Organic Syntheses, CV 4, 953
Submitted by B. C. McKusick and L. R. Melby
1.
Checked by James Cason and Ralph J. Fessenden.
1. Procedure
Caution! Because
hydrogen cyanide is formed in this reaction, all operations up to the recrystallization of the product should be carried out in a good
hood. Contact of
tetracyanoethylene with the skin should be avoided.
A solution of
26.6 g. (28 ml., 0.22 mole) of N,N-dimethylaniline in
65 ml. of dimethylformamide is placed in a
250-ml. beaker clamped about 30 cm. above the base of a ring stand. The beaker is provided with a
mechanical stirrer and
thermometer. An
iron ring is attached to the ring stand below the beaker so that the temperature of the reaction mixture can be controlled by raising or lowering an
ice bath or hot
water bath. Recrystallized
tetracyanoethylene (p. 877) (25.6 g., 0.20 mole) is added in small portions over a period of about 5 minutes with good stirring. The rate of addition is such as to maintain the temperature at 45–50°, and occasional cooling with an ice bath may be necessary to keep the temperature within this range.
When all the
tetracyanoethylene has been added, the reaction mixture is stirred at 45–50° for 10 minutes, and heat is supplied as needed by a water bath.
p-Tricyanovinyl-N,N-dimethylaniline generally crystallizes out as a dark-blue solid during this period. At the end of the heating period, the mixture is chilled in an ice bath for 30 minutes. The tricyanovinyl compound is collected on a
Büchner funnel, pressed dry with the help of a filter dam, and washed successively with
20 ml. of methanol and
40 ml. of ether. It weighs
25–30 g. after being dried in air.
The crude product is purified by recrystallization from
160–180 ml. of acetic acid. The solution (Note
1) is allowed to cool slowly to room temperature, and
p-tricyanovinyl-N,N-dimethylaniline is collected on a Büchner funnel and washed successively with
20 ml. of methanol and
40 ml. of ether. The product,
23–26 g. (
52–58%), is obtained as dark-blue needles, m.p.
173–175° (Note
2).
2. Notes
1. The
acetic acid solution is so deep a red color that it is necessary to hold the flask over a bright light in order to determine when all the solid has dissolved. The solution will dye the skin with a fast red color.
2. Although the crystals have a very dark blue appearance, the solutions are deep red; in
acetone, λ
max 517 mμ (ε 41,500).
3. Discussion
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