Artículos de revistas
The gas-phase alcoholysis of protonated homoleptic alkoxysilanes
Fecha
2010Registro en:
EUROPEAN JOURNAL OF MASS SPECTROMETRY, v.16, n.3, Special Issue, p.379-388, 2010
1469-0667
10.1255/ejms.1077
Autor
RAINONE, Raquel
MALASPINA, Thaciana
XAVIER, Luciano A.
RIVEROS, Jose M.
Institución
Resumen
Tetra-alkoxysilanes are common and useful reagents in sol-gel processes and understanding their reactivity is important in the design of new materials. The mechanism of gas-phase reactions that mimic alcoholyis of Si(OMe)(4) (usually known as TMOS) under acidic conditions have been studied by Fourier transform ion cyclotron resonance techniques and density functional calculations at the B3LYP/6-311+G(d,p) level. The proton affinity of TMOS has been estimated at 836.4 kJ mol(-1) and protonation of TMOS gives rise to an ionic species that is best represented as trimethoxysilyl cations associated with a methanol molecule. Protonated TMOS undergoes rapid and sequential substitution of the methoxy groups in the gas-phase upon reaction with alcohols. The calculated energy profile of the reaction indicates that the substitution reaction through an S(N)2 type mechanism may be more favorable than frontal attack at silicon. Furthermore, the sequential substitution reactions are promoted by a mechanism that involves proton shuttle from the most favorable protonation site to the oxygen of the departing group mediated by the neutral reagent molecule.