Separation of α- and δ-tocopherols due to an attenuation of hydrogen bonding

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 alpha -tocopherol adsorbed with a 3- to 4-fold-lower affinity than delta -tocopherol. Separation factors of 3.3 were observed in mixture studies. Mechanistic information was obtained by IR and H-1 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 alpha -tocopherol is less favorable than that to delta -tocopherol. The attenuation of alpha -tocopherol's hydrogen bonding is likely due to steric constraints imposed by the methyl substituents ortho to alpha -tocopherol's phenolic hydroxyl group.