90350-91-7Relevant articles and documents
Oxidation of Hydroxymalonic Acid by OH Radicals in the Presence and in the Absence of Molecular Oxygen. A Pulse-Radiolysis and Product Study
Schuchmann, Man Nien,Schuchmann, Heinz-Peter,Sonntag, Clemens von
, p. 9122 - 9129 (1995)
The rate constants of the reaction of OH radical/O- radical with hydroxymalonic acid (1) have been determined at various pH, the OH radical being generated pulse-radiolytically.This reaction involves the abstraction of an H atom at C(2), i.e., the formation of the α-hydroxyalkyl radical (2), and is fastest in the pH range from 6 to 10 (k = 4.4E8 dm3 mol-1 s-1) where hydroxymalonic acid exists as the dianion.The pKa values of the carboxyl functions of radical 2 have been found to be 1.9 and 4.8, similar to, or slightly higher than, those of the parent compound (1.89 and 4.28 at 25 deg C).However, the pKa of the alcohol function of radical 2 (found to be 12.9) is several units lower than that of the parent compound.In the presence of oxygen radical 2 is rapidly converted into the corresponding peroxyl radical 3 (k = 1.6E9 dm3 mol-1 s-1).The α-hydroxyperoxy radical (3) eliminates HO2 radical with a rate constant of 1.1E4 s-1 to give ketomalonic acid.In the alkoxide form, peroxyl radical 3 eliminates O2- radical faster (8.9E4 s-1).The pKa of the alcohol function in 3 has been estimated at 9.8, much lower than that of radical 2.In the γ-radiolysis of hydroxymalonic acid in N2O/O2-saturated solutions, product ratios change with pH.At pH 3, the main products (4:1 v/v) are ketomalonic acid (G = 5.1E-7 mol J-1) and hydrogen peroxide.At pH 10 oxalic monoperacid and carbon dioxide become major products.These products are formed in a (slow) chain reaction involving ketomalonic acid and the superoxide radical.Ketomalonic acid also reacts with the product hydrogen peroxide (k = 5E-3 dm3 mol-1 s-1), yielding peroxides which, depending on pH, can be present in different states of protonation.
