Regioselective oxidation of primary hydroxyl groups of sugar and its derivatives using a new catalytic system mediaed by TEMPO

摘要

Primary hydroxyl groups were oxidized regioselectively using roganic oxoammonium salts generated on supported silver catalysts. which promote disproportionation of 2,2, 6,6-tetramethylphiperidinyl-1-oxy (TEMPO) in aqueous solution. The oxidation reactions were performed at pH 9.5 in a batch reactor at RT using heterogeneous silver catalysts and peroxides as primary co-oxidants. 99 mol. percent selectivity to methyl-alpha-D-glucopyrasiduronic acid was obtaiend at 90 percent conversion of the pyranoside over a silver-celite catalyst. The activity was increased by adding carbonates to the silver catalysts. This results can be explained by the increase of the electron charge defiicency on silver in presence of carbonate, which accelerates the nucleophilic attack of TEMPO and/or hydroxyl groups. This result was proved using TPD of ammonia in the case of Ag-Al_2O_3 catalyst. The observed regioselectivity is due to the sterical hindrance caused by the four methyl groups in TEMPO.