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Org. Synth. 1970, 50, 36
DOI: 10.15227/orgsyn.050.0036
cis-3,4-DICHLOROCYCLOBUTENE
[Cyclobutene, 3,4-dichloro, cis-]
Submitted by R. Pettit1 and J. Henery.
Checked by J. Napierski and R. Breslow.
1. Procedure
Dry chlorine gas is admitted into a solution of 104 g. (1.00 mole) of cycloöctatetraene in 150 ml. of dry carbon tetrachloride contained in a tared, 500-ml., three-necked flask equipped with a gas-inlet tube, a low-temperature thermometer, and a calcium chloride drying tube. The reaction mixture is maintained between −28° and −30° throughout the addition, which is terminated after 71 g. (1.0 mole) of chlorine has been added. After the addition, which takes approximately 1 hour, the reaction mixture is allowed to warm to 0° and 50 g. of powdered sodium carbonate is added, and the contents are shaken gently for several minutes. This treatment removes any hydrochloric acid which may have been produced during the reaction. The mixture is then filtered directly into a 1-l., round-bottomed flask containing 135 g. (0.951 mole) of dimethyl acetylenedicarboxylate. A condenser is fitted to the flask and the solution is heated at gentle reflux for 3 hours (Note 1). The solvent is removed under reduced pressure (Note 2). The crude Diels-Alder adduct, which will slowly solidify on standing, is used directly in the next step.
The crude Diels-Alder adduct is transferred to a 500-ml., pressure-equalizing dropping funnel attached to a 1-l., three-necked, round-bottomed flask; the latter is immersed in an oil bath maintained at 200° and equipped with a distillation head, condenser, and receiving flask. The pressure inside the equipment is reduced to 20 mm. A magnetic stirrer in the pyrolysis flask is started, the Diels-Alder adduct (Note 3) is added slowly to the hot flask, and the pyrolysate collected in the receiving flask. The distillation temperature during the pyrolysis varies from 135° to 152°, depending on the rate of addition of the Diels-Alder adduct. After the addition is complete (about 1 hour), the pyrolysis is continued for a further 30 minutes or until very little material remains in the pyrolysis flask (Note 4). The crude pyrolysate is then redistilled at 12–15 mm., with all material boiling below 140° collected; this distillate consists mainly of a mixture of dichlorocyclobutene and 1,4-dichlorobutadiene, the residue being mainly dimethylphthalate.
A Final distillation at 55 mm. through a 36-in., platinum spinning band column yields 49–52 g. (40–43%) of pure cis-3,4-dichlorocyclobutene (b.p. 70–71°, 55 mm.); the forerun (b.p. 58–62°, 55 mm.) consists mainly of 1,4-dichlorobutadiene (Note 5).
2. Notes
1. The reaction is very exothermic and usually it is necessary to remove the external source of heat for a short period as soon as reflux has started.
2. Slight warming and pressures of about 1 mm. are required to remove the last of the solvent.
3. A sun lamp situated close to the funnel may be required to prevent solidification of the Diels-Alder adduct.
4. It is necessary to keep the internal pressure close to 20 mm. (place a manometer in the line). If lower pressures are used, the Diels-Alder adduct itself will distill over; if higher pressures are maintained, the rate of removal of the dichlorocyclobutene from the hot reaction flask is reduced and extensive thermal rearrangement to 1,4-dichlorobutadiene will occur.
5. A good fractionating column is required to separate the 1,4-dichlorobutadiene from the dichlorocyclobutene. At 55 mm. the dichlorobutadiene will distill at 58–62°; after this material has been removed, the temperature will rise fairly sharply to 70°, and at this point the reflux ratio may then be reduced from 10:1 to zero and the dichlorocyclobutene collected quickly. It usually is necessary to apply heat frequently with a sun lamp to prevent solidification of the dichlorobutadiene in the exit tube of the distillation apparatus, especially if the receiving flask is kept cold.
3. Discussion
This method of preparation, due to Nenitzescu, Avram, Marica, Dinulescu, Farcasiu, Elian, and Mateescu,2 is the only practical method available at this time for the preparation of 3,4-dichlorocyclobutene.
This preparation is referenced from:

References and Notes
  1. Deceased, December 10, 1981; work done at Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712.
  2. M. Avram, E. Marica, I. Dinulescu, M. Farcasiu, M. Elian, G. Mateescu, and C. D. Nenitzescu, Chem. Ber., 97, 372 (1964).

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

hydrochloric acid (7647-01-0)

sodium carbonate (497-19-8)

carbon tetrachloride (56-23-5)

chlorine (7782-50-5)

Dimethyl acetylenedicarboxylate (762-42-5)

dichlorocyclobutene

3,4-dichlorocyclobutene

1,4-dichlorobutadiene

dimethylphthalate

dichlorobutadiene

cyclooctatetraene

cis-3,4-Dichlorocyclobutene,
Cyclobutene, 3,4-dichloro, cis- (2957-95-1)