Keywords: aromatic acid halides, hydrazide, hydrazine hydrate, hydrazinolysis, X-ray analysis.The studies [1,2] demonstrated the possibility of a stepwise hydrazinolysis of the ester groups in diethyl 2,6-dimethyl-3,5-pyridinedicarboxylate with subsequent formation of 3-ethoxycarbonyl-2,6-dimethyl-5-pyridine-carboxylic acid hydrazide (1) and 2,6-dimethyl-3,5-dipyridinedicarboxylic acid dihydrazide (2) and then the corresponding hydrazones using aromatic aldehydes. It was found that the free ester group in the case of the hydrazones obtained from the monohydrazide 1 does not participate in the hydrazinolysis reaction.With the aim of investigating the chemical properties of the hydrazides 1 and 2 we have studied their acylation reaction with the aromatic acid halides 3a-h. This reaction occurs under base catalysis conditions using dry, refluxing acetonitrile. The choice of solvent and the temperature conditions are limited by the solubility of the hydrazides 1, 2 in organic solvents.The 3,5-pyridinedicarboxylic acid N-aroyl hydrazides 4, 5a-h formed in the reaction are neutralized using aqueous alcoholic sodium bicarbonate solution to give the corresponding bases 6, 7a-h (Tables 1-3). As is evident from the Table the most difficulty occurs in the reaction with 2-methoxybenzoyl chloride and this is evidently linked both with the lower electrophilicity of the reagent and with the steric hindrance generated by the ortho-methoxy group.The N-aroyl hydrazides 6, 7a-h are quite stable to acid and base hydrolysis but this occurs to give 2,6-dimethyl-3,5-pyridinedicarboxylic acid by refluxing for 6-10 h in 15% hydrochloric acid, virtually the same time being needed for the complete hydrolysis using a 2N aqueous alcohol solution of potassium hydroxide under reflux.The ester group of the monohydrazide 1 readily takes part in a hydrazinolysis reaction to give the dihydrazide 2 [1]. We were interested in the possible hydrazinolysis of the ester group in the obtained N-aroyl hydrazides 6a-h. It was found that prolonged reflux of both the bases 6a,b,e,f,h and the hydrochlorides __________________________________________________________________________________________