[CH3:1][N:2](C=O)C.[C:6]([C:8](=[CH:11][CH3:12])[C:9]#[N:10])#N.P(Cl)(Cl)(Cl)=[O:14].Cl[CH2:19][Cl:20]>O>[Cl:20][C:19]1[C:12]([C:1]#[N:2])=[CH:11][C:8]([CH:6]=[O:14])=[CH:9][N:10]=1A mixture of 292 g (4 mol) of DMF and 102 g (0.887 mol) of crude, 80% pure, according to GC analysis, (remainder benzene) 2-cyano-but-2-enenitrile is added dropwise with stirring to 614 g (4 mol) of phosphorus oxychloride in the absence of moisture with ice-bath cooling at 20° to 25° C. in the course of 40 minutes. The mixture is then heated in the course of one hour to 95° to 100° C. and kept at this temperature for a further 24 hours. After cooling, the mixture is worked up in accordance with Example 1 (with respective doubling of the amounts of dichloromethane and water specified there). 24.2g (16.4% of theory) of 2-chloro-3-cyano-5-pyridinecarboxaldehyde are obtained as a crystalline product at a GC purity of 95.2%. Melting point 96° C. after recrystallization from cyclohexane.
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