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Org. Synth. 1966, 46, 93
DOI: 10.15227/orgsyn.046.0093
PERCHLOROFULVALENE
[Bicyclopentadienylidene, octachloro-]
Submitted by V. Mark1
Checked by M. Rosenberger and Peter Yates.
1. Procedure
A slurry of 47.5 g. (0.100 mole) of decachlorobi-2,4-cyclopentadienyl (Note 1) in 200 ml. of petroleum ether (b.p. 30–60°) is prepared in a 1-l., three-necked, round-bottomed flask equipped with a Hershberg stirrer, thermometer, dropping funnel, and air condenser fitted with a drying tube. The reaction flask is immersed in a water bath at 20–24° and the stirrer is started. A solution of 25.2 g. (0.121 mole) of triisopropyl phosphite (Note 2) in 25 ml. of petroleum ether (b.p. 30–60°) is added from the dropping funnel at such a rate that the temperature of the mildly exothermic reaction remains between 20° and 25°. During the addition, which requires 50–80 minutes, the light yellow slurry of the starting material is converted to a dark blue slurry of perchlorofulvalene.
After the addition is completed, the reaction mixture is stirred for an additional period of 20 minutes. The crystalline product is filtered rapidly by suction through a sintered-glass funnel (Note 3) and rapidly washed with three 20-ml. portions of petroleum ether (b.p. 30–60°). After the last washing, the perchlorofulvalene is allowed to dry at room temperature. The yield of the dark bluish-violet, uniform crystals is 26–29 g. (65–72%). The chlorocarbon is of a high purity, as indicated by infrared and ultraviolet spectroscopy (Note 4); it can be recrystallized from benzene, cyclohexane, hexane, carbon tetrachloride, or methylene chloride without appreciable lowering of the yield.
2. Notes
1. Decachlorobi-2,4-cyclopentadienyl [bis-(pentachlorocyclopentadienyl)], m.p. 123–124°, can be obtained from Columbia Organic Chemicals Co., Inc., and Aldrich Chemical Co., Inc. The checkers used purified material, m.p. 124–126°, obtained by recrystallization of commercial material from hexane. They found that without prior purification of the commercial starting materials or correction for assay (cf. (Note 2)) the yield was reduced to 50%. The checked runs were carried out under nitrogen, but it was not determined whether this influenced the yield.
2. Triisopropyl phosphite can be obtained from Virginia Carolina Chemical Corporation, Eastman Organic Chemicals, Aldrich Chemical Company, Matheson Coleman and Bell, and K and K Laboratories. The presence of diisopropyl hydrogen phosphite or triisopropyl phosphate is not deleterious, but a correction for the assay is required. Fractionation readily separates triisopropyl phosphite, b.p. 60–61° (10 mm.), from diisopropyl hydrogen phosphite, b.p. 70–71° (10 mm.), and triisopropyl phosphate, b.p. 95–96° (10 mm.). The checkers used a fraction, b.p. 85–88° (33 mm.) (cf. (Note 1)).
Alternatively, triethyl phosphite (available from the suppliers given above) can be substituted, in equivalent amount, for triisopropyl phosphite; the yield of perchlorofulvalene is 55–60%. The use of trimethyl phosphite gives lower yields (45–48%) and a less pure product.
3. The use of a large-size (500-ml.), coarse-grade, sintered-glass funnel permits rapid filtration and the washing of the filter cake directly in the funnel. Rapid removal of the co-product, diisopropyl phosphorochloridate, (C3H7O)2P(O)Cl, from perchlorofulvalene is necessary in order to prevent its hydrolysis to petroleum ether-insoluble products.
4. Since perchlorofulvalene does not melt below its decomposition point around 200°, infrared and ultraviolet spectroscopic analyses provide the most satisfactory method of checking the purity of the product. The characteristic infrared maxima of perchlorofulvalene occur at 6.55, 7.56, 7.97, 8.10, 8.63, 10.37, 13.03, 14.24, and 14.53 μ, and the ultraviolet and visible maxima at 386 mμ (ε 35,800) and 590 mμ (ε 505). The absence of decachlorobi-2,4-cyclopentadienyl in the product is indicated by the absence of its characteristic bands at 6.27, 12.35, and 14.83 μ.
3. Discussion
The present procedure is that described by the submitter.2 Perchlorofulvalene has also been obtained by the dechlorination of decachlorobi-2,4-cyclopentadienyl catalytically at 500° and 0.1 mm. in 57% yield,3 or by a mixture of iron and ferric chloride in warm tetrahydrofuran in 14% yield4 or by stannous chloride in refluxing acetone in 36% yield.5 6
4. Merits of the Preparation
Perchlorofulvalene and the more recently prepared perbromofulvalene7 are the only stable compounds known at present in which the fulvalene system alone represents all the unsaturation. The current listing of a compound as "perchlorofulvalene" in various chemical catalogs is based on earlier work shown to be in error;2 this compound has been shown to be a C15Cl12 chlorocarbon with a trindane skeleton.2
Perchlorofulvalene is a highly reactive chlorocarbon which undergoes a variety of reactions, including dimerization and oligomerization8 and other addition reactions, including chlorination,6 (2+4)-cycloadditions,8 and reaction with nucleophiles.8 It has a unique structure9 which reflects a compromise between steric hindrance and conjugation. More recently its dipole moment10 and nqr spectrum11 have been determined.

References and Notes
  1. General Electric, Plastics Department, Mt. Vernon, Indiana 47620.
  2. V. Mark, Tetrahedron Lett., 333 (1961); V. Mark, U.S. Patent 3,328,472 (1967).
  3. A. E. Ginsberg, P. Raatz, and F. Korte, Tetrahedron Lett., 779 (1962).
  4. R. R. Hindersinn, U.S. Patent 3,475,502 (1969).
  5. D.C.F. Law, Ph.D. Thesis, The University of Wisconsin, 1966;
  6. R. M. Smith and R. West, J. Org. Chem., 35, 2681 (1970).
  7. P. T. Kwitowski and R. West, J. Am. Chem. Soc., 88, 4541 (1966); R. West and P. T. Kwitowski, J. Am. Chem. Soc., 90, 4697 (1968).
  8. V. Mark, unpublished results.
  9. P. J. Wheatley, J. Chem. Soc., 4936 (1961).
  10. I. Agranat, H. W. Feilchenfeld, and R. J. Loewenstein, Chem. Comm., 1154 (1970).
  11. I. Agranat, D. Gill, M. Hayek, and R. J. Loewenstein, J. Chem. Phys., 51, 2756 (1969).

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

petroleum ether

Benzene (71-43-2)

iron (7439-89-6)

carbon tetrachloride (56-23-5)

nitrogen (7727-37-9)

stannous chloride

cyclohexane (110-82-7)

acetone (67-64-1)

ferric chloride (7705-08-0)

methylene chloride (75-09-2)

Tetrahydrofuran (109-99-9)

hexane (110-54-3)

triisopropyl phosphite (116-17-6)

Triethyl phosphite (122-52-1)

diisopropyl hydrogen phosphite

trimethyl phosphite (121-45-9)

Perchlorofulvalene,
Bicyclopentadienylidene, octachloro- (6298-65-3)

decachlorobi-2,4-cyclopentadienyl

triisopropyl phosphate

diisopropyl phosphorochloridate

perbromofulvalene