[OH-].[K+].[O:3]1[C:7]2[CH:8]=[CH:9][CH:10]=[CH:11][C:6]=2[C:5](=[O:12])[CH:4]1C(OC)=O.O1C2C=CC=CC=2C(=O)C1C(OCC)=O.Cl>O.C(O)C>[O:3]1[C:7]2[CH:8]=[CH:9][CH:10]=[CH:11][C:6]=2[C:5](=[O:12])[CH2:4]1A solution is prepared from 8.2 l of water and 8262 g (125.4 mol) of potassium hydroxide (85% pure), 12.5 l of ethanol are added at 50-60° C. and 9079 g of the water-moist mixture, obtained in the 1st stage described above, of methyl benzofuran-3-one-2-carboxylate and ethyl benzofuran-3-one-2-carboxylate (24.79 mol in total) are then added. The mixture is heated under reflux for 45 minutes and 7.3 l of water are then added. This solution is cooled to 20° C. and introduced into a mixture, heated at 55° C., of 17.5 l of concentrated hydrochloric acid and 20 l water in the course of 60 minutes, vigorous evolution of gas taking place. Residues of the alkaline solution are rinsed out with 3 l of water and also introduced into the hydrochloric acid. The mixture is stirred at 60° C. for a further 30 minutes (end of the evolution of gas) and cooled to 20° C. The product is filtered off with suction, rinsed with 6 l of water and dried at 35° c. in a vacuum drying cabinet. 3250 g (94% of theory) of benzofuran-3-one are obtained. HPLC: logP=1.26.
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