Catalytic efficiency and stability of tertiary amines in oxidation of methyl 4-deoxy-β-L-threo-hex-4-enopyranosiduronic acid by hypochlorous acid

Tertiary amines efficiently catalyze oxidation of unsaturated organic substances by hypochlorous acid (HOCl). However, the quaternary chloroammonium cation, formed spontaneously as the reactive species, often undergoes parallel self-decomposition that increases the catalyst dosage required. Thus, an otherwise potential industrial catalyst, 1,4-diazabicyclo[2.2.2]octane (DABCO), decomposes in a few seconds in the presence of HOCl. In this paper, we show that substituting one of the amino groups of DABCO with an alkyl group, in this case with carboxymethyl group, fully stabilizes the polycyclic chloroammonium cation towards self-decomposition. The catalytic efficiency of N-carboxymethyl-1,4-diazabicyclo[2.2.2]octane was similar to, or only slightly lower than that of DABCO, under mild acid conditions (pH 3-6). Although we studied oxidation of methyl 4-deoxy-β-L-threo-hex-4-enopyranosiduronic acid only, the main conclusions on the effect N-alkylation on the catalyst stability and activity should be transferable to catalytic conversion of any other substrate by HOCl.