42849-58-1Relevant academic research and scientific papers
Photochemical reaction mechanisms of 2-nitrobenzyl compounds in solution I. 2-Nitrotoluene: Thermodynamic and kinetic parameters of the aci-nitro tautomer
Schwoerer, Markus,Wirz, Jakob
, p. 1441 - 1458 (2007/10/03)
The largely reversible, light-induced tautomerization of 2-nitrotoluene (1) to the quinonoid aci-nitro tautomer aci-1 was studied by flash photolysis as a benchmark for comparison with the widely used nitrobenzyl phototriggers ('caged compounds'). The pH-rate profile for the decay of aci-1 in aqueous solution exhibits downward curvature at pH 3-4, which is attributed to pre-equilibrium ionization of the nitronic acid aci-1 to its anion 1 (pKa = 3.57). Two regions of upward curvature, at pH ca. 6 and o ≈- 1), each indicate a change in the reaction mechanism. The elementary reactions that dominate between the curved regions are assigned on the basis of kinetic isotope effects and the observation of general acid catalysis: Hydronium ions regenerate 2-nitrotoluene by C-protonation of 1 in the pH range of 0-6, and H2O is the proton source at pH>6. A hird, irreversible Nef-type isomerization of aci-1 prevails in highly acidic solutions (pH0). The equilibrium constant for the thermal tautomerization of 1 to aci-1 is estimated as pKT = 17.0 ± 0.2 based on kinetic data.
