Janus Interphase Organic-Inorganic Hybrid Materials: Novel Water-Friendly Heterogeneous Catalysts

In this work, amphiphilic silica-based Janus-type acid and base catalysts are introduced as heterogeneous analogues of surfactants. The new interphase organic-inorganic hybrid catalysts comprise of two different groups (-C8H17, -C2H4Ph) on the hydrophobic and two different groups (-C3H6SO3H, -C3H6NH2) on the hydrophilic side. The hydrophobic sides of the catalysts are responsible for the diffusion of the organic substrates to the catalytically active sites while the hydrophilic sides carry catalytic centers being oriented towards the aqueous phase and thus providing sufficient connection between water (solvent) and the organic substrates. Catalyst preparation is based on simple synthetic procedures and leads in a first step to hollow silica spheres with hydrophobic groups on the inner and hydrophilic groups on the outer surface. After crushing the hollow spheres, acid resp. base functionalized Janus nano-sheets are obtained. The basic catalyst was tested for the Knoevenagel condensation of a series of benzaldehydes with malononitrile in water, while the acid catalyst was used for Fischer esterification of acetic acid with ethanol.