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During 10 min. (4-chloro-benzyl)-[2,2-dimethoxy-1-methyl-eth-(Z)-ylidene]-amine (120 g, 0.496 mol) was added dropwise to polyphosphoric acid (1000 g) at 130 0C. The resulting reaction mixture was heated for 3 h at 140 0C. After cooling below 100 0C the reaction mixture was poured onto ice (1 kg) and neutralized (pH = 7) with a 33 percent aqueous NaOH solution. Care was taken that the temperature did not rise above 35 0C by adding additional ice. The reaction mixture was extracted with dichloromethane (3 x 1 L) and the combined organic layers were dried over Na2SO4, filtered and concentrated at reduced pressure to afford a black oil. The crude product was purified bulb-to-bulb distillation (105 -110 0C, 2 mbar) to afford the title compound as colorless oil which crystallized upon standing (66.7 g, 0.375 mol, 76percent). MS (ES+): 178 (M(C10H835CIN)+H)+.