INVESTIGADORES
BONIVARDI Adrian Lionel
congresos y reuniones científicas
Título:
MODULATED TRANSIENT EXPERIMENTS BY ATR-FTIR FOR THE IDENTIFICATION OF INTERMEDITES IN SOLID-LIQUID INTERPHASE
Autor/es:
S.E. COLLINS; L.E. BRIAND; A.L. BONIVARDI
Lugar:
Sao Pedro, Brasil
Reunión:
Simposio; Fifth San Luis Symposium on Sufaces, Interfaces and Catalysis; 2010
Resumen:
Attenuated total reflection (ATR) infrared (IR) spectroscopy is a powerful tool for the
investigation of reaction pathways in solid(catalyst)/liquid(reactive) systems, because it provides
the detection of species adsorbed on a catalyst under reaction conditions. However, the presence
of strongly absorbent solvents, spectator species and/or the catalyst itself can make very difficult
or preclude the identification and tracking of the true active species, that is, the intermediates.
Then, transient experiments are widely applied in the analysis of reaction intermediates by
perturbing a catalytic system working under steady state conditions (ss). For example,
modulation excitation spectroscopy (MES) with phase sensitive detection (PSD) have proved to
be an adequate methodology to separate a weak response from a strong background signal [Rev.
Sci. Instrum. 72(2001)3782]. MES-PSD is based on the disturbance of a ss system by the
periodical variation of an external parameter such as the temperature, the pressure, or the
concentration of a reactant. Therefore, all the species in the system that are affected by this
parameter will also change periodically with the same frequency of the perturbation, but with a
phase lag. Thus, MES-PSD applied to in situ ATR-IR experiments can allow the sensitive and
selective detection of species directly involved in a reaction at the liquid/solid interface, and the
monitoring of their dynamic behaviors.
In this work we studied the adsorption and decomposition of acetic anhydride in liquid phase on
phosphotunstic Wells-Dawson heteropoly acid (HPA) using MES-PSD coupled with ATR-IR.
The acyl [CH3C(O)+] intermediate species bonded to HPA was identified: vas(COO) = 1650
cm-1, vs(COO) = 1322 cm-1, d(CH) = 1455 cm-1. This very unstable species is produced by the
splitting of acetic anhydride molecule, and it is the key intermediate in the Friedel-Craft
acylation reaction of isobutylbencene towards p-isobutylacetophenone, which is a step of the
ibuprofen synthesis. The by-products of the reaction are acetic acid and acetate.