Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

ACBTYLACBTONB. BBNZOYLACBTONB 253
mide has been added, the flask is allowed to stand, first in ice-water
for two hours with frequent shaking, and then for twelve hours at
room temperature. Ice and cold water (100 g. of each) are then successively
added and, after the ethyl acetate which remains has been
separated, the aqueous layer is made just acid by addition of dilute
acetic acid. From the solution thus obtained the acetylacetone is
precipitated as copper salt by means of saturated aqueous copper
acetate solution. Finely powdered copper acetate (40 g.) is dissolved
in the necessary amount of boiling water. If basic copper acetate is
present, a small amount of acetic acid is added. The solution is used
while still lukewarm, before the salt crystallises again.
After some hours the blue-green compound of copper and acetylacetone
is separated by filtration with suction, washed twice with
water, transferred directly from the filter funnel to a separating
funnel, and, after being covered with ether, decomposed by continuous
shaking with 50 c.c. of 4iV-sulphuric acid. The ethereal
solution is separated and the acid layer is extracted with ether ; the
extract is then combined with the ethereal solution, which is now
dried over calcium chloride. After the ether has been removed by
distillation the diketone is likewise distilled. The bulk of the
material passes over at 125°-140° and, on repeating the distillation,
at 135°-140°. The boiling point of the completely pure substance
is 139°. Yield 15-20 g.
If the distillation is carried out under reduced pressure (about
50 mm. reduction), a purer and also more stable product is obtained.
Experiment.-—One drop of ferric chloride solution is added to a few
drops of an aqueous solution of acetylacetone. The reaction characteristic
of enols takes place. If now the solution is cooled in ice
and dilute bromine water is rather quickly added, the red colour of
the iron enolate disappears for a short time and then returns rapidly.
Benzoylacetone. — C6H5.CO.CH2.CO.CH3 is prepared in an
analogous way from acetophenone and ethyl acetate according to
the procedure of Claisen, Ber., 1905, 38, 695. The yield may be as
much as 75 per cent of the theoretical. The cheaper converse
method-—action of sodamide on ethyl benzoate and acetone-—also
succeeds in this case, although it fails when sodium or sodium
ethoxide is used as condensing agent. In general the use of sodamide
is to be preferred in the synthesis of 1 : 3-diketones.