Organic Syntheses, CV 5, 66
Submitted by George A. Olah and Stephen J. Kuhn
1.
Checked by John A. Dupont and William D. Emmons.
1. Procedure
Caution! Anhydrous
hydrogen fluoride is toxic and in contact with skin can cause serious burns. This preparation should be carried out in a
well-ventilated hood. Rubber gloves and safety goggles should be worn by the operator. In case of contact with
hydrogen fluoride wash the affected skin area immediately with copious amounts of water, and apply a
calcium gluconate paste (Note
1).
Hydrogen fluoride (50 g., 2.5 moles) is distilled from the
cylinder through a polyethylene tube into a 250-ml. polyethylene transfer bottle which has been previously weighed and calibrated. A vent is provided during this process by inserting a large-gauge hypodermic needle through the bottle cap. No provision against atmospheric moisture is necessary. The bottle is cooled in a
dry ice-acetone bath, and
45–50 ml. of liquid hydrogen fluoride is collected. The amount of liquid obtained can be determined by weight difference; however, since an excess of
hydrogen fluoride is employed, the exact weight need not be determined. The time required for collection of the
hydrogen fluoride can be appreciably shortened by placing the cylinder in a
pan of warm water.
The reaction itself is carried out in a
1-l. polyolefin bottle (Note
2) or
fused silica flask (Note
3) fitted with an
inlet tube (Note
4) leading to the bottom of the reaction vessel and a
reflux condenser which is connected to a
hydrogen chloride absorber or which leads directly to the hood. A condenser suitable for work with anhydrous
hydrogen fluoride can easily be prepared from a
glass-jacketed polyolefin, Teflon®, silica, or copper tube (Note
5).
Benzoyl chloride (281 g., 2.0 moles) is placed in the reaction vessel, and the
hydrogen fluoride gas is then introduced by its distillation from the transfer bottle through the inlet tube. Prior to this distillation the hypodermic needle is closed off by a metal cap. The
hydrogen fluoride is added over a period of approximately 1 hour. Generally, external cooling is not needed, as the evaporating
hydrogen chloride cools the reaction mixture. When the addition is completed, the reaction mixture is warmed to 30–40° and kept at this temperature for 1 hour. The mixture is then washed in an ordinary
glass separatory funnel (Note
6) with 500 ml. of ice water in which
12.5 g. (0.2 mole) of boric acid is dissolved (Note
7). The organic layer is quickly separated, and to it are added
10 g. of anhydrous sodium fluoride and
10 g. of anhydrous sodium sulfate (Note
7). The mixture is allowed to stand for 30 minutes and is then filtered and distilled through a
short Vigreux column. The yield of
benzoyl fluoride b.p.
159–161°,
n15D 1.4988 (Note
8), is
187–200 g. (
75–80%).
2. Notes
1. An alternative treatment which has been used with good results at Rohm and Haas Company is, after throughly washing the exposed area with tap water, to soak the burned area in an ice-cold 0.2% solution of Hyamine 1622 (a product of Rohm and Haas Company) in
70% aqueous ethanol for 1 hour. It has also been stated that soaking the affected area with ice and water for 1 hour is almost as effective.
2
2. Polyolefin bottles of suitable size are commercially available. One inconvenience occasionally observed with bottles which have not previously been in contact with
hydrogen fluoride is the formation of a slight pink color in the reaction mixture, possibly due to the plasticizers. This coloration does not affect either the yields or the purity of the product, however, because the color is generally eliminated after the product is washed and treated with
sodium fluoride.
3. No color problem exists when fused silica equipment, preferably with normal joints lubricated with a fluorinated grease, is used.
4. The inlet tube can be either polyolefin, Teflon
®, fused silica, or
copper.
5. Silica or
copper gives much better heat transfer than do plastic tubes. The checkers found, however, that the use of a condenser was superfluous and that substitution of a simple polyethylene tube long enough to vent the off-gas away from the operator and apparatus was quite satisfactory.
6. Although some slight etching can take place, at this stage glass equipment is entirely safe, and no contamination of the product occurs.
8.
Benzoyl fluoride is a potent lachrymator and is undoubtedly toxic. It is advisable to rinse all glassware with
acetone followed by
10% aqueous ammonia before removing the glassware from the hood.
3. Discussion
4. Merits of the Preparation
The described procedure, first applied by Colson and Fredenhagen,
3,4 is useful for the preparation of a wide variety of acyl fluorides.
5 The yields are normally 80–90%. Some examples of acyl fluorides prepared are listed in Table I.
Benzoyl fluoride can also be employed as a convenient source of acyl fluoride by reaction with
acetic acid.
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This preparation is referenced from:
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