T. B. Phan, H. Mayr
FULL PAPER
tolyl)nitromethane (2e-H), (p-nitrophenyl)nitromethane (2f-H),
and (m-nitrophenyl)nitromethane (2g-H) were synthesized as pre-
viously reported.[24]
Rate constants for the individual kinetic experiments are given in
the Supporting Information.
Supporting Information (for details see the footnote on the first
page of this article): Determination of the acidities of 2d-H, 2e-H,
and 2h-H in methanol; details of the kinetic experiments.
(p-Cyanophenyl)nitromethane (2h-H):[39]
A mixture of tBuOK
(6.78 g, 60.4 mmol) and 18-crown-6 (3.05 g, 11.5 mmol) in dry
THF (200 mL) was cooled to –35 °C and a solution of 4-cyanotolu-
ene (6.01 g, 51.3 mmol) in dry THF (40 mL) was slowly added.
Subsequently, a solution of n-propyl nitrate (4.30 mL, 40.2 mmol)
in dry THF (10 mL) was added with vigorous stirring. After the
mixture had been stirred at –35 °C for 30 min, a solution of glacial
acetic acid (8.5 mL) in dry THF (20 mL) was added. The mixture
was stirred until it reached room temperature and was then poured
into water (200 mL) and extracted with diethyl ether (3×100 mL).
The combined organic phases were washed with water and dried
(Na2SO4), and the solvent was evaporated to give the crude product
as a light yellow solid (4.59 g, m.p. 93–95 °C). Crystallization gave
2h-H as a colorless solid [4.25 g, 65%, m.p. 95–96 °C (from
MeOH)]. 1H NMR (300 MHz, CDCl3): δ = 5.52 (s, 2 H, CH2NO2),
7.59 (d, J = 8.4 Hz, 2 H), 7.75 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR
(75.5 MHz, CDCl3): δ = 79.0 (t, CH2NO2), 114.1 (s, C-4), 117.8 (s,
CN), 130.7 (d, C-2,6), 132.8 (d, C-3,5), 134.0 (s, C-1) ppm.
C8H6N2O2 (162.15): C 59.26, H 3.73, N 17.28; found C 59.51, H
3.67, N 17.24.
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft (Ma
673–17) and the Fonds der Chemischen Industrie is gratefully ac-
knowledged. We thank Dr. T. Lemek for experimental support and
Dr. A. R. Ofial for helpful discussions.
[1] H. Mayr, T. Bug, M. F. Gotta, N. Hering, B. Irrgang, B. Janker,
B. Kempf, R. Loos, A. R. Ofial, G. Remennikov, H. Schimmel,
J. Am. Chem. Soc. 2001, 123, 9500–9512.
[2] a) H. Mayr, M. Patz, Angew. Chem. 1994, 106, 990–1010; An-
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Mayr, A. R. Ofial, in: Carbocation Chemistry (Eds.: G. A.
Olah, G. K. S. Prakash), Wiley, Hoboken, NJ, 2004, chap-
ter 13, pp. 331–358; d) H. Mayr, A. R. Ofial, Pure Appl. Chem.
2005, 77, 1807–1821.
[3] T. Lemek, H. Mayr, J. Org. Chem. 2003, 68, 6880–6886.
[4] a) F. Terrier, S. Lakhdar, R. Goumont, T. Boubaker, E. Buncel,
Chem. Commun. 2004, 2586–2587; b) F. Terrier, S. Lakhdar, T.
Boubaker, R. Goumont, J. Org. Chem. 2005, 70, 6242–6253.
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Mayr, J. Phys. Org. Chem. 2003, 16, 431–437.
[6] S. Minegishi, H. Mayr, J. Am. Chem. Soc. 2003, 125, 286–295.
[7] a) S. Minegishi, S. Kobayashi, H. Mayr, J. Am. Chem. Soc.
2004, 126, 5174–5181; b) T. B. Phan, M. Breugst, H. Mayr,
Angew. Chem., in press.
Kinetic Measurements: Solutions of the carbanions were freshly
generated prior to each kinetic measurement by mixing the CH
acidic compounds with methoxide in methanol.
The reactions of the colored reference electrophiles with carbanions
and with methoxide gave rise to colorless products, and the decays
in the absorptions of the electrophiles were followed by UV/Vis
spectroscopy.[6,19a,40,41] The temperature of the solutions during all
kinetic studies was kept constant (20.0 0.1 °C) by use of circulat-
ing bath thermostats.
[8] T. B. Phan, H. Mayr, Can. J. Chem. 2005, 83, 1554–1560.
