Formaldehyde solution equivalent to
60 g. of formaldehyde (2 moles) (Note
1) and
8 g. of potassium bicarbonate (small crystals) are placed in an
800-ml. beaker standing in a
water bath at 20° in a
hood. Mechanical stirring is started and
160 g. (1 mole) of diethyl malonate (Note
2) is added dropwise during about 40–50 min., at such a rate that the temperature of the reaction mixture is held at 25–30°. Stirring is continued for 1 hour. The reaction mixture is transferred to a
separatory funnel. A saturated solution of
ammonium sulfate (320 ml.) (Note
3) is added and the mixture is extracted with
320 ml. of ether. The ethereal extract, dried for 1 hour with anhydrous
sodium sulfate (20 g.), is filtered into a
1-l., three-necked flask through a
fluted filter paper. The
sodium sulfate and paper are washed with
50 ml. of anhydrous ether. The flask (fitted with a
thermometer reaching to the bottom, a condenser set for downward distillation; third neck closed) is placed in a suitable heating bath (Note
4). Boiling chips are introduced and the ether is distilled until the temperature of the liquid has risen to 45–50°. The heating bath is then removed and the distillation assembly is replaced by a glass tube (about 4 mm. I.D.) reaching to the bottom of the flask and closed by a piece of rubber tubing and a screw clamp. An aspirator is now connected to the third neck of the flask. Vacuum is applied and volatile material is removed until the pressure falls to 20–30 mm. The temperature of the contents of the flask is brought to 40° and maintained there until crystallization begins and for an additional 30 minutes (Note
5).
Isopropyl ether (500 ml.) (Note
6) is added. The mixture is warmed to 50° and swirled until the product (crystalline and oily) dissolves. The solution is transferred to an
Erlenmeyer flask, and cooled in ice water with stirring until a thick suspension of crystals results. The suspension is refrigerated for 1 hour, filtered with suction (
rubber dam), and the crystals are dried overnight at room temperature, and then in a
vacuum desiccator over
sulfuric acid. The yield of colorless crystals, m.p.
48–50°, is
158–166 g. (
72–75%). This product may be recrystallized from
isopropyl ether (3.5 volumes) with an
85% recovery to yield material with m.p.
50–52°. Melting points of
52–53° and
52° are reported.
2,3