Mechanistic Studies on the Reaction of o-phthalaldehyde (OPTA) with Urea and its N-alkyl/aryl Derivatives

Urea and its N-alkyl/aryl derivatives react with o-phthalaldehyde (OPTA) to yield blue to purple coloration along-with isoindoline compounds (VII a,b,c) in acidic media. The color is unstable and changes into various shades with the passage of the time. The assay of urea which entirely depends upon this color does not suggest its determination with OPTA present in biological and non-biological fluids. Moreover, it is found that compounds which enhance color stability have nothing to do with determination of urea. The structures of isoindolines (VII a,b,c) have been confirmed by 1H-, 13C-NMR and mass spectrometry techniques. The absolute authenticity comes from their (VII a,b,c) X-ray crystallography.  The colors resulting from the said reactions fall in between 585-595 nm in UV/VIS spectra. As the use of OPTA for urea determination is known, hence, in this study, we are presenting chemistry for urea determination with OPTA.

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