Oxidative Bromination Of Salicylaldehyde Research Articles

Heterogeneous Catalytic Oxidative Bromination and Oxidation of Thioethers By Vanadium(IV) Oxido Complex of Benzoylacetone and Effect of Solid Supports

Vanadium(IV) oxido complex of 1-Phenyl-1,3-butanedione [VIVO(bzac)2] (1) was prepared, characterized, and heterogenized onto APTMS modified graphene oxide, as well as imidazole modified polystyrene beads. Graphene oxide supported complex GO-APTMS-[VIVO(bzac)2] (2) and polymer anchored complex PS-im-[VIVO(bzac)2] (3) were used for the oxidative bromination of a number of small organic molecules and oxidation of a series of thioethers. Both 2 and 3 evolve as excellent heterogeneous catalysts. The nature of solid support does not impact substrate conversion (%) during the oxidative bromination of salicylaldehyde, phenol, or styrene, whereas it influences the substrate conversion (%) as well as the product selectivity (%) during the oxidation of thioethers.

Synthesis, structural studies and catalytic activity of dioxidomolybdenum(VI) complexes with aroylhydrazones of naphthol-derivative

Reaction of the salicylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L1), anthranylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L2), benzoylhydrazone of 2-hydroxy-1-acetonaphthone (H2L3) and anthranylhydrazone of 2-hydroxy-1-acetonaphthone (H2L4; general abbreviation H2L) with [MoO2(acac)2] afforded a series of 5- and 6- coordinate Mo(VI) complexes of the type [MoO2L1–2(ROH)] [where R=C2H5 (1) and CH3 (2)], and [MoO2L3–4] (3 and 4). The substrate binding capacity of 1 has been demonstrated by the formation of one mononuclear mixed-ligand dioxidomolybdenum complex [MoO2L1(Q)] {where Q=γ-picoline (1a)}. Molecular structure of all the complexes (1, 1a, 2, 3 and 4) is determined by X-ray crystallography, demonstrating the dibasic tridentate behavior of ligands. All the complexes show two irreversible reductive responses within the potential window −0.73 to −1.08V, due to MoVI/MoV and MoV/MoIV processes. Catalytic potential of these complexes was tested for the oxidation of benzoin using 30% aqueous H2O2 as an oxidant in methanol. At least four reaction products, benzoic acid, benzaldehyde-dimethylacetal, methyl benzoate and benzil were obtained with the 95–99% conversion under optimized reaction conditions. Oxidative bromination of salicylaldehyde, a functional mimic of haloperoxidases, in aqueous H2O2/KBr in the presence of HClO4 at room temperature has also been carried out successfully.

Synthesis, characterisation and catalytic potential of oxovanadium(IV) based coordination polymers having a bridging methylene group

Three polymeric oxovanadium(IV) complexes: [ CH 2{VO(salen)} ] n , [ CH 2{VO(sal-1,2-pn)} ] n and [ CH 2{VO(sal-1,3-pn)} ] n of the polymeric Schiff bases derived from 5,5′-methylenebis(salicylaldehyde) [CH 2(Hsal) 2] and 1,2-diaminoethene (en), 1,2-diaminopropane (1,2-pn) or 1,3-diaminopropane (1,3-pn) have been isolated and characterised by various physico-chemical techniques. All these complexes are insoluble in common solvents and are paramagnetic. IR spectral data confirm the coordination of ligands through the azomethine nitrogen and the phenolic oxygen atoms to the metal ion. EPR spectra of these complexes reveal the paramagnetic nature of the complexes, and anisotropic axial patterns and the Hamiltonian parameters predict a square pyramidal geometry around vanadium ions in these complexes. These complexes exhibit good catalytic activity towards the liquid-phase hydroxylation of phenol into a mixture of catechol and hydroquinone using H 2O 2 as an oxidant. Various parameters, such as concentrations of substrate, catalyst and oxidant, as well as reaction time and temperature, have been taken into consideration for the maximum hydroxylation of phenol. Under the optimised conditions, the selectivity values towards the formation of catechol and hydroquinone are about 90–98 and 2–10%, respectively. These complexes also exhibit good catalytic activity towards the oxidative bromination of salicylaldehyde in water in the presence of H 2O 2/KBr to 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde.

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

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.