Aza-Michael reaction with enone-modified vegetable oils: evidence of the keto–enolic equilibrium by NIR chemical imaging and evolving factor analysis

The existence of an enone–dienol tautomerism in enone-containing triglyceride, obtained from high oleic sunflower oil, was detected in an image set captured at 95 °C by fixed-size image window-evolving factor analysis. A ¹H NMR spectrum and a UV–Visible spectrum of the enone-containing triglyceride at 25 °C and at 95 °C were measured to corroborate the presence of the enol form. The presence of this equilibrium explains the different behaviour of the curing reaction between an enone-containing triglyceride and diaminodiphenylmethane, which was evaluated following the spectral evolution of two pixels that differ in the presence or absence of the enol form. As the enol form acts as a inert species in the reaction, it leads to different degree of advance depending on which growing zone is observed.