N[C:2]1[S:3][C:4]2[CH:10]=[CH:9][CH:8]=[CH:7][C:5]=2[N:6]=1.[OH-:11].[Na+].[Na].[K].S[C:16]1[CH:21]=CC=C[C:17]=1NC(N)=O>C(O)(=O)C.C=C1OC(=O)C1.O>[CH2:17]([C:2]1[S:3][C:4]2[CH:10]=[CH:9][CH:8]=[CH:7][C:5]=2[N:6]=1)[C:16]([CH3:21])=[O:11]The water-moist 2-mercaptophenylurea obtained according to European Pat. No. 0,039,483, Example 1, paragraph 1, by reacting 150 parts of 2-aminobenzothiazole with 150 parts of sodium hydroxide and working up the mixture with water, or an appropriate amount of the sodium or potassium salt of the said 2-mercaptophenylurea, is dissolved in 500 parts of 50% strength acetic acid, and 118 parts of diketene are then added dropwise in the course of 2 hours at 45° to 50° C. Stirring is continued for 1 hour, after which the mixture is heated to the reflux temperature and kept at a temperature of 95° C.-100° C. for 2 hours. It is then cooled to room temperature, and the precipitated 2-acetonylbenzothiazole of the formula ##STR13## is isolated by filtration and dried in vacuo at 60° C.-80° C. 151.7 parts of a product of melting point 118° C.-119° C. are obtained; this corresponds to a yield of 79.4%, based on 2-aminobenzothiazole employed.
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