Improvements in or relating to the preparation of alicyclic olefinic hydrocarbons

A cyclic mono-olefin is obtained from a corresponding cyclic polyolefin (containing all the double bonds in the ring) by forming a Diels-Alder adduct of the latter with a fused polycyclic aromatic hydrocarbon having two meso carbon atoms in a 1,4-relationship to each other, hydrogenating the olefinic bonds in the adduct and decomposing the hydrogenated adduct to recover the aromatic hydrocarbon and a cyclic olefin. Lists are given of polymers and aromatic hydrocarbons. The adduct is formed at 125-275 DEG C. and hydrogenated at 30-150 DEG C. and 50-5000 p.s.i. in the presence of 2-10% weight of Raney nickel based on adduct and in the presence, if desired, of a solvent such as benzene, toluene or paraffins. The hydrogenated adduct is pyrolysed at 275-450 DEG C. The examples describe the preparation of the new compounds which are adducts of anthracene with cyclooctadiene-1,5 or cyclododecatriene-1,5,9 and their hydrogenated derivatives and the recovery therefrom of cyclooctene and cyclododecene.