From native starch to hydrophilic and hydrophobic products:: a catalytic approach

Two new catalytic processes have been developed to modify the hydrophilic/hydrophobic properties of insoluble, native starch. Soluble metal catalysts under proper reaction conditions were used to prepare tailor-made products suitable for various technological applications. Selective, clean oxidation of native starch by hydrogen peroxide in the presence of 0.003-0.016 mol% of iron tetrasulfonatophthalocyanine catalyst (FePcS) provided hydrophilic starch having 0.5-7 carboxyl and 1-11 carbonyl functions per 100 AGU (anhydroglucose units). The oxidation reaction was performed either with starch suspended in catalyst solution or by impregnation of starch powder with catalyst solution (dry process). Only small amounts of water, hydrogen peroxide and cheap FePcS catalysts were needed in the dry process to achieve a successful modification of starch in one step with almost quantitative yields. Hydrophobic starches with degree of substitution ranging from 0.08 to 0.43 per AGU have been prepared by butadiene telomerization in the presence of soluble palladium complexes. The best results in terms of degree of substitution at 50degreesC have been obtained with Pd/TPPTS catalyst. The telomerization of starch with isoprene was also demonstrated. The etherified starch can be further transformed by hydrogenation using Wilkinson-type catalyst in EtOH=H2O.