Condensation Reaction between Carbohydrazide and Salicylaldehyde: in-line Vibrational Spectroscopy Monitoring and Characterization of the Reaction Products in Solution and Solid State

The condensation reaction between carbohydrazide and salicylaldehyde was monitored in-line by using vibrational NIR
and Raman spectroscopies and statistical methods. Prior to in-line data analysis the reaction products were fully charac-
terized in solution and solid state in order to check the potential of the in-line approach as a tool for in-process Schiff ba-
ses reaction control. It was demonstrated that a combination of vibrational spectroscopy and principal component analy-
sis made it possible to detect and identify the reaction products, e.g. mono(salicylidene)carbohydrazide (1) and bis(sa-
licylidene)carbohydrazide (2) in different solvents, and to determine the reaction end points in real time. Owing to com-
plexity of the reaction mixtures and band overlapping, it was not possible to determine the relative ratio of the reaction
products in-line. The off-line analysis showed that 1 was predominant in methanol while the highest portion of 2 was ob-
tained in ethano