Dicarboxylic acid monohydrazides

Hydrazinolysis of dimethyl pyridine-3,4-dicarboxylate gives the hydrazinium salt of a pyridine-3,4-dicarboxylic acid monohydrazide, thought to be the 4-carboxylic acid 1. The hydrazinium salt or free acid, respectively, on heating at 365-370°C cyclizes to give pyrido[3,4-t/]-pyridazine-1,4-(2//,3//)-dione (2).117... 

The hydrazinium salt of pyridine-3,4-dicarboxylic acid monohydrazide or the free acid 1 was heated at 365 -370 °C, at which temperature the melt started to decompose and yielded a nearly colorless sublimable product. The compound was purified by recrystallization (HOAc), or by dissolving it in NH4OH, followed by filtration and precipitation with HOAc to give yellowish or colorless needles mp 365°C. 

Of course, the DNP-derivatives of the dicarboxylic acid monohydrazides also remain in the aqueous layer. 

Dicarboxylic acid monohydrazides from dicarboxylic acid anhydrides... 

Derivatization of acids with 2-nitrophenylhydrazine has been described in a number of publications [111-115]. N,N -Dicyclohexylcarbodiimide (DCCI) [111] or 1-ethyl-3-(dimethylaminopropyl)carbodiimide (EDCi) (114,115) was used for the activation of the carboxylic acid function. Normally the derivatives were detected at 550 nm. Miwa and Yamamoto [115] applied this method to the determination of urinary dicarboxylic acids, which reacted with 2-nitrophenylhydrazine to form monohydrazides. The adds were extracted from acidified urine with ethyl acetate and dried. After derivatization, the monohydrazides of the dicarboxylic acids were first separated from the hydrazides of monocarboxylic acids and other interfering substances by a two-step extraction. The recoveries varied from 27.6-103.1%, depending on the polarity and the water solubility of the acids. The separation of monohydrazides of 11 straight- and branched-chain dicarboxylic acids was performed on an ODS column at 40 °C by isocratic elution with acetonitrile-phosphate buffer containing counter-ions such as tetramethylammonium as mobile phase. Detection was at 400 nm. 

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