Organic Syntheses, CV 6, 835
Submitted by W. J. Middleton
1 and E. M. Bingham.
Checked by Eugene R. Kennedy, Ronald F. Sieloff, and Carl R. Johnson.
1. Procedure
A
dry, 1-l., three-necked, round-bottomed flask is fitted with a
500-ml. dropping funnel,
thermometer, a
magnetic stirrer, and a
reflux condenser protected from the atmosphere with a
drying tube. The apparatus is flushed with dry
nitrogen, and
150 ml. of dry dichloromethane and
21 ml. (0.16 mole) of diethylaminosulfur trifluoride [
Org. Synth., Coll. Vol. 6, 440 (1988)] are added to the flask. The contents of the flask are cooled to 10°, and a solution of
23.0 g. (0.150 mole) of 4-nitrobenzyl alcohol (Note
1) in
450 ml. of dichloromethane is added dropwise at a fast rate (45 minutes). The reaction mixture is allowed to come to room temperature and poured into a
beaker containing 300 g. of ice, decomposing any unreacted
diethylaminosulfur trifluoride. The organic layer is separated, and the water layer is extracted twice with
45-ml. portions of dichloromethane. The organic layer and extracts are combined, washed with 150 ml. of water, and dried over anhydrous
magnesium sulfate. Evaporation to dryness under reduced pressure gives
20.9–22.1 g. (
90–95%) of crude product. Recrystallization from
500 ml. of pentane yields
15.5 g. (
67%) of
4-nitrobenzyl fluoride as colorless needle-shaped crystals, m.p.
36–37° (Note
2).
2. Notes
2. An additional quantity of product of lesser purity can be obtained as a second crop by evaporation of the
pentane.
3. Discussion
This procedure is an example of a broadly applicable, simple method for replacing the hydroxyl group of functionally substituted and unsubstituted primary, secondary, and tertiary alcohols with
fluorine.
Diethylaminosulfur trifluoride,
2 the fluorinating reagent used in this procedure, is less likely to cause rearrangements or dehydration than other reagents sometimes used for this purpose (SF
4, HF, HF·pyridine, SeF
4·pyridine, and (C
2H
5)
2NCF
2CHClF).
3 Furthermore,
diethylaminosulfur trifluoride is a liquid that can be measured easily and used in standard glass equipment at moderate temperatures and atmospheric pressure.
This preparation is referenced from:
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