Nitration of δ-tocopherol (1) with either concentrated nitric acid or with nitrating agents in the presence of oxidants provides
5-(7’-nitro-δ-tocopher-5’-yl)-7-nitro-δ-tocopherol [bis(7-nitro-δ-tocopheryl), 6]. Under non-oxidative conditions, the 5-nitro and 5,7-
dinitro products of δ-tocopherol are formed without production of 6. The dimer 6 is C2-symmetric and shows unrestricted rotation around
the 5-5’ bond and a strong hydrogen bond from the phenolic hydroxyl to the neighboring nitro group in both halves of the molecule. The
crystal structure of the side chain-truncated model compound 6a contains crystallographically C2-symmetric molecules with two intramolecular
O-H···O(nitro) hydrogen bonds.
Keywords: Antioxidants, nitration, nitric acid, oxidation, oxidative dimerization, phenols, δ-tocopherol, tocopherols, vitamin E
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