Hydrodefluorination of pentafluoroacetanilide
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 11, November, 2009 2309
Preparative synthesis of partially fluorinated aromatic amines
8 and 9. 2,3,4,5ꢀTetrafluoroaniline (8). A flask equipped with a
thermometer, and gasꢀfreeing tube, a magnetic stirrer, and an
oil bath with a thermoregulator was filled with NiCl2•6H2O
(119 mg, 0.5 mmol), 2,2´ꢀbipyridine (156 mg, 1 mmol), MP
(10 mL), and water (2 mL). The reaction mixture was stirred for
1 h at 70 °C, then the first portion of zinc dust (1.87 g, 29 mmol)
was added, the mixture was additionally stirred for 10 min, and
pentafluoroacetanilide (2.25 g, 10 mmol) was added. The
reaction mixture was stirred for 4 h at 70 °C, and the next portion
of zinc (935 mg, 14 mmol) was added every hour. Totally 4.68 g
(72 mmol) of zinc dust were added. The reaction mixture was
diluted with water (50 mL), and the solid part was filtered off
and washed with water (2×10 mL). The product was washed
off from the solid phase with acetonitrile (2×20 mL). The solvent
was evaporated, and water (40 mL) and sodium hydroxide
(800 mg, 20 mmol) were added to the residue. The obtained
mixture was stirred for 1 h at ~20 °C. 2,3,4,5ꢀTetrafluoroaniline
was steamꢀdistilled off from the reaction mixture and extracted
with dichloromethane (3×10 mL), the extract was dried with
magnesium sulfate, and the solvent was distilled off in vacuo.
The yield was 1.16 g (61% based on pentafluoroacetanilide).
19F NMR (acetone), δ: –142.2 (ddd, 1 F, F(2), 3JF,F = 22.2 Hz,
This work was financially supported by the Presidium
of the Siberian Branch of the Russian Academy of Sciꢀ
ences (Program of Complex Integration Projects, Project
No. 5.8.5).
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3
5JF,F = 12.1 Hz, JH,F = 10.4 Hz); –159.9 (dd, 1 F, F(4),
3
3JF,F = 20.4 Hz, JF,F = 20.4 Hz); –162.8 (ddd, 1 F, F(5),
3JF,F = 18.5 Hz, 5JF,F = 17.7 Hz, 4JHF = 8.9 Hz); –177.4 (dddd,
3
3
4
1 F, F(3), JF,F = 21.7 Hz, JF,F = 21.9 Hz, JF,F = 7.7 Hz,
4JH,F = 7.7 Hz).
3,4,5ꢀTrifluoroaniline (9). A flask equipped with a thermoꢀ
meter, a gasꢀoutlet tube, a magnetic stirrer, and an oil bath
with a thermoregulator was filled with NiCl2•6H2O (119 mg,
0.5 mmol), phenanthroline (156 mg, 1 mmol), MP (10 mL),
and water (2 mL). The reaction mixture was stirred for 1 h at
70 °C, then the first portion of zinc dust (1.87 g, 29 mmol)
was added, the mixture was additionally stirred for 10 min, and
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reaction mixture was stirred for 6 h at 70 °C, adding the next
portion of zinc (935 mg, 14 mmol) every hour. In all 6.54 g
(100 mmol) of zinc dust were added. The reaction mixture was
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off from the solid phase with acetonitrile (2×20 mL). The solvent
was evaporated, and water (40 mL) and sodium hydroxide
(800 mg, 20 mmol) were added to the residue. The obtained
mixture was stirred for 1 h at ~20 °C. The product was steamꢀ
distilled off from the reaction mixture and extracted with
dichloromethane (3×10 mL), the extract was dried with magneꢀ
sium sulfate, and the solvent was distilled off in vacuo. The yield
was 1.05 g (71% based on pentafluoroacetanilide). 19F NMR
3
(acetone), δ: –136.6 (dd, 2 F, F(3), F(5), JF,F = 21.3 Hz,
3
3JH,F = 10.5 Hz); –178.9 (tt, 1 F, F(4), JF,F = 21.3 Hz,
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NMR spectra were recorded at the Center of Collective
Use "Chemical Service Center of SB RAS" (N. N. Vorozhꢀ
tsov Novosibirsk Institute of Organic Chemistry, Siberian
Branch of the Russian Academy of Sciences) with the
financial support from the Russian Foundation for Basic
Research (Project No. 08ꢀ03ꢀ01805).
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