Abstract

A critical need for recovering chemicals from renewable resources is the development of operations to separate structurally similar compounds. We examined an adsorption approach to separate natural antioxidant tocopherols. Specifically, we studied adsorption from hexane onto an acrylic ester sorbent and observed that α-tocopherol adsorbed with a 3- to 4-fold-lower affinity than δ-tocopherol. Separation factors of 3.3 were observed in mixture studies. Mechanistic information was obtained by IR and 1H NMR spectroscopy using ethyl propionate (EP) as a small molecule analogue of the sorbent's binding site. These spectroscopic studies indicate that the phenolic hydroxyl of the tocopherols can undergo intermolecular hydrogen bonding with EP. Spectroscopic measurements also indicate that EP hydrogen bonding to α-tocopherol is less favorable than that to δ-tocopherol. The attenuation of α-tocopherol's hydrogen bonding is likely due to steric constraints imposed by the methyl substituents ortho to α-tocopherol's phenolic hydroxyl group.

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