Acidity and reactivity of trifluoromethanesulfonic acid in liquid and solid acid catalysts

Abstract

The acidic properties of CF 3 SO 3 H/SiO 2 acid catalysts have been investigated by the protonation of weak bases (B) (B+H + BH + ) and the proton-transfer process from (H + A − ) to (BH + A − ) has been analysed by a thermodynamic procedure used to account the variation of the activity coefficient terms of the species involved. Acid-base systems with different substituted pyridines as back-titrating agents of BH + (i.e. BH + → B) have also been studied and the changes observed in the acid-base interactions according to basicity of pyridines are discussed. The results in solid phase have been compared with those observed in concentrated aqueous solutions (i.e. CF 3 SO 3 H + H 2 O) where "acidity" and "protonating ability" have been distinguished as parameters of interest in the description of nonideal acid systems.Silica loaded with CF 3 SO 3 H, with H 2 SO 4 and with a mixture of both acids have been tested in acid catalysed reactions and their catalytic effectiveness has been explored towards substrates with high acid requirements for the conversion reagents-products. From the available observations in liquid and in solid phase, CF 3 SO 3 H has been proved to be a less effective acid catalyst than expected from the observed protonating ability of acidic medium. Strong interactions between ionic species and the involvement of ion-pairs in concentrated acid systems have been suggested.

Preparation of Highly Active Triflic Acid Functionalized SBA‐15 Catalysts for the Synthesis of Coumarin under Solvent‐Free Conditions

“…It can be seen that the total acidity of the TFA‐functionalized SBA‐15‐100 catalysts increased gradually with increasing TFA loading. By considering the thermal stability of TFA, a maximum temperature of 300 °C was set for the TPD measurements . The profiles for the TPD of ammonia of TFA‐functionalized SBA‐15 with different pore diameters are shown in Figure .…”

On the Beckmann rearrangement of ketoximes: A kinetic study in trifluoromethanesulfonic acid

“…The final aim of the work is an extension of analogous studies over selected solid catalysts already tested in some acid catalyzed reactions [15][16][17]. Indeed, owing to the critical issues associated with the Beckmann rearrangement of ketoximes in aqueous strong acids or superacids, alternative reaction conditions supporting the need for more environmentally benign systems are continuously attempted.…”

Conversion of Fructose and Xylose into Platform Chemicals Using Organo‐Functionalized Mesoporous Material

“…The total acidity of the catalyst (determined by TPD of ammonia technique) is responsible for the difference in product yield and reported in prior publication . The TPD experiment was carried out in the maximum temperature of 300 ° C because of possibility of bond breaking between triflic acid molecules and silanol groups of solid silica surface of KIT‐5 mesoporous materials . This trend finds the correlation with the increase in the density of acid site on the surface of the TFA functionalized KIT‐5 catalysts.…”