Bromination of Tocopherols: Oxidative Halogenations and Rearrangements

Abstract

The bromination behaviour of all four tocopherols and the corresponding model compounds in acidic and basic aqueous media was studied. Acidic conditions resulted in quinones and brominated quinones, with the bromination of the tocopherol preceeding the oxidation to the quinone. Buffer type and concentration did not influence the reaction results, whereas pH and the ratio of buffer and ethanol used as a cosolvent strongly affected the reaction rates. In alkaline media, two or three major products and a multitude of minor byproducts were obtained, because the combination of oxidizing hypobromite and alkaline conditions allowed for more complex reaction pathways (oxidation, substitution, conden-

Regenerable Antioxidants—Introduction of Chalcogen Substituents into Tocopherols

“…[17] Except for the permethylated a-tocopherol, compounds 2-4 are known to undergo aromatic electrophilic substitution. In this way, bromo-, [18] nitro-, [19] nitroso-, [20] mercury- [20] and aminomethyl groups [21] were introduced into the non-a-tocopherols. To the best of our knowledge, chalcogen substituents were not previously introduced in this way into the tocopherol scaffold.…”

A Green Protocol for the Bromination and Iodination of the Aromatic Compounds using H5IO6/NaBr and H5IO6/NaI in the Water

“…Recently, the oxidative halogenation of organic compounds by halides have emerged as an important alternative for the synthesis of such haloderivatives. [19][20][21][22][23][24][25][26][27][28][29][30] Despite the broad choice of options, however, many bromination and iodination methodologies are cumbersome, costly and harsh or involve the use of toxic heavy metals, volatile organic solvents, or elemental halogenes which are highly corrosive, toxic or self-sublimating. In addition, there are some environmental hazards with respect to handling them.…”

Dynamical regime of resorcinol based Belousov–Zhabotinsky chemical oscillator in the presence or absence of some hydrophobic antioxidants in aqueous–organic mixed media

“…Bohmdorfer, et al found that in case of a-tocopherol, halogenating effect is minor and the major pathway is the oxidative action resulting in the para-quinone. 52 Hence, the bromination is mainly observed by the resorcinol instead of a-tocopherol. Further, it is observed that increasing the concentration of TFMBA up to 0.005 mol L À1 and for b-carotene up to 0.0005 mol L À1 completely quenches the oscillations.…”