It is prepared by oxidation of indane or indene. The indenyl ligand is formally the anion derived from deprotonation of indene. It is usually produced by hydrogenation of indene. Notice the 5 membered pentyl chain on the 3-position of the indene ring. The principal industrial use of indene is in the production of indene/coumarone thermoplastic resins. Resins derived from Coumarone (Benzofuran) and indene are also produced. The sodio-indene is converted back to indene by steam distillation. Dehydration with HSO gives the indene ethanol 4. Oxidation of indene with acid dichromate yields homophthalic acid ("o"-carboxylphenylacetic acid). In Munich he conducted research on indene and received his PhD in 1889. Indene is a flammable polycyclic hydrocarbon with chemical formula CH.