Organic Syntheses, CV 4, 731
Submitted by Richard H. Wiley and Newton R. Smith
1.
Checked by Richard T. Arnold, William E. Parham, and Darwin D. Davis.
1. Procedure
A.
m-Nitrocinnamic acid. In a
1-l. round-bottomed flask fitted with a
reflux condenser are placed
151 g. (1 mole) of m-nitrobenzaldehyde (Note
1),
115 g. (1.1 moles) of malonic acid,
250 ml. of 95% ethanol, and
25 ml. of pyridine. The mixture is heated on a
steam bath under gentle reflux for 6–8 hours and cooled. The large masses of crystals are broken up with a
spatula, and the reaction mixture is cooled in an
ice bath. The solid is collected on a
Büchner funnel, and the residue is washed with
100 ml. of cold ethanol and then with two
100-ml. portions of ether. The crude
m-nitrocinnamic acid is suspended in
300 ml. of ethanol and digested on a steam plate for 2–3 hours. The mixture is cooled and filtered, and the solid is air-dried. The product,
144–155 g. (
75–80%), is a light-yellow solid and melts at
200–201° (Note
2).
B.
m-Nitrostyrene. In a
250-ml. two-necked flask equipped with a 250°
thermometer and an air condenser are placed
30 g. (0.155 mole) of m-nitrocinnamic acid,
2 g. of copper powder, and
60 ml. of dry quinoline (Note
3). The flask is heated with a
Bunsen burner to 185–195°, during which time a steady stream of
carbon dioxide is evolved. After 2–3 hours (Note
4), the reaction mixture is cooled and poured into a mixture of
75 ml. of concentrated hydrochloric acid and 175 g. of ice. The
m-nitrostyrene is isolated by steam distillation, approximately 1 l. of distillate being collected. The aqueous distillate is extracted with three
50-ml. portions of chloroform, which are combined and dried over anhydrous
sodium sulfate. A
50-ml. Claisen flask, equipped with a
dropping funnel, is heated on a steam bath, and the filtered
chloroform extract is added dropwise. Heating is continued until all the solvent has been removed. The residue is then distilled at 3–5 mm. pressure. Following a small fore-run of less than 1 g. (Note
5), the
m-nitrostyrene distils as a yellow liquid. The yield is
13–14 g. (
56–60%), b.p.
90–96°/3.5 mm.,
nD20 1.5836,
nD27 1.5800–1.5802 (Note
6) and (Note
7).
2. Notes
2. This procedure has been used by the submitters and others to prepare the following cinnamic acids from substituted benzaldehydes:
o-nitrocinnamic acid (
70%),
2 p-nitrocinnamic acid (
77%),
2 m-cyanocinnamic acid (
71%),
3 o-chlorocinnamic acid (
82%),
4 m-chlorocinnamic acid (
53%),
4 p-chlorocinnamic acid (
73%),
4 2,4-dichlorocinnamic acid (
70%),
4 3,4-dichlorocinnamic acid (
81%),
4 m-bromocinnamic acid (
31%),
4 p-methoxycinnamic acid (
60%),
4 and
3,4-dimethoxycinnamic acid (
77%).
4
The method constitutes a simple preparation of ethanol-insoluble cinnamic acids, of a high degree of purity when compared with the Perkin reaction
5 or the usual procedure for the Doebner reaction
(p. 327), which uses a large excess of
pyridine. A useful modification of this reaction is to warm the reactants on a steam plate in the absence of alcohol.
6,7
3.
Quinoline that has been purified by steam distillation of an acid solution should be used. Crude
quinoline sometimes contains non-basic, high-boiling impurities such as
nitrobenzene, which make the purification of
m-nitrostyrene more difficult.
4. The checkers obtained a lower yield (
9–11 g.) when a 2-hour heating period was used. The reaction must be carried out at 195° until the evolution of
carbon dioxide has practically ceased (usually 2.75 hours). The checkers used
Mallinckrodt copper powder.
5. The checkers obtained essentially no fore-run and only trace amounts of solid residue. The refractive index of the first 200 mg. was
nD27 1.5800; of the center fractions,
nD27 1.5802; and of the last 700 mg.,
nD27 1.5800.
7. Larger runs usually give smaller percentage yields.
3. Discussion
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