[CH3:1][C:2]1[C:9]([N+:10]([O-:12])=[O:11])=[CH:8][C:7]([CH3:13])=[CH:6][C:3]=1[CH2:4]Cl.C(O)(=[O:16])C.C1N2CN3CN(C2)CN1C3.Cl>O>[CH3:1][C:2]1[C:9]([N+:10]([O-:12])=[O:11])=[CH:8][C:7]([CH3:13])=[CH:6][C:3]=1[CH:4]=[O:16]The mixture constituted by 2,5-dimethyl-3-nitrobenzyl-chloride (A) prepared according to M. J. Winchester and F. D. Popp, J. Het. Chem. 12, p. 547 (1975) (610 g), acetic acid (1280 ml, water (1280 ml) and hexamethylene tetramine (855 g) was heated with reflux under stirring for 2 hours. 1037 ml of concentrated hydrochloric acid were then added in 10 minutes and the mixture was again heated with reflux for 20 minutes. This mixture, cooled to 0° C., gave a solid which was filtered off, dried and recrystallised from cyclohexane (4 liters) to give 290.5 g (53%) of yellow needles corresponding to the aldehyde of formula B, melting point: =90°-93° C.
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