[OH:1][C:2]1[C:9]([OH:10])=[CH:8][CH:7]=[CH:6][C:3]=1[CH:4]=[O:5].[C:11](=O)([O-])[O-].[K+].[K+].C(Cl)Cl>[Cu]=O.CN(C)C=O>[CH2:11]1[O:10][C:9]2[C:2](=[C:3]([CH:6]=[CH:7][CH:8]=2)[CH:4]=[O:5])[O:1]1138.0 g (1.0 mol) of 2,3-dihydroxybenzaldehyde, 415.0 g (3.0 mol) of potassium carbonate, 4.7 g of copper oxide, 255.0 g (3.0 mol) of methylene chloride and 1500 ml of distilled dimethylformamide are boiled for 7 hours, while stirring intensively.. The reaction mixture is evaporated to dryness in vacuo and, after addition of 1000 ml of ice-water to the residue, the mixture is extracted four times by shaking with 300 ml of methyl tert-butyl ether each time. The combined ether extracts are washed with 5% strength sodium hydroxide solution and water and dried over sodium sulphate. The methyl tert-butyl ether is then stripped off (and can be reused) and the residue is distilled in vacuo at 92°-93° C./1 mbar. 120 g (80% of theory) of 2,3-methylenedioxybenzaldehyde having a melting point of 32°-33° C. are obtained.
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