Nanoscale Organization of Thiol and Arylsulfonic Acid on Silica Leads to a Highly Active and Selective Bifunctional, Heterogeneous Catalyst

Abstract

Ordered mesoporous silicas functionalized with alkylsulfonic acid and thiol group pairs have been shown to catalyze the synthesis of bisphenols from the condensation of phenol and various ketones, with activity and selectivity highly dependent on the distance between the acid and thiol. Here, a new route to thiol/sulfonic acid paired catalysts is reported. A bis-silane precursor molecule containing both a disulfide and a sulfonate ester bond is grafted onto the surface of ordered mesoporous silica, SBA-15, followed by simultaneous disulfide reduction and sulfonate ester hydrolysis. The resulting catalyst, containing organized pairs of arylsulfonic acid and thiol groups, is significantly more active than the alkylsulfonic acid/thiol paired catalyst in the synthesis of bisphenol A and Z, and this increase in activity does not lead to a loss of regioselectivity. The paired catalyst has activity similar to that of a randomly bifunctionalized arylsulfonic acid/thiol catalyst in the bisphenol A reaction but exhibits greater activity and selectivity than the randomly bifunctionalized catalyst in the bisphenol Z reaction.

A simpler and highly efficient protocol for the preparation of biodiesel from soap stock oil using a BBSA catalyst

“…27 In order to measure the sulfonic acid density, the sulfur content of BBSA catalyst has been measured by elemental analysis. The total acidity of the bagasse based solid acid catalyst was 1.9 mmol g -1 , which was determined through the neutralization titration.…”

Supported Molecular Catalysts: Synthesis, In-Situ Characterization and Performance

“…This catalyst gave the best overall performance [6]. The acid/thiol combination provided an example where the two organic groups should be positioned as close to one another as possible.…”

The effect of the distance between acidic site and basic site immobilized on mesoporous solid on the activity in catalyzing aldol condensation

“…In addition, bifunctional groups in pairs may be beneficial to achieve cooperative effect. Davis et al have synthesized acid/thiol paired catalysts involving the design of an organosilane precursor [29,30]. Also, Katz and Bass developed a method to synthesize the thiol/amine paired catalysts based on a xanthate protection strategy to control thiol/amine distance [31].…”