Organic Syntheses, Coll. Vol. 5, p.523 (1973); Vol. 48, p.80 (1968).
Caution! This preparation should be carried out in a hood
to avoid exposure to ammonia
A suspension of sodium amide (0.275 mole) (Note 1)
in liquid ammonia
is prepared in the following manner in a 1-l. three-necked flask
equipped with an air condenser (Note 2)
, a sealed mechanical stirrer
, and a dropping funnel
. Commercial anhydrous liquid ammonia (600 ml.)
is introduced by pouring from an Erlenmeyer flask (Note 3)
. To the stirred liquid ammonia
is added a small piece of sodium
. After the appearance of a permanent blue color (Note 4)
a few crystals of ferric nitrate hydrate (ca. 0.1 g.)
are added, followed by small pieces of freshly cut sodium (Note 5)
until 6.32 g. (0.275 g. atom) has been added. After all the sodium
is converted to the amide (Note 6)
, 42.0 g. (0.250 mole) of diphenylmethane (Note 7)
in 20 ml. of anhydrous ether
is added (Note 8)
. The deep red suspension is stirred for 15 minutes. n-Butyl bromide (37.6 g., 0.274 mole) (Note 7)
in 20 ml. of anhydrous ether
is then added dropwise with stirring. The ammonia
is allowed to evaporate (Note 9)
from the resulting gray suspension. Water (100 ml.) is added carefully (Note 10)
, then 100 ml. of ether
. The ethereal layer is separated, and the aqueous layer is extracted with two further 100-ml. portions of ether
. The combined ethereal extracts are dried over Drierite
and filtered, and the solvent is removed. The resulting liquid (54.5 g.
) is essentially pure 1,1-diphenylpentane (Note 11)
and (Note 12)
The liquid is distilled with the use of a Claisen distillation head
without a fractionating column
. The fraction, b.p. 138–139° (1.5 mm.)
1.5501, weighs 51.6 g.
) (Note 13)
The checkers used a dry-ice condenser
in place of the air condenser.
Dry commercial liquid ammonia
is conveniently transferred from the cylinder via an Erlenmeyer flask without cooling and without the use of a condenser.
A permanent blue color may not remain after the addition of one pellet of sodium
because of the presence of traces of moisture. Another pellet is added if necessary.
Conversion is indicated by the discharge of the blue color (ca.
30 minutes). The addition of another portion of ferric nitrate hydrate
will catalyze the conversion.
The checkers found it important to add the diphenylmethane
20 minutes); fast addition caused the reaction to get out of control.
is allowed to evaporate overnight. A steam bath
may be employed with care to facilitate the evaporation.
In the event of the presence of traces of unreacted sodium
on the flask, water is added initially with special care.
The purity of the 1,1-diphenylpentane
is attested by vapor-phase chromatography on a 5-ft. column of 10% Apiezon L on Celite
undergoes air oxidation,2
it appears to be stable in a stoppered flask under an inert atmosphere.
The checkers observed b.p. 127–129° (1.5 mm.)
4. Merits of the Preparation
This procedure illustrates a process which is general for 1,1-diphenyl substituted hydrocarbons. Diphenylmethane
has been alkylated3
with benzyl chloride
, benzhydryl chloride
, α-phenylethyl chloride
, β-phenylethyl chloride
, isopropyl chloride
, 2-ethylbutyl bromide
, and n-octyl bromide
in yields of 99
, and 99%
The present method is superior to earlier ones in that it is shorter, the chemicals are readily available, and high yields are obtained. The Gilman method8
affords a 74%
yield but a longer reaction time (1–2 days) and less readily available starting materials make it less convenient.
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