Klaus Jähnisch

Green and Efficient Synthesis of Sulfonamides Catalyzed by Nano-Ru/Fe3O4

The environmentally benign synthesis of carbon-nitrogen bonds continues to be an active and challenging field of chemical research. Here, a novel, environmentally benign method for the direct coupling of sulfonamides and alcohols is described. Despite the importance of sulfonamide derivatives as intermediates in drug synthesis, till now such transformations are rarely known. For the first time a domino dehydrogenation-condensation-hydrogenation sequence of alcohols and sulfonamides has been realized in the presence of a nanostructured catalyst. The magnetic property of the catalyst system allows for convenient isolation of the product and efficient recycling of the catalyst. A variety of coupling reactions of benzylic alcohols and sulfonamides including various heterocycles were successfully realized, often with >80% isolated yield. Advantageously, only one equivalent of the primary alcohol is consumed in the process. Mechanistic investigations of the competitive reactions of benzyl alcohol and d(7)-benzyl alcohol with p-toluenesulfonamide revealed a kinetic isotope effect (k(H)/k(D)) of 2.86 (+/-0.109) for the dehydrogenation of benzyl alcohol and 0.74 (+/-0.021) for the hydrogenation of N-benzylidene-p-toluenesulfonamide intermediate, which suggests dehydrogenation of the alcohol to be the rate determining step.

Application of microstructured reactor technology for the photochemical chlorination of alkylaromatics

The advantageous application of a falling-film microreactor for a photochemical gas/liquid reaction was demonstrated by the selective photochlorination of toluene-2,4-diisocyanate (TDI) In the microstructured reactor the selectivity to the side-chain chlorinated product 1 -chloromethyl-2,4-diisocyanatobenzene (1CI-TDI) achieved a value of 80% at 55% TDI conversion, whereas the side product toluene-5-chloro-2,4-diisocyanate (5CI-TDI) was formed with only 5% selectivity. The yield of 1CI-TDI was enhanced by increasing the residence time from 24% after 5 s to 54% after 14 s. At the same time the formation of consecutive products increased and the selectivity to 1CI-TDI decreased to 67% after 14 s residence time. The influence of the reactor material was shown. In presence of a Lewis acid such as FeCl 3 , formed by chlorination using a reaction plate made of iron, consecutive products were formed and the selectivity to 1CI-TDI was lowered. The microstructured reactor led to remarkably higher selectivities than the conventional batch reactor, where the selectivity to 1CI-TDI was only 45% at 65% TDI conversion and the side product 5CI-TDI was formed with 50% selectivity. The space-time yield of 1CI-TDI achieved in the microstructured reactor (400 mol I - 1 h - 1 ) clearly exceeded the performance of the batch reactor (space-time yield 1.3 mol I - 1 h - 1 ). Based on the microreactor data, a kinetic model for the TDI chlorination including by-product formation was suggested and used to predict product selectivity at full TDI conversion.

On the selective aerobic oxidation of benzyl alcohol with Pd/Au-nanoparticles in batch and flow

Abstract Nanoparticles (NP) have specific catalytic properties, which are influenced by parameters like their size, shape, or composition. Bimetallic NPs, composed of two metal elements can show an improved catalytic activity compared to the monometallic NPs. We, herein, report on the selective aerobic oxidation of benzyl alcohol catalyzed by unsupported Pd/Au and Pd NPs at atmospheric pressure. NPs of varying compositions were synthesized and characterized by UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The NPs were tested in the model reaction regarding their catalytic activity, stability, and recyclability in batch and continuous procedure. Additionally, in situ extended X-ray absorption fine structure (EXAFS) measurements were performed in order to get insight in the process during NP catalysis.