A new, "Elongated" oxo ketene intermediate in the dissociative hydrolysis of 2,4-dinitrophenyl (2E,4E)-5-(4'-hydroxyphenyl)pentadienoate

Reactivity comparison, Arrhenius parameters, and trapping of the above-depi cted unsaturated intermediate strongly suggest that the alkaline hydrolysis of the title ester follows a mechanism of the E1cB type. This is the first observation of the occurrence of a dissociative route in the hydrolysis of an acyl derivative with three pi-systems interposed between the hydroxyl g roup (the internal nucleophile upon ionization) and the reaction center. Co mparison with the hydrolysis of 2,4-dinitrophenyl 4'-hydroxybenzoate shows that interposition of the vinylenic groups is beneficial to the dissociativ e route.