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On-line and off-line NMR and LC-NMR identification of carbohydrazide derivatives in the reaction mixtures

Aromatic Schiff bases derived from carbohydrazide possess a broad spectrum of pharmacological activities and a wide variety of applications in many fields, such as inorganic, analytical and organic chemistry. They have been used as multitopic ligands for the targeted construction of bioactive coordination systems, as selective analytical reagents for ion binding and as precursors in the syntheses of nitrogen containing heterocycles. Schiff bases can easily be prepared by the condensation reaction between appropriate primary amine and carbonyl compounds. The condensation of carbohydrazide with salicylaldehyde in different solvents yielded a mixture of mono- (1) and bis(salicylidene)carbohydrazide (2). Structure characterization of the reaction products in solution and solid state was performed by off-line NMR, Raman and SWAXS analysis. It has been demonstrated that the ratio of 1 and 2 and the polymorphic content of 2 are dependent on solvent used for the reaction. In order to precisely estimate the product ratio and reaction end point in real time, the process was also monitored on- line by a coupled LC-NMR system.

carbohydrazide derivatives; synthesis; on-line LC-NMR; off-line NMR

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