Preparation of Cyclopentadiene from its Dimer In many teaching and research laboratories, cyclopentadiene is prepared a t frequent intervals by cracking dicyclopentadiene either neat1 or by adding i t to a high-boiling aiL2Recently a vapor-phase pyrolytic method has been d e s ~ r i b e d . ~ T h e formation of veroxides in the starting.material is a hazard that must be avoided, and the accumulation of viscous smelly residues is a wasteful and unpleasant consequence of these methods. We have used a convenient procedure published in 1927 by workers of thePhilippineHealth Service attheculion Leper Colony4and referred tahut not recommended by Moffet.' In a fume hood, dieyclopentadiene is first freed from peroxides by passage through a short column of activated alumina using a small pressure of nitrogen t o increase the flow rate if necessary. Iron filings are added to the dicyclopentadiene in a flask fitted with a fractionating column and condenser set for distillation. The flask is heated to 16Cb170 OC and the quantity of cyclopentadiene (bp 42 'C) required is distilled and collected in aflask protected witha drying tubeand cooled withice-salt. The cyclopentadiene dimerizesslowly (tm= 12 h a t roam temperature) and should be used without delay. It is also highly flammable, and both when heating is hegun and when the distillation flask is cooled the apparatus contains a mixture of dime and air. It is prudent practice to place a durine" the amration. After eooline. the aooaratus is sealed and stored in the ~rotectivescreen in front of the amaratus . dark The visrosity o i the laluid rrrnainina in the rrartron flaak does not inrrrase with tirnr nnd oploprnmdiene can be ~l~\tiliwl f n m the tlosk nt intervals tur rnunths. 'The rlaik can also he topped up with fresh diqrlopcntndiene u,irhout dungw.'rhe liquid in the flask goesn deepurangc-hrown color and examination hy thin layer uhrumatogmphy shows this t o be due to the formation of a number of products hut not ferrocene. ~
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' Moffet, R. B. Organic Syntheses 1883.4, 238. '
Kirk-Othmer Encycl. Chem. Techno!., 3rd ed.: 1979, 7,417. Magnusson, G. J. Org. Chem. 1985, 50, 1998. Peerkins, G. A,; Cruz, A. 0 . J. Am. Chem. Sac. 1927, 49, 517
Ronald S. Dlckson, Bruce J. Dobney, and Frank W. Eastwood Monash University
Clayton, Vic. 3168. Australia
898
Journal of Chemlcal Education
