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

Abstract

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.

Fast and Selective Aqueous-Phase Oxidation of Styrene to Acetophenone Using a Mesoporous Janus-Type Palladium Catalyst

“…All chemicals and solvents were purchased from the suppliers and used without further purifications except pentane and toluene, which were dried before use. Solid state 13 C and 29 Si CP-MAS NMR spectra were measured using a 500 MHz BRUKER Avance III spectrometer under cross polarization conditions with a spinning frequency of 11,000 Hz for both 13 C and 29 Si and with scan numbers of 15,000 and 2500, respectively. TGA measurements were performed in synthetic air (20.5% O 2 in N 2 ) on a SETARAM-Setsys-16 from 30 • C to 900 • C with a heating ramp of 10 K min −1 .…”

“…Material 1 was prepared according to our previously described procedure [29] followed by the crushing of the resulted hollow particles using mortar and pestle for 30 min. Yield: 1.15 g. Elemental analysis: C: 6.72% and H: 2.15%.…”

“…To this aim, we introduced simple and practical techniques for the synthesis of heterogeneous Janus-type interphase catalysts by a modification of the Stöber process [29][30][31]. The catalysts showed high activity for the synthesis of a series of fine chemicals.…”

A Janus‐type Heterogeneous Surfactant for Adipic Acid Synthesis

“…A novel sub‐group of these materials are anisotropically functionalized catalysts so‐called Janus interphase catalysts. Very recently, we published a simple and practical procedure for the preparation of such Janus interphase catalysts . In the present manuscript we report the synthesis of the first amphiphilic and water dispersible Janus interphase Brønsted acid catalyst and its application as a heterogeneous analogue of a PTC for the aqueous‐phase oxidation of cyclohexene to adipic acid.…”

“…The analyses were repeated six times and the results indicate an excellent reproducibility of the measured data. In our previous report, we investigated two different hydrophobic/hydrophilic catalysts by means of this analytic method. In these cases, the formation of some temporary agglomerations of Janus‐type nanosheets in the solution was found, leading to particles with diameters of up to 30 μm.…”