The alkaline anthraquinone-2-sulfonate-H2O2-catalyzed oxidative degradation of lactose: an improved Spengler-Pfannenstiel oxidation.

The alkali-catalyzed oxidative degradation of lactose (1) to potassium O-beta-D-galactopyranosyl-(1----3)-D-arabinonate (2) has been studied and compared with that of D-glucose to D-arabinonate and D-galactose to D-lyxonate. A mechanism for the degradation of 1 catalyzed by alkali only is presented and discussed, taking into consideration the main reaction products. Increasing the reaction temperature from 293 to 318 K resulted in a drastic decrease of the selectivity for 2. Increasing the oxygen pressure from 1 to 5 bar did not significantly influence the selectivity. The overall reaction kinetics followed first-order behavior with respect to lactose, D-glucose, or D-galactose. The simultaneous addition of catalytic, equimolar amounts of sodium 2-anthraquinonemonosulfonate and H2O2 showed a pronounced effect on the selectivity. A reaction mechanism for this type of alkali-catalyzed oxidative degradation of carbohydrates is presented and discussed. Lactose could be oxidized up to almost complete conversion with a selectivity of 90-95% (mol/mol), whereas D-glucose was oxidized to D-arabinonate with a selectivity of 98%. This increased selectivity was maintained at temperatures from 293 up to 323 K, allowing a reduction of the batch time necessary for almost complete conversion from 50 to 1.5 h. The overall reaction kinetics still followed first-order behavior with respect to lactose, D-glucose or D-galactose. The apparent activation energy amounted to 114 +/- 2 kJ mol-1 for lactose, to 109 +/- 2 kJ mol-1 for D-glucose, and to 104 +/- 9 kJ mol-1 for D-galactose.

The effect of bismuth on the selective oxidation of lactose on supported palladium catalysts.

The selective oxidation of lactose by molecular oxygen has been studied in a batch reactor containing an aqueous slurry of 0.5 kmol m-1 reactant and 1.0 kg m-3 catalyst. The in situ Bi promotion of a commercial Pd-C catalyst resulted in 100% selectivity to sodium lactobionate up to conversions of 95% in the pH range 7-10 and at temperatures up to 333 K. Performing the reaction under such conditions that the oxygen transfer to the liquid phase was rate-controlling allowed the production of sodium lactobionate in high yields in approximately 1 h. A maximum initial reaction-rate of 0.47 mol kg-1 s-1 was found at a molar Bi to Pd ratio of 0.50-0.67. Fifteen batches of lactose were oxidized with the same charge of catalyst without significant loss in initial activity or selectivity. Such other aldoses as maltose, glucose, and galactose could be oxidized analogously with similar selectivities.

Liquid chromatography of sugars on silica-based stationary phases.

A review is given of sugar analysis by liquid chromatography using silica columns. Aspects covered are column materials and preparation, chemically and physically modified amine columns, octadecyl-and unmodified silica columns; eluent composition and elution mechanisms for the different types of columns used; detection methods, RI and UV detectors, visible light, fluorescence, moving-wire, polarimetric and mass detection; and sample preparation and origin of samples.