General procedure for the synthesis of 2-indenecarboxylic acid from 2,3-dihydro-1H-indene-2-carbonitrile: A mixture of 2,3-dihydro-1H-indene-2-carbonitrile (128) (55.1 g, 0.385 mol), concentrated hydrochloric acid (100 mL), and dioxane (500 mL) was stirred for 41 hours at 60-70°C. Upon completion of the reaction, the mixture was cooled and the dioxane was removed by evaporation to give a residue. The residue was suspended in 1 M hydrochloric acid (300 mL) and stirred at 20 °C for 15 hours. Subsequently, the solid product was collected by filtration, washed with water and dried to give 2-indenecarboxylic acid (129) (54.1 g, 87% yield) as a white solid. Melting point (EtOAc/petroleum ether recrystallization) 128 °C [literature value (Baeyer, A. Perkin W.H., Chem. Ber. 1884, 17, 122) mp 130.2 °C]; 1H NMR (δ): 10.50 (broad single peak, 1H, COOH), 7.14-7.25 (multiple peaks, 4H, H-4, H-5, H -6, H-7), 3.21-3.43 (multiple peaks, 5H, H-1, H-2, H-3).
