Organic Syntheses, Coll. Vol. 2, p.336 (1943); Vol. 18, p.47 (1938).
A 250-cc. flask, fitted with an inlet tube
reaching to the bottom, a thermometer
, and an exit tube for conducting away unused gas
, is immersed in an ice-water bath
, and to it is added 80 g. (0.69 mole) of freshly distilled indene (Note 1)
. While the temperature of the liquid is kept at 5–10°, dry hydrogen chloride
is passed in at a moderate rate until 24–27 g. of the gas has been absorbed. The addition takes from eight to ten hours and requires little attention from the operator. The crude α-chlorohydrindene
is then transferred to a 250-cc. Claisen flask
and distilled at diminished pressure. After a small fore-run (5–10 g.) containing indene
boiling at 90–103°/15 mm.
is collected; the yield is 80–90 g. (Note 2)
In a 500-cc. three-necked flask, fitted with a stirrer
, thermometer, and dropping funnel
, is placed 100 g. (1 mole) of chromic anhydride
dissolved in 100 cc. of water, and 100 cc. of glacial acetic acid
is added. The α-chlorohydrindene
is then admitted through the funnel at such a rate as to keep the temperature at 35–40°, the flask being cooled externally. This addition takes about one and one-half hours; after it is complete, stirring is continued for fifteen minutes before the mixture is poured into a large beaker
and diluted with 300 cc. of water. After the acid present is neutralized by the addition of solid sodium carbonate (Note 3)
, the α-hydrindone
is expelled from the mixture by steam distillation, care being taken to avoid entrainment of froth at the beginning of the process. When about 2.5 l. of distillate has been collected, the solution again begins to froth. The operation is stopped at this point, since further distillation does not yield an appreciable quantity of product. The α-hydrindone
usually solidifies, as soon as the distillate is chilled, to a mixture of colorless crystals and a yellow solid; the product is collected after thorough cooling in an ice bath
. This moist solid is dissolved in 200 cc. of benzene
, and the solution is subjected to distillation until free from water. After the benzene
is removed by vacuum distillation on the steam bath, the α-hydrindone
is distilled. It boils at 125–126°/17 mm.
, and the distillate is a pale yellow solid, m.p. 39–41°
. The yield is 46–55 g.
per cent of the theoretical amount, based on the indene
used) (Note 4)
and (Note 5)
If technical indene
is employed, the fraction boiling at 178–182° is suitable for the preparation. The checkers used indene
, b.p. 181.6–183.3°
, obtained from the Barrett Company, New York City.
Most of the material distils at 100–103°/15 mm., but the yield of α-hydrindone
is increased by using the material collected over the wider range.
An excess of sodium carbonate
promotes foaming during the distillation and is to be avoided. Since the neutral point is not easily recognized with test paper, the carbonate is added in decreasing amounts until a fresh portion is no longer decomposed with gas evolution.
It is not practicable to dry the steam-distilled product in the air because α-hydrindone
has such a high vapor pressure that the loss is appreciable. Drying can be accomplished in a vacuum desiccator
, but this takes several days. The distillation specified gives a completely anhydrous product with the loss of no more than 2–5 g.
Crystallization is conveniently accomplished by dissolving the α-hydrindone
in alcohol (1 cc. per gram) at room temperature, adding water until solid just begins to separate, and cooling to 0°. The substance crystallizes either as long plates or as leaflets.
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