Commercial silica materials functionalized with a versatile organocatalyst for the catalysis of acylation reactions in liquid media.

Abstract

Silica materials represent a promising material for the application in heterogeneous organocatalysis due to their readily modifiable surface and chemical inertness. To achieve high catalyst loadings, usually, porous carriers with high surface areas are used, such as special silica monoliths or spherical particles for backed bed reactors.  Yet, their synthesis is elaborate, and thus less complex and cheaper alternatives are of interest, especially considering scaling up. In this work, two commercial silica materials functionalized with the organocatalyst 4-(dimethylamino)pyridine (DMAP) were used in catalytic acylation reactions: a mesoporous silica gel (Siliabond®-DMAP) and non-porous silica nanoparticles (Ludox®). Both were successfully used in the acylation of phenylethanol, but the latter required significantly longer reaction times, presumably due to mass-transfer limitations as a consequence of substantial agglomeration that limits the accessible amount of catalyst. Furthermore, it was shown that the influence of the linker molecule is negligible, since both reaction yields and the activation energy remain largely similar. As main result the commercial material Siliabond-DMAP, despite the non-uniform particles, exhibited significant yield in a flow setup, thus demonstrating the potential as support material for application in heterogeneous organocatalysis.