Ethylation of arabinoxylan from Ispaghula (Plantago ovata) seed husk

Abstract

The ethylation of arabinoxylan, isolated from Ispaghula seed husk by alkali extraction, was carried out heterogeneously with ethyl iodide in the presence of aqueous sodium hydroxide (25%). The reaction parameters were varied in terms of molar ratio anhydrosugar unit:reagent, slurry medium, and temperature. In order to determine the total degree of substitution of ethyl groups (DSEt), 1H NMR spectroscopic investigations of ethyl arabinoxylans (EAX) after peracetylation with acetyl chloride in N,N-dimethyl formamide were carried out. Structural elucidation of the peracetylated EAX was conducted by means of 1H, 1H COSY- and HSQC-DEPT NMR experiments. DS values for EAX as high as 0.61 were achieved. Samples were soluble in dimethyl sulfoxide at 80 C. The intrinsic viscosity [g] of EAX samples depends on reaction conditions applied. The highest [g] obtained was 518 mL/g for a sample synthesized at 40 C in methanol as slurry medium using a molar ratio arabinoxylan:ethyl iodide of 1:18.