Asymmetric Aerobic Oxidation of α‐Hydroxy Acid Derivatives Catalyzed by Reusable,Polystyrene‐Supported Chiral N‐Salicylidene Oxidovanadium tert‐Leucinates

The direct immobilization of two different C‐5‐propargyl ether‐modified, chiral N‐salicylidene vanadyl(V) tert‐leucinates onto 4‐azidomethyl‐substituted polystyrene by click chemistry was examined. Among the eight different solvents investigated, the resulting polystyrene‐supported catalysts promote the asymmetric, aerobic oxidation of α‐hydroxy (thio)esters and amides with enantioselectivities of up to 99% ee (selectivity factor up to 41) in chloroform. These polystyrene‐supported catalysts can be readily recovered by filtration and reused for at least four consecutive runs without discernible loss of reactivity and enantioselectivity.     

Comparison of Starch Extraction from Tapioca Chips,Pellets and Roots

The extraction of starch from tapioca chips and-pellets was studied in comparison to the extraction from tapioca roots especially with regard to the starch yield and -quality as well as to the use of by products on a laboratory scale. It was observed that the extraction of starch from the dried raw materials was more complicated than from fresh roots. Impurities were difficult to remove from chips and pellets, so that mostly mineral substances were found in the starch which reduce its quality. A wet cleaning is possible only with chips, because they have a sufficient mechanical stability.