Oxidative bromination of salicylaldehyde by potassium bromide/H 2O 2 catalysed by dioxovanadium(V) complexes encapsulated in zeolite–Y: a functional model of haloperoxidases

Abstract

Interaction of ammonium salt of N-isonicotinamidosalicylaldimine (H 2sal-inh) and N-(2-hydroxyphenyl)salicylideneamine (H 2sal-oap) with NH 4VO 3 inserted in Na–Y zeolite in aqueous solution at pH ca. 7.5 leads to the formation of dioxovanadium(V) complexes in the super cages of the zeolite–Y. These encapsulated complexes exhibit good catalytic activity towards the oxidative bromination of salicylaldehyde using H 2O 2 as an oxidant in presence of KBr; a reaction similar to that exhibited by vanadate-dependent haloperoxidases (V-HalPO). Under the reaction conditions the percent formation of a major product 5-bromosalicylaldehyde follows the order: NH 4[VO 2(sal-inh)]–Y (34%) > NH 4[VO 2(sal-oap)]–Y (26.8%) > Na/NH 4VO 3–Y (22%) with ca. 87% selectivity after 4 h of reaction time. These encapsulated complexes do not leach or decompose during catalytic activity study, showing their practical utility over free complexes.