Organic Syntheses, CV 5, 130
Submitted by A. B. Galun
1 and A. Kalir
2.
Checked by R. Breslow and H. T. Bozimo.
1. Procedure
A.
1-Phenyl-2,2,2-trichloroethanol. In a
1-l. round-bottomed-flask fitted with a mechanical stirrer, a
thermometer, and a
powder funnel is placed a solution of
212 g. (2.00 moles) of freshly distilled benzaldehyde in
400 g. (270 ml., 3.35 moles) of chloroform. The mixture is cooled in an
ice bath, and
123 g. of commercial powdered potassium hydroxide is added with stirring at such a rate that the temperature of the solution does not exceed 45° (1–1.5 hours). The reaction mixture is stirred and kept at 40–50° for an additional hour and then poured into a solution of
60 ml. of sulfuric acid in 3 l. of water. The resulting two-phase mixture is transferred to a
separatory funnel and extracted with three
250-ml. portions of chloroform (a small amount of insoluble, black resinous material is discarded). The combined organic layers are washed with three
100-ml. portions of aqueous 10% sodium carbonate, dried over anhydrous
magnesium sulfate, and filtered into a 1-l. flask. The solvent is removed under reduced pressure on a hot
water bath. The residue is transferred to a
250-ml. flask and distilled under reduced pressure to give
1-phenyl-2,2,2-trichloroethanol, b.p.
155–165° (26 mm.),
90–100° (0.5 mm.) (Note
1) and (Note
2). The yield is
170–180 g. (
38–40%).
B.
1-p-Bromophenyl-1-phenyl-2,2,2-trichloroethane. In a
500-ml. round-bottomed flask fitted with a mechanical stirrer, a
dropping funnel, and a thermometer are placed
136 g. (0.60 mole) of 1-phenyl-2,2,2-trichloroethanol and
120 g. (81 ml., 0.77 mole) of bromobenzene. The flask is cooled in an
ice-water bath, and a mixture of
120 ml. of concentrated sulfuric acid and
50 ml. of oleum (20% SO3) is added with stirring at such a rate that the temperature of the reaction mixture does not exceed 10° (
ca. 45 minutes) (Note
3). The mixture is stirred for another 30 minutes at 10° and for 4–5 hours at room temperature. It is then poured with manual stirring onto 1 kg. of cracked ice, and the mixture is allowed to stand overnight. The precipitate (Note
4) is filtered, washed with water, and recrystallized from
300 ml. of ethanol (Note
5). The yield is
129–162 g. (
59–74%), m.p.
95–96° (Note
6).
C.
p-Bromodiphenylmethane. A
2-l. three-necked flask fitted with a
distillation condenser, a thermometer, and an
efficient mechanical stirrer is charged with
1.1 l. of diethylene glycol (Note
7) and a solution of
190 g. of potassium hydroxide in 100 ml. of water. The mixture is stirred, and water is distilled until the internal temperature reaches 180°. The resulting solution is allowed to cool to 100° or below, and
146 g. (0.40 mole) of 1-p-bromophenyl-1-phenyl-2,2,2-trichloroethane (Note
8) is added. The condenser is set for reflux, and the mixture is stirred and heated to boiling for 5 hours (Note
9). The hot solution is then poured onto 3 kg. of cracked ice, and the mixture is allowed to stand overnight. The oily layer is separated and dissolved in
ether (any insoluble material is discarded), and the aqueous layer is extracted with
250 ml. of ether. The combined ethereal solution and extracts are dried over
calcium chloride and filtered. The
ether is removed under reduced pressure on a hot water bath. The product is distilled under reduced pressure; b.p.
120–130° (3 mm.),
155–163° (13 mm.) (Note
10),
n24D 1.6028,
d2424 1.342. The yield is
74–79 g. (
75–80%) (Note
11).
2. Notes
1. The purpose of the distillation is to separate the product from tars. Therefore no fractionation is required, and the distillation may be carried out rapidly.
2. The carbinol, which has a tendency to supercool, may crystallize overnight; m.p.
38°.
3. Solid material is sometimes deposited on the walls of the reaction flask.
4. In some cases the organic layer separates as an oil; it is then obtained in crystalline form by trituration with
200 ml. of cold methanol, which dissolves the excess of
bromobenzene.
5. Wet material may require larger amounts of
ethanol.
6. Trituration of the crude precipitate with
methanol gives a
90% yield of material, m.p.
90–93°.
8. The material should be thoroughly freed of alcohol, preferably over
phosphorus pentoxide under reduced pressure, before use. Even traces of alcohol may reduce the yield to
60%.
9. The temperature of the refluxing solution should be above 165°. Efficient stirring is essential; otherwise the precipitating
potassium carbonate entrains much material, causing reduction of yield.
10. Good fractionation is not required.
11. Runs on a fourfold scale give the same yield.
3. Discussion
4. Merits of the Preparation
In this method inexpensive, commercially available chemicals are used as starting materials. The operations are simple, the yields acceptable, and the final products are free of isomers.
This procedure is especially suited for preparing variously substituted diarylmethanes.
6 The 1,1-diaryl-2,2,2-trichloroethanes may be converted to the corresponding benzophenones via the 1,1-diaryl-2,2-dichloroethylenes
7 and to 1,1-diarylacetic acids.
8
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