The selective OH radical oxidation of Sorbitylfurfural: a Combined Experimental and Theoretical Study

Sorbitylfurfural (Furalglucitol), widely used in cosmetic industry as antioxidant and anti-inflammatory agent, reacts with hydroxyl radical in neutral aqueous solution with a rate constant almost at the diffusional limit, k1 = 7.1 x 10^9 M-1s-1. Despite the unselective character of the OH radical, addition to the 5? position in the furanic ring seems to provide the dominant path. The consequent allylic radical undergoes the cleavage of the C-O bond (k2 = 1.7 x 10^6 s-1) in beta position to form a pseudo- seven-atom ring via a hydrogen bond between the attacking OH group and the furanic oxygen. A 1,6 H-shift between the two oxygen atoms (k3 = 1.4 x 10^5 s-1) then precedes a disproportionation reaction which leads to the final products (k4 = 2.0 x 10^7 M-1s-1). The proposed mechanism is based on the UV-vis spectra of intermediates and final products obtained after pulse and gamma radiolysis, on non-linear kinetic fittings of absorbance versus time curves, on quantum-mechanical calculations of electronic transitions and reaction enthalpies. The two most important final products have been isolated and characterized as sorbityl-but-2-enal derivatives by LC-MS.