Org. Synth. 1953, 33, 88
DOI: 10.15227/orgsyn.033.0088
Submitted by Robert E. Buckles and Norris G. Wheeler1.
Checked by T. L. Cairns and J. C. Lorenz.
1. Procedure
A 500-ml. three-necked flask is fitted with a reflux condenser and a thermometer, the bulb of which reaches far enough into the flask to be covered by the liquid. A solution of 46.0 g. (0.205 mole) of α-phenylcinnamic acid (p. 777) (Note 1) in 280 ml. (307 g., 2.38 moles) of quinoline (Note 2) is added to the flask along with 4.0 g. of copper chromite.2 The reaction flask is heated by means of a mantle or an oil bath until the temperature of the reaction mixture reaches 210–220°. The mixture is kept within this temperature range for 1.25 hours. The solution is then cooled immediately and added to 960 ml. of 10% hydrochloric acid in order to dissolve the quinoline (Note 3). The product is extracted from this mixture with two 200-ml. portions of ether followed by a 100-ml. portion. The combined ether extracts are filtered to remove particles of catalyst, washed with 200 ml. of 10% sodium carbonate, and dried over anhydrous sodium sulfate. The dry solution is removed from the drying agent by filtration and heated on a steam bath to distil the ether. The residue is dissolved in a hexane fraction, b.p. 60–72° (Skellysolve B); the solution is cooled to 0° and filtered to remove trans-stilbene, if any. The hydrocarbon solvent is removed by distillation, and the cis-stilbene is distilled. The yield is 23–24 g. (62–65%), b.p. 133–136° /10 mm., 95–97° /1 mm.; n25D 1.6183–1.6193, n20D 1.6212–1.6218 (Note 4).
2. Notes
1. The isomer of α-phenylcinnamic acid of m.p. 172–173° is used (p. 777). The isomer of m.p. 137–139° yields trans-stilbene on decarboxylation.3
2. Practical grade quinoline containing about 10% of isoquinoline and quinaldine can be used. If the quinoline contains water, the desired temperature can be reached by distillation of a small amount of quinoline directly from the reaction mixture.
3. The quinoline can be recovered by neutralization of the aqueous solution, extraction of the quinoline into ether, and distillation of the dried (over barium oxide) ether extract.
4. The product obtained from this type of decarboxylation is reported to contain only about 5% of trans-stilbene.4 A sample made according to the above directions can be treated with bromine in carbon tetrachloride at room temperature in the dark to give an 80–85% yield of the dl-dibromide which arises from trans addition to cis-stilbene. The meso-dibromide, which is very insoluble and easily separated, is obtained only to the extent of 10% or less. Part of the latter product may arise from the action of bromine atoms on cis-stilbene rather than from trans addition to trans-stilbene. The cis-stilbene prepared by this method is readily and completely soluble in cold absolute ethanol. It freezes solid at about −5°. Its ultraviolet absorption coefficient (ε) is 1.10 × 104 at 274 mμ and 8.7 × 103 at 294 mμ, quite different from trans-stilbene.
3. Discussion
cis-Stilbene has been prepared by the partial hydrogenation of tolan;5,6 by the electrolytic reduction of tolan;7 by the reduction of tolan with a copper-zinc couple;8 by the reduction of the low-melting isomer of α-bromostilbene with zinc dust in 90% alcohol;9 by the illumination of trans-stilbene with ultraviolet light;10 by the decarboxylation of the high-melting isomer of α-phenylcinnamic acid in the presence of barium hydroxide;3 by heating tolan with diisobutylaluminum hydride11 or zinc and acetic acid;12 and by the reaction of cis-bromostilbene with butyllithium followed by treatment with methanol.13 The present method is based on that of Taylor and Crawford.14
This preparation is referenced from:

References and Notes
  1. State University of Iowa, Iowa City, Iowa.
  2. Org. Syntheses Coll. Vol. 2, 142 (1943).
  3. Stoermer and Voht, Ann., 409, 36 (1915).
  4. Weygand and Rettberg, Ber., 73B, 771 (1940).
  5. Kelber and Schwarz, Ber., 45, 1946 (1912).
  6. Ott and Schröter, Ber., 60, 624 (1927).
  7. Campbell and Young, J. Am. Chem. Soc., 65, 965 (1943).
  8. Straus, Ann., 342, 238 (1905).
  9. Wislicenus and Jahrmarkt, Chem. Zentr., 1901 I, 463.
  10. Stoermer, Ber., 42, 4865 (1909).
  11. Wilke and Müller, Chem. Ber., 89, 444 (1956).
  12. Rabinovitch and Looney, J. Am. Chem. Soc., 75, 2652 (1953).
  13. Curtin and Harris, J. Am. Chem. Soc., 73, 4519 (1951).
  14. Taylor and Crawford, J. Chem. Soc., 1934, 1130.

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

copper-zinc couple

ethanol (64-17-5)

hydrochloric acid (7647-01-0)

acetic acid (64-19-7)

methanol (67-56-1)

ether (60-29-7)

sodium carbonate (497-19-8)

bromine (7726-95-6)

sodium sulfate (7757-82-6)

barium oxide

carbon tetrachloride (56-23-5)

zinc (7440-66-6)

barium hydroxide (17194-00-2)

Quinoline (91-22-5)



quinaldine (91-63-4)

butyllithium (109-72-8)

hexane (110-54-3)

isoquinoline (119-65-3)

diisobutylaluminum hydride (1191-15-7)

α-Phenylcinnamic acid (3368-16-9)

trans-Stilbene (103-30-0)

cis-Stilbene (645-49-8)