PHOTOLYSIS OF D-FRUCTOSE IN AQUEOUS SOLUTION

Article abstract of DOI:10.1016/S0008-6215(00)81031-9

In the 254-nm photolysis of aqueous solutions of D-fructose, only the open-chain form, which is present to an extent of ca. 0.8percent in equilibrium with the cyclic forms, absorbs the light.A study of the products and their quantum yields reveals that the main, primary process is C-C bond cleavage α to the carbonyl group.In the absence of oxygen, the subsequent reactions of the resulting radicals are (a) loss of CO from the hydroxyalkylacyl radicals (estimated rate constant k ca. 3*1E6 s^-1); (b) consecutive elimination of two molecules of water from the tetritol radicals; and (c) disproportionation and combination reactions.A peculiar product is trans-4-hydroxy-2-butenal, whose precursor is formed from the tetritol radical through elimination of two molecules of water.This compound is a good radical-scavenger and during photolysis quickly attains a low steady-state concentration.One of the products derived from it is a 2,3-dideoxy-2,3-di-C-hydroxymethyltetrose.In the presence of oxygen, the CO elimination process is partly, and the water elimination reactions are fully, suppressed by the fast addition of oxygen to the acylalkyl and hydroxyalkyl radicals.The peroxyl radicals react through unimolecular elimination of HO2^. from α-hydroxyalkylperoxyl radicals and bimolecular dismutation with loss of O2, accompanied by loss of CO2 when hydroxyalkylacylperoxyl radicals are involved.