[9] B. Kempf, H. Mayr, Chem. Eur. J. 2005, 11, 917–927.
[10] R. Loos, S. Kobayashi, H. Mayr, J. Am. Chem. Soc. 2003, 125,
14126–14132.
In general, Hi-Tech SF-61DX2 stopped-flow spectrophotometer
systems (controlled by Hi-Tech KinetAsyst2 software) with syrin-
ges set up for a 10:1 mixing ratio were used for investigation of the
reactions between carbanions and reference electrophiles. Only the
rates of the slow reactions between 2i and quinone methides 1f and
1g were determined by use of a J&M TIDAS diode array spectro-
photometer, which was controlled by Labcontrol Spectacle soft-
ware and connected to a Hellma 661.502-QX quartz Suprasil im-
mersion probe (5 mm light path) through fiber optic cables and
standard SMA connectors.
[11] A. A. Tishkov, H. Mayr, Angew. Chem. 2005, 117, 145–148;
Angew. Chem. Int. Ed. 2005, 44, 142–145.
[12] S. Minegishi, R. Loos, S. Kobayashi, H. Mayr, J. Am. Chem.
Soc. 2005, 127, 2641–2649.
[13] A. A. Tishkov, U. Schmidhammer, S. Roth, E. Riedle, H. Mayr,
Angew. Chem. 2005, 117, 4699–4703; Angew. Chem. Int. Ed.
2005, 44, 4623–4626.
[14] H. Mayr, G. Lang, A. R. Ofial, J. Am. Chem. Soc. 2002, 124,
4076–4083.
[15] H. Mayr, N. Basso, G. Hagen, J. Am. Chem. Soc. 1992, 114,
3060–3066.
The stopped-flow experiments were performed by mixing 10 vol-
ume parts of the solutions of the carbanions in methanol with 1
volume part of the solutions of the reference electrophiles in aceto-
nitrile to yield 91:9 (v/v) mixtures of methanol and acetonitrile.
[16] H. Mayr, N. Basso, Angew. Chem. 1992, 104, 1103–1105; An-
gew. Chem. Int. Ed. Engl. 1992, 31, 1046–1048.
[17] For a comprehensive compilation of data published until 2002
see ref.[2b]
.
Carbanion concentrations were at least ten times higher than those
of the electrophiles, resulting in pseudo-first-order kinetics with ex-
ponential decay of the electrophile concentrations. The pseudo-
first-order rate constants kobs (s–1) were obtained by least-squares
fitting of the single-exponential At = Aoexp(–kobst) + C to the time-
dependent absorbance A of the electrophiles.
[18] a) T. Tokuyasu, H. Mayr, Eur. J. Org. Chem. 2004, 2791–2796;
b) A. D. Dilman, H. Mayr, Eur. J. Org. Chem. 2005, 1760–1764.
[19] a) A. D. Dilman, S. L. Ioffe, H. Mayr, J. Org. Chem. 2001, 66,
3196–3200; b) B. Kempf, N. Hampel, A. R. Ofial, H. Mayr,
Chem. Eur. J. 2003, 9, 2209–2218.
[20] F. Dulich, K.-H. Müller, A. R. Ofial, H. Mayr, Helv. Chim.
Acta 2005, 88, 1754–1768.
As defined in Equation (9), the terms k2,MeO–[MeO–] were calcu-
lated from the known k2,MeO– (from ref.[8]) and then subtracted
from the pseudo-first-order rate constants kobs. The obtained values
k1Ψ (s–1) were plotted against the concentrations of the carbanions,
giving linear correlations with slopes corresponding to the second-
order rate constants of the reactions of carbanions with the refer-
ence electrophiles k2,C– (–1 s–1). This method is analogous to the
evaluation in references.[24,25]
[21] a) H. Mayr, K.-H. Müller, Collect. Czech. Chem. Commun.
1999, 64, 1770–1779; b) H. Mayr, O. Kuhn, C. Schlierf, A. R.
Ofial, Tetrahedron 2000, 56, 4219–4229.
[22] T. Bug, M. Hartnagel, C. Schlierf, H. Mayr, Chem. Eur. J. 2003,
9, 4068–4076.
[23] a) R. Lucius, H. Mayr, Angew. Chem. 2000, 112, 2086–2089;
Angew. Chem. Int. Ed. 2000, 39, 1995–1997; b) R. Lucius, R.
Loos, H. Mayr, Angew. Chem. 2002, 114, 97–102; Angew.
Chem. Int. Ed. 2002, 41, 91–95.
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