ASCORBATE - ANTIOXIDANT ACTIVITY DETERMINED IN A HYDROCARBON PHASE USING QUATERNARY AMMONIUM-SALTS AS PHASE-TRANSFER AGENTS

By shaking sodium ascorbate with tetra-n-butyl ammonium bromide in a two-phase system consisting of water and organic phases, such as 1,1,2,2-tetrachloroethane (TCE) or chlorobenzene, sufficient concentrations of the quaternary ammonium-ascorbate (quat-ascorbate) are transferred into the organic phase to be useful for antioxidant studies in nonpolar solvents. The antioxidant activity of the quat-ascorbate was determined by measurement of the (inhibition) rate constant, k(inh), for the inhibition of autoxidation of styrene initiated thermally by azobisisobutyrylnitrile (AIBN) at 30-degrees-C. The k(inh) of ascorbate in styrene, found to be (9.63 +/- 2.0) x 10(4) M-1 s-1, is very much lower than that found for ascorbyl-6-palmitate, k(inh) = (110 +/- 11) x 10(4) M-1 s-1 under these conditions. The differences are discussed in terms of the relative effectiveness of hydrogen-atom transfer from the enolic hydroxyl at position 2 of the ascorbate ion compared with the more facile such transfer from position 3 of ascorbyl 6-palmitate in a nonpolar medium.