Title: Cyclopentadiene
CAS Registry Number: 542-92-7
CAS Name: 1,3-Cyclopentadiene
Molecular Formula: C5H6
Molecular Weight: 66.10
Percent Composition: C 90.85%, H 9.15%
Literature References: Obtained from the distillates produced in carbonization of coal, esp from the foreruns of coke-oven light oil: Ward, US 2211038 (1940); process involving the liquefaction of coke-oven gas: Horclois, Chim. Ind. (Paris), special issue April 1934, pp 357-363. Also obtained during the cracking of petr hydrocarbons: Tropsch et al., Ind. Eng. Chem. 30, 169 (1938); cf. Dedussenko, J. Gen. Chem. USSR 7, 1467 (1937); Chem. Zentralbl. 109, I, 793 (1938). Synthesis by passing vaporized cyclopentane over activated alumina and oxides of molybdenum, chromium, or vanadium: Grosse et al., Ind. Eng. Chem. 32, 309 (1940); US 2157202; US 2157203; US 2157939. Lab prepn by depolymerization of dicyclopentadiene: Moffett, Org. Synth. coll. vol. IV, 238 (1963). Toxicity study: Smyth et al., Arch. Ind. Hyg. Occup. Med. 10, 61 (1954). Review and discussion of structure: Wilson, Wells, Chem. Rev. 34, 1 (1944). Review: M. Fefer, A. B. Small in Kirk-Othmer Encyclopedia of Chemical Technology vol. 7 (Wiley-Interscience, New York, 3rd ed., 1979) pp 417-429.
Properties: Liquid. d40 0.8235; d410 0.8131; d420 0.8021; d425 0.7966; d430 0.7914. mp -85°. bp760 41.5-42.0°. nD16 1.44632. Absorption spectum: Pickett et al., J. Am. Chem. Soc. 63, 1073 (1941). Insol in water. Miscible with alc, ether, benzene, carbon tetrachloride. Sol in carbon disulfide, aniline, acetic acid, liquid petrolatum. Cyclopentadiene polymerizes to dicyclopentadiene on standing. Polymerization is accelerated by the presence of peroxides or trichloroacetic acid. The dimer is cryst, mp 32.5°, with a camphor-like odor, having the structure of a partially hydrogenated indene contg a bridged methylene group. It is a more convenient form in which to handle cyclopentadiene, and is easily depolymerized by distilling at atmospheric pressure. LD50 of dimer orally in rats: 0.82 g/kg (Smyth).
Melting point: mp -85°; mp 32.5°
Boiling point: bp760 41.5-42.0°
Index of refraction: nD16 1.44632
Density: d40 0.8235; d410 0.8131; d420 0.8021; d425 0.7966; d430 0.7914
Toxicity data: LD50 of dimer orally in rats: 0.82 g/kg (Smyth)
CAUTION: Potential symptoms of overexposure are irritation of eyes and nose. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 86.
Use: Manuf resins; in organic synthesis as the diene in the Diels-Alder reaction producing sesquiterpenes, synthetic alkaloids, camphors.

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