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Dendrimer-encapsulated Au/Ag alloy nanoparticles (Au/Ag DENs) were covalently attached to a monolayer-functionalized inner surface of glass microreactors. The influence of the bimetallic alloy structure and of the different metal ratios was investigated for the reduction of 4-nitrophenol using NaBH4. TheAu/Ag—dendrimer nanocomposite with a 1:1 Au/Ag metal ratio showed the highest activity as compared to othermetal ratios and to pure Ag and Au. The dendrimer template exerted a stabilizing effect for six consecutive days of use with almost no decrease in conversion. This strategy enables the screening and investigation of a variety of bimetallic nanocatalysts in continuous-flow microreactors.

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Abstract

The inner walls of a glass microreactor were functionalized in a one-step procedure with a single layer of a strong perfluoroalkylsulfonic acid. The applicability of the catalytic device was demonstrated in the successful hydrolysis of benzaldehyde dimethyl acetal in acetonitrile, achieving quantitative conversion within a residence time of only 60 s. Furthermore, the catalytic system showed high conversion for the Friedlander quinoline synthesis between 2-aminobenzophenone and ethyl acetoacetate. The cyclization of pseudoionone in methylcyclohexane proved the wide applicability of the acid-functionalized microreactor also for reactions carried out in apolar media. The platform showed activity for 6 h to 2 days, depending on the solvent, and was reactivated by simple treatment with the catalyst precursor.

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Abstract

The covalent attachment of piperazine onto the inner walls of a microreactor using glycidyl methacrylate polymer brushes has been demonstrated. The piperazine-containing polymer brushes were first grown on a flat silicon oxide surface and were characterized by contact angle, Fourier transform infrared (FT-IR), ellipsometry, and X-ray photoelectron spectroscopy (XPS). The applicability of the catalytic polymer brushes in a microreactor was demonstrated for the Knoevenagel and nitroaldol condensation reactions, and the synthesis of coumarin derivatives. The catalytic activity of the microreactor was still intact even after 2 months.

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Journal of Flow Chemistry
Authors:
Rajesh Munirathinam
,
Andrea Leoncini
,
Jurriaan Huskens
,
Herbert Wormeester
, and
Willem Verboom

Cinchona alkaloid and proline derivatives as enantioselective catalysts were covalently attached onto the inner walls of a microreactor using glycidyl methacrylate polymer brushes. The successful formation of the organocatalyst-functionalized brush layers on flat silicon oxide surfaces was confirmed by several techniques such as Fourier transform infrared (FT-IR), ellipsometry, and X-ray photoelectron spectroscopy (XPS). The applicability of the cinchona alkaloid (cinchonidine or quinidine)- and proline-containing polymer brushes in a microreactor was demonstrated for the Diels–Alder reaction between anthrone and N-substituted maleimides, and the aldol reaction between 4-nitrobenzaldehyde and cyclohexanone, respectively, which showed moderate conversions (up to 55% and 23%, respectively) and moderate to good enantioselectivities (up to 55% and 93%, respectively). The pristine catalytic activity of the microreactor was intact even after 1 month.

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Abstract

The reaction of different types of aromatic and aliphatic epoxides with sodium azide to give vicinal azido alcohols was studied in a microreactor with and without pillars in the channels. Dependent on the substrate, the regioselectivity of the ring opening is affected by the used solvent system, viz. acetonitrile–water (sometimes with 10% acetic acid to promote the reactivity of substrates) or t-butyl acetate–water containing Tween80 as a surfactant. For styrene oxide and α-methylstyrene oxide, the α/ß regioselectivity changes from 4 to 10 and 1.7 to 6.2, respectively, going from acetonitrile–water to Tween80-containing t-butyl acetate–water. The addition of a surfactant (Tween80) stabilizes the interface in the biphasic t-butyl acetate–water. Pillar-containing microreactors gave better conversions than microreactors without pillars and lab scale reactions, probably due to better mixing.

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