Pickering emulsion droplets hosting ionic liquid catalysts for continuous-flow cyanosilylation reaction

Abstract

Based on the confinement of Pickering emulsion droplets, a novel method to “immobilize” IL catalysts has been developed successfully for continuous-flow cyanosilylation reaction.

Catalysis in Pickering emulsions

“…ILs have been identified as efficient catalysts for the cyanosilylation of carbonic compounds. 45 Moreover, they can replace the harmful dichloroethane often used as the reaction medium in this transformation. One drawback of ILs however is their relatively high viscosity.…”

“…44 Therefore, if this reaction is conducted in batch, mechanical agitation is not particularly efficient and can hamper the production at large scale. 45 However, in Pickering emulsions, bulk IL is broken into numerous droplets on the micrometer scale which increases the interfacial area and benefits fast diffusion of reactants and products without the need for agitation. As mentioned above, enzymes can be dissolved in ILs, and this phase can be used to prepare IL/o Pickering emulsions.…”

“…47 ILs can even in some cases enhance the selectivity of a reaction. 43,45,46,48 Tao et al carried out the hydroformylation of long chain alkenes in an IL/o Pickering emulsion system. 48 The overall catalytic performance was superior to that of a w/o system.…”

“…3(c)) for biofuel upgrading reactions is given by Zapata et al 63 Apart from enzymes, other types of catalysts have been used for PAC, such as acids or bases, 55,65-67 metallic catalysts 48,68 and even ionic liquids. 45 Yang et al use HCl and NaBH 4 in w/o Pickering emulsions stabilized with partially hydrophobic silica nanospheres for a deacetalization-reduction cascade reaction. 66 Silica particles are also used as the particulate emulsifier by Xue and co-workers, where H 2 SO 4 and ethylenediamine are the catalysts for the deacetalization-Knovenagel condensation cascade reaction in w/o Pickering emulsions.…”

“…The conversion increased with decreasing the emulsion droplet size which led to larger interfacial areas. 43 A further example of the use of IL is that given by Meng et al 45 A continuous-flow cyanosilylation reaction system is developed based on the confinement of one catalytically active IL catalyst dissolved within the other IL droplets in an IL/o Pickering emulsion. The conventional batch reactor gave a catalytic efficiency of 9.1 mol mol À1 h À1 .…”