Indene dimerization products

The reaction of 1H-indene (indene) in the presence of Friedel-Crafts acids was studied. As expected [M. Spiteller, J. Jovanovic, Fuel 78(1999)1263] there were dimers and trimers in the product mixture together with higher oligomers. Among products with double molecular weight relative to the molecular weight of indene, the structure of four compounds was determined: 6-(2?,3?-dihydro-1?H-inden-1?-yl)-1H-indene 2-(2?,3?-dihydro-1?H-inden-1?-yl)-1H-indene 1-(2?,3?-dihydro-1?H-inden-2?-yl)-1H-indene and 2,3,1?,3?-tetrahydro-[1,2?]biindenylidene. It was shown that the first one represents an indene alkylation product and that the others were obtained by bonding of the indan-1-ylium ion and indene at the position 2, followed by acid catalyzed 1,2-hydride rearrangement in the case of the third and fourth one. Considering the indene dimerization products as components of pyrolysis oils and as interesting compounds to be used as model substances for NMR, MS and X-ray analysis, the reaction, separation and isolation parameters were optimized in this study.