Rapid Halogen Substitution and Dibenzodioxin Formation during Tyrosinase-Catalyzed Oxidation of 4-Halocatechols

Abstract

4-Fluoro-1,2-benzoquinone, generated by tyrosinase oxidation of 4-fluorocatechol in aqueous buffer, rapidly undergoes substitution by O-nucleophiles (water or catechols) with release of fluoride. 4-Chloro- and 4-bromocatechol behave similarly. The reactions, which have toxicological implications, have been monitored by spectrophotometry and HPLC/MS, and intermediate and final products, including dibenzodioxins, identified.

Synthesis of 1‐Arylnaphthalenes by Gold‐Catalyzed One‐Pot Sequential Epoxide to Carbonyl Rearrangement and Cyclization with Arylalkynes

“…Several recent papers reported on the reactions of tetrachlorocatechol with copper17,18 and vanadium19 complexes, where the C 6 Cl 4 (OH) 2 is turned into a chloroanilate ligand. Also, related processes involving the oxidation of hydroquinone and the displacement of fluoride by water have been reported previously 20. These processes of oxidative dehalogenation utilize atmospheric oxygen as an oxidizing reagent and water as a nucleophile displacing the halide.…”

Dopamine‐Based Coatings and Hydrogels: Toward Substitution‐Related Structure–Property Relationships

“…[ 37,38 ] Halide release followed by rapid nucleophilic substitution leading to dimerization and the formation of dibenzodioxin species have been recently reported. [ 39 ] Finally, inclusion of a beta-OH group on the dopamine system, as in the norepinephrine series, results in a greater homogeneity, yet lower thickness, [ 20 ] of the polymeric coating. Oxidative breakdown of the catecholamine chain at the beta reactive site is the main determinant of this difference, [ 40 ] which is likely to account for a lower crosslinking capability of the oxidized monomer and the formation of small benzaldehyde fragments increasing fi lm smoothness via copolymerization and Schiff base formation.…”

Double Oxidative Dehalogenation of 2,5‐Bis(diisopropylphosphoryl)‐3,6‐difluoro‐1,4‐hydroquinone leading to Formation of New Copper Quinonoid Complexes

“…Also, related processes involving the oxidation of hydroquinone and the displacement of fluoride by water have been reported previously. [20] These processes of oxidative dehalogenation utilize atmospheric oxygen as an oxidizing reagent and water as a nucleophile displacing the halide. An analogous mechanism is thought to operate in our systems, since reactions leading towards formation of 2 and 3 were significantly accelerated when water was deliberately added to the reaction mixture.…”