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      Flow through reactors for organic chemistry: directly electrically heated tubular mini reactors as an enabling technology for organic synthesis

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          Summary

          Until recently traditional heating in organic chemistry has been done with oil heating baths or using electric heat exchangers. With the advent of microwave equipment, heating by microwaves was rapidly introduced as standard method in organic chemistry laboratories, mainly because of the convenient possibility to operate at high temperature accompanied by accelerated reaction rates. In the present contribution we discuss the method of heating small, continuously operated reactors by passing electric current directly through the reactor wall as an enabling technology in organic chemistry. The benefit of this method is that the heat is generated directly inside the reactor wall. By this means high heating rates comparable to microwave ovens can be reached but at much lower cost for the equipment. A tool for the comparison of microwave heating and traditional heating is provided. As an example kinetic data for the acid catalyzed hydrolysis of methyl formate were measured using this heating concept. The reaction is not only a suitable model but also one of industrial importance since this is the main production process for formic acid.

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          Combining enabling techniques in organic synthesis: continuous flow processes with heterogenized catalysts.

          The concepts article describes enabling techniques (solid-phase assisted synthesis, new reactor design, microwave irradiation and new solvents) in organic chemistry and emphasizes the combination of several of them for creating new synthetic technology platforms. Particular focus is put on the combination of immobilized catalysts as well as biocatalysts with continuous flow processes. In this context, the PASSflow continuous flow technique fulfils both chemical as well as chemical engineering requirements. It combines reactor design with optimized, monolithic solid phases as well as reversible immobilization techniques for performing small as well as large scale synthesis with heterogenized catalysts under continuous flow conditions.
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            Asymmetric reactions in continuous flow

            Summary An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed.
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              A new concept for the noncovalent binding of a ruthenium-based olefin metathesis catalyst to polymeric phases: preparation of a catalyst on Raschig rings.

              A new concept for noncovalent immobilization of a ruthenium olefin metathesis catalyst is presented. The 2-isopropoxybenzylidene ligand of a Hoveyda-Grubbs carbene is further modified by an additional amino group (7) and immobilization is achieved by treatment with sulfonated polystyrene forming the corresponding ammonium salt. In this novel strategy for the immobilization of ruthenium-based metathesis catalysts, the amino group plays a two-fold role, being first an active anchor for immobilization and second, after protonation, activating the catalysts (electron donating to electron withdrawing activity switch). The polymeric support was prepared by precipitation polymerization which led to small bead sizes (0.2-2 microm) and large surface areas. Compared to commercial resins this tailor-made phase showed superior properties in immobilization of complex 7. This concept of immobilization was applied to glass-polymer composite megaporous Raschig rings. Ru catalyst 7 on Raschig rings was used under batch conditions in various metathesis reactions, including ring-closing (RCM), cross- (CM) and enyne metathesis, to give products of high chemical purity with very low ruthenium contamination levels (21-102 ppm). The same ring can be used for up to 6 cycles of metathesis.
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                Author and article information

                Contributors
                Role: Guest Editor
                Journal
                Beilstein J Org Chem
                Beilstein Journal of Organic Chemistry
                Beilstein-Institut (Trakehner Str. 7-9, 60487 Frankfurt am Main, Germany )
                1860-5397
                2009
                30 November 2009
                : 5
                : 70
                Affiliations
                [1 ]Institute of Chemical Process Engineering, Clausthal University of Technology, Leibnizstr. 17, D-38678 Clausthal-Zellerfeld (Germany)
                Article
                10.3762/bjoc.5.70
                2839532
                20300506
                b24e6398-fc6c-42f8-a351-32b437cacd63
                Copyright © 2009, Kunz and Turek; licensee Beilstein-Institut.

                This is an Open Access article under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: ( