The Selective OH Radical Oxidation of Sorbitylfurfural:  A Combined Experimental and Theoretical Study

Abstract

Sorbitylfurfural (Furalglucitol), widely used in the cosmetic industry as antioxidant and antiinflammatory agent, reacts with hydroxyl radical in neutral aqueous solution with a rate constant almost at the diffusional limit, k 1 = 7.3 × 109 M-1 s-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 (k 2 = 1.7 × 106 s-1) in β 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 × 105 s-1) then precedes a disproportionation reaction which leads to the final products (k4 = 2.0 × 107 M-1 s-1). The proposed mechanism is based on the UV−vis spectra of intermediates and final products obtained after pulse and gamma radiolysis, on nonlinear 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.

2,4-Furfurylidene-D-sorbitol and its tetra-methyl ether: synthesis, conformational studies, and radical scavenging activity

“…11 Our data confirm that compound 1 has a higher scavenging activity than D-sorbitol 3 alone and show that a cyclic furan acetal is more active than a non-cyclic furan acetal like 5. Therefore the scavenging activity of compounds 1 and 2 is apparently due to a synergic interaction of the D-sorbitol backbone with a conformationally locked acetal structure where the furan ring occupies a stable equatorial position.…”

A kinetic, spectral and theoretical investigation on the role of oxygen in the radiolytic oxidation of a sorbityl cyclic acetal

“…The reaction of OH with SF and with furfural, one of its components, was clarified in our recent papers [1,7], in connection with the effect of controlled amounts of oxygen added to produce peroxyl species [6]. Peroxyl radicals were proven to decay undergoing both an intra-and inter-molecular rearrangement.…”

“…In order to verify the reliability of this combination of theoretical tools, the spectrum of SF itself was first obtained [1], and the agreement found when comparing it with the experimental one gave an indication that the method could indeed be trusted for further applications with similar molecules [26].…”

“…As indicated by the coincidence of the spectra between 27.5 μs and 15 ms in the 230-260 nm zone, this species appears to be long living. The band at 295 nm, known to be related to the formation of one of the transients deriving from the O 2 addition to SFOH [1], was completely bleached after a few hundreds of μs. This evidences that at 27.5 μs there are two different species absorbing at 295 and 235 nm.…”

“…The peculiarity of sorbitylfurfural (1-(2-furan-2-yl-5-hydroxy-6-hydroxymethyl- [1,3]dioxan-4-yl)-ethan-1,2-diol, SF (Scheme 1)), a cyclic acetal deriving from the condensation of D-sorbitol and furfural, when attacked by oxidizing radicals [1,2], consists in exhibiting a unique reactive site, i.e., the carbon in position 5 of the furanic ring. Any other reaction path involving the sugar carbons or other site of the furanic ring, seems to be inhibited when furfural is condensed to a carbohydrate.…”