title: Reactions at interfaces: oxygenation of n-butyl ligands anchored on silica surfaces with methyl(trifluoromethyl)dioxirane.
abstract: The oxygenation of n-butyl and n-butoxy chains bonded to silica with methyl(trifluoromethyl)dioxirane (1) revealed the ability of the silica matrix to release electron density toward the reacting C(2)-H σ-bond through the Si-C(1) and Si-O(1) σ-bonds connecting the alkyl chain to the surface (silicon β-effect). The silica surface impedes neither the alkyl chain adopting the conformation required for the silicon β-effect nor dioxirane 1 approaching the reactive C(2) methylene group. Reaction regioselectivity is insensitive to changes in the solvation of the reacting system, the location of organic ligands on the silica surface, and the H-bonding character of the silica surface. Reaction rates are faster for those organic ligands either within the silica pores or bonded to hydrophilic silica surfaces, which evidence the enhanced molecular dynamics of confined dioxirane 1 and the impact of surface phenomena on the reaction kinetics. The oxygenation of n-butyl and n-butoxy chains carrying trimethylsilyl, trimethoxysilyl, and tert-butyl groups with dioxirane 1 under homogeneous conditions confirms the electronic effects of the silyl substituents and the consequences of steric hindrance on the reaction rate and regioselectivity. Orthosilicic acid esters react preferentially at the methylene group adjacent to the oxygen atom in clear contrast with the reactivity of the carboxylic or sulfonic acid alkyl esters, which efficiently protect this position toward oxidation with 1.
authors: Departamento de Química Orgánica, Facultad de Farmacia, Universidad de Valencia, Avda. Vicente Andrés Estellés s.n., 46100-Burjassot, Valencia, Spain.
authors: Rossella
authors: R
authors: Mello
authors: Jaime
authors: J
authors: Martínez-Ferrer
authors: Ana
authors: A
authors: Alcalde-Aragonés
authors: Teresa
authors: T
authors: Varea
authors: Rafael
authors: R
authors: Acerete
authors: María Elena
authors: ME
authors: González-Núñez
authors: Gregorio
authors: G
authors: Asensio
mesh_terms: D002073:Butanes / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D004952:Esters / Q000737:chemistry; D005027:Ethylene Oxide / Q000031:analogs & derivatives* / Q000737:chemistry; D006860:Hydrogen Bonding; D007700:Kinetics; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D012996:Solutions; D013237:Stereoisomerism; D013499:Surface Properties
chemical_list: D002073:Butanes; D004952:Esters; D012996:Solutions; D012822:Silicon Dioxide; C445840:methyl(trifluoromethyl)dioxirane; D005027:Ethylene Oxide; D010100:Oxygen