Li, H.-
R.; Li, Q.; Ai, T.; Lu, J.-Y.; Yang, Y.; Cheng, J.-P. Chem.Eur. J. 2003,
9, 871. (f) Chu, Y.; Deng, H.; Cheng, J.-P. J. Org. Chem. 2007, 72,
7790. (g) Zhu, X. Q.; Zhang, M. T.; Yu, A.; Wang, C. H.; Cheng, J.-P.
J. Am. Chem. Soc. 2008, 130, 2501. (h) Li, X.; Deng, H.; Zhang, B.; Li,
J. Y.; Zhang, L.; Luo, S. Z.; Cheng, J.-P. Chem.Eur. J. 2010, 16, 450.
(12) Zhao, W.; Leroy, F.; Heggen, B.; Zahn, S.; Kirchner, B.;
AUTHOR INFORMATION
Corresponding Author
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are sincerely grateful to the Natural Science Foundation of
China (Grant Nos. 20832004, 20902091, 21172112, and
21172118), the National Basic Research Program of China
(973 Program, No. 2010CB833300 and 2012CB821600), and
the State Key Laboratory on Elemento-organic Chemistry for
financial support. J.P.C. wants to thank Prof. Xiao-qing Zhu for
helpful discussions. J.P.C. dedicates this work to his M.Sc.
mentor, the late Prof. Chen-heng Kao, and to his Ph.D. mentor,
the late Prof. Fred Bordwell, for his profound education.
REFERENCES
Balasubramanian, S.; Muller-Plathe, F. J. Am. Chem. Soc. 2009, 131,
̈
■
(1) (a) King, E. J. Acid−Base Equilibria; Pergamon Press: New York,
1965. (b) Bell, R. P. The Proton in Chemistry, 2nd ed.; Cornell
University Press: Ithaca, 1973.
(2) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110,
624.
(3) For representative examples, see: (a) Breslow, R.; Chu, W. J. Am.
Chem. Soc. 1973, 95, 411. (b) Brauman, J. I. In Frontiers of Free Radical
Chemistry; Pryor, W. A. Ed.; Academic Press: New York, 1980; pp 23−
30. (c) Parker, V. D.; Tilset, M.; Hammerich, O. J. Am. Chem. Soc.
1987, 109, 7905. (d) Bordwell, F. G.; Cheng, J.-P.; Harrelson, J. A., Jr.
J. Am. Chem. Soc. 1988, 110, 1229. (e) Arnett, E. M.; Amarnath, K.;
Harvey, N. G.; Cheng, J.-P. Science 1990, 247, 423. (f) Bordwell, F. G.;
Zhang, X.-M. Acc. Chem. Res. 1993, 26, 510.
(4) For representative examples, see: (a) Serjeant, E. P.; Dempsey, B.
Ionisation Constants of Organic Acids in Aqueous Solution; Pergamon
Press: New York, 1979. (b) Stewart, R. The Proton Application to
Organic Chemistry; Academic Press: New York, 1985.
15825.
(13) Lehn, J. M. Acc. Chem. Res. 1978, 11, 49.
(14) Taft, R. W.; Bordwell, F. G. Acc. Chem. Res. 1988, 21, 463.
(15) It should be pointed out that fluorenes show a slightly different
acidity order than in Bm2imNTf2 > in BmpyNTf2 ≈ in BmimNTf2
(i.e., the pKa's in the latter two ILs are similar) because the greater
charge delocalization and the more hindered 9-carbon in fluorenide
ions attenuate their solvation with Bmim+ as compared that with
Bmpy+.
(16) The pKa value of 9-(p-bromophenylsulfonyl)-2-(phenylsulfonyl)
fluorene was determined in DMSO by the overlapping indicator
method.5a For other pKa values, see ref 5b and: (a) Troughton, E. B.;
Molter, K. E.; Arnett, E. M. J. Am. Chem. Soc. 1984, 106, 6726.
(b) Koppel, I. A.; Koppel, J.; Pihl, V.; Leito, I.; Mishima, M.; Vlasov, V.
M.; Yagupolskii, L. M.; Taft, R. W. J. Chem. Soc., Perkin Trans. 2 2000,
1125.
(17) (a) Koppel, I. A.; Taft, R. W.; Anvia, F.; Zhu, S.-Z.; Hu, L.-Q.;
Sung, K.-S.; DesMarteau, D.-D.; Yagupolskii, L. M.; Yagupolskii, Y. L.;
Ignat’ev, N. V.; Kondratenko, N. V.; Volkonskii, A. Y.; Vlasov, V. M.;
Notario, R.; Maria, P.-C. J. Am. Chem. Soc. 1994, 116, 3047.
(b) Bartmess, J. E. Negative Ion Energetics Data; Mallard, W. G.,
Linstrom, P. J., Eds.; NIST Chemistry WebBook, NIST Standard
Reference Database No. 69, August 1997, National Institute of
Standards and Technology, Gaithersburg MD, 20899 (http://
(5) (a) Matthews, W. S.; Bares, J. E.; Bartmess, J. E.; Bordwell, F. G.;
Cornforth, F. J.; Drucker, G. E.; Margolin, Z.; McCallum, R. J.;
McCollum, G. J.; Vanier, N. R. J. Am. Chem. Soc. 1975, 97, 7006.
(b) Bordwell, F. G. Acc. Chem. Soc. 1988, 21, 456 and references cited
therein.
(6) (a) Streitwieser, A.; Hammons, J. H.; Ciuffarin, E.; Brauman, J. I.
J. Am. Chem. Soc. 1967, 89, 59. (b) Bors, D. A.; Kaufman, M. J.;
Streitwieser, A. J. Am. Chem. Soc. 1985, 107, 6975. (c) Streitwieser, A.
J. Org. Chem. 2009, 74, 4433 and references cited therein.
(7) To name a few, see: (a) Coetzee, J. F.; Kolthoff, I. M. J. Am.
Chem. Soc. 1957, 79, 6110. (b) Arnett, E. M.; Burke, J. J. J. Am. Chem.
Soc. 1966, 88, 2340. (c) Ritchie, C. D.; Megerle, G. H. J. Am. Chem.
(18) Burrell, A. K.; Sesto, R. E. D.; Baker, S. N.; McCleskey, T. M.;
Baker, G. A. Green Chem. 2007, 9, 449.
(19) Bavin, P. M. G. Can. J. Chem. 1960, 38, 917.
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