Separation of alpha- and delta-tocopherols due to an attenuation of hydrogen bonding

A critical need for recovering chemicals from renewable resources is the de velopment of operations to separate structurally similar compounds. We exam ined an adsorption approach to separate natural, antioxidant tocopherols. S pecifically, we studied adsorption from hexane onto an acrylic ester sorben t and observed that alpha -tocopherol adsorbed with a 3- to 4-fold-lower af finity than delta -tocopherol. Separation factors of 3.3 were observed in m ixture studies. Mechanistic information was obtained by IR and H-1 NMR spec troscopy using ethyl propionate (EP) as a small molecule analogue of the so rbent's binding site. These spectroscopic studies indicate that the phenoli c hydroxyl of the tocopherols can undergo intermolecular hydrogen bonding w ith EP. Spectroscopic measurements also indicate that EP hydrogen bonding t o alpha -tocopherol is less favorable than that to delta -tocopherol. The a ttenuation 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.