RESUMO
Starch can be efficiently converted into the corresponding formates homogeneously using N-formyl imidazole obtained by the reaction of 1,1'-carbonyldiimidazole and formic acid in dimethyl sulfoxide as a solvent. Starch formates are soluble in polar aprotic solvents, not susceptible against hydrolysis, and not meltable. Thermoplastics could be generated by conversion of starch formates with long-chain fatty acids exemplified by the conversion with lauroyl chloride in N,N-dimethylacetamide, leading to mixed starch laurate formates. The mixed esters show melting temperatures mainly dependent on the amount of laurate ester moieties.
RESUMO
Maize starch was allowed to react homogeneously in N,N-dimethylacetamide (DMAc)/LiCl with lauric acid activated with 4-toluenesulfonyl chloride, N,N'-dicyclohexylcarbodiimide/4-(1-pyrrolidinyl)pyridine, 1,1'-carbonyldiimidazole, and N,N-dimethylformamide (DMF) combined with oxalyl chloride. Characterization of the products by means of 13C NMR spectroscopy revealed different substitution patterns depending on the activation agent. The activation of lauric acid with DMF in combination with oxalyl chloride gave starch laurates of highest degree of substitution (DS), yield and reaction efficiency. The melting temperatures and the solubility of the thermoplastic starch laurates were found to depend on the DS, the substitution pattern, and on the molar mass of the starch esters.
