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- Author or Editor: Ferenc Darvas x
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Abstract
On behalf of the Flow Chemistry Society, it is my great pleasure to welcome you all in the first issue of the Journal of Flow Chemistry.
For successful deep space exploration, a vast amount of chemistry-related challenges has to be overcome. In the last two decades, flow chemistry has matured enough to take the lead in performing chemical research in space. This perspective article summarizes the state of the art of space chemistry, analyzes the suitability of flow chemistry in extraterrestrial environment, and discusses some of the challenges and opportunities in space chemistry ranging from establishing an end-to-end microfactory to asteroid mining.
Quaternary pyridinium aldoximes have been analyzed by thin-layer chromatography. Their separation was adequate when silica plates were used with a mobile phase with a high water content. As a consequence of their limited migration, reversed-phase TLC was not appropriate for determination of the lipophilicity of quaternary pyridinium aldoximes. Displacement TLC of some quaternary pyridinium aldoximes is, nevertheless, possible using silica as stationary phase with water-acetone-hydrochloric acid mobile phases. Normal-phase TLC with different concentrations of organic modifier gave a series of R M values for the pyridinium aldoximes. Approximation of the different plots of R M against organic modifier concentration to straight lines afforded R M,0 values and the slopes of the lines. The R M,0 values and the slopes both serve as indicators of the hydrophilic character of the compounds.
Abstract
The atom economy concept is one of the earliest recognition for green and sustainable aspects of organic synthesis. Over the years, novel technologies emerged that made this important feature of reactions into practice. Continuous-flow devices increased the efficiency of the chemical transformations with novel process windows (high T, high p and heterogeneous packed catalysts etc.) and increased safety which turned the attention to reexamine old, industrial processes. Oxidation can be performed under flow catalytic conditions with molecular oxygen; alcohols can be oxidized to carbonyl compounds with high atom economy (AE = 87 %). Using O2 and 1 % Au/TiO2, alcohol oxidation in flow was achieved with complete conversion and >90 % yield. N-alkylation is another good example for achieving high atom economy. Under flow catalytic conditions (Raney Ni), amines were successfully reacted with alcohols directly (AE = 91 %) with >90 % conversion and selectivity. In both examples, the effective residence time was less than 1 min. These two examples demonstrate the significant contribution of flow technology to the realization of key principles in green and sustainable chemistry.
Abstract
Highly active immobilized hydrogenation catalytic systems were used in the H-Cube™ hydrogenation reactor. “In situ” produced [Rh(COD)((S)-MonoPhos)2]BF4 complex was immobilized on commercially available Al2O3 and mesoporous Al2O3 by means of phosphotungstic acid (PTA), respectively. The optimum reaction conditions were determined and studied at different temperature, pressure, and flow rate values. Furthermore, the effect of the substrate concentration, microstructure of the support, and the stability of the complex were investigated. A continuous-flow reaction system using a stationary-phase catalyst for the asymmetric hydrogenation of methyl acetamidoacrylate was developed and run continuously for 12 h with >99% conversion and 96–97% enantioselectivity.
A novel method for C–H functionalization of heteroaromatic rings by using continuous-flow reactors is reported. Direct alkylation reactions were investigated under heterogeneous catalytic conditions using simple transition metal catalysts at elevated temperature and pressure. As a model reaction, the alkylation of indole was attempted using cheap Raney® Nickel catalyst. Alcohols served both as alkylating agent and as reaction media. The targeted 3-alkyl-indoles were obtained in moderate to good yield with reasonable selectivity. Transient protection on the N-atom increased the selectivity up to 80%. The scope and limitations were also investigated. In summary, direct alkylation with alcohols represents a rapid (residence time of <1 min) and traceless process with high atom economy (88–92%, in those cases where transient protection was not applied).
