[NH2:1][C:2]1[CH:11]=[CH:10][C:5]2=[N:6][C:7](=[O:9])[N:8]=[C:4]2[CH:3]=1.[CH2:12]=[C:13]1[O:17][C:15](=[O:16])[CH2:14]1.C(C1C=CC2=NC(=O)N=C2C=1N)(=O)CC(C)=O>O>[C:15]([NH:1][C:2]1[CH:11]=[CH:10][C:5]2=[N:6][C:7](=[O:9])[N:8]=[C:4]2[CH:3]=1)(=[O:16])[CH2:14][C:13]([CH3:12])=[O:17]Via the bottom inlet tube of a glass vessel having a capacity of 80 liters, a clarified solution of 150 kg of 5-aminobenzimidazolone in 4200 l of water, which solution has a temperature of 90° C., is fed in at a rate of 2100 l/h with agitation. Simultaneously, via a cover inlet tube, diketene is added at a rate of 50 l/h. Immediately, a colorless precipitate of 5-acetoacetyl-aminobenzimidazolone forms. The suspension thus obtained flows via a lateral tube which limits the reaction volume to 40 l into a 8 m3 agitation vessel of stainless steel containing already 1000 l of water having a temperature of 80° C. The reaction temperature in the glass vessel is maintained at 80°-85° C. by spraying water having a temperature of 5° C. onto the surface of the suspension by means of a spray ring (amount of water about 500-600 l/h). After the reaction is complete, the reaction mixture is cooled to 40° C., and the 5-acetoacetylaminobenzimidazolone is isolated by means of a suitable filter. 550 kg of a reaction product of about 40% strength are thus obtained which may be directly used for pigment synthesis without a further purification step.
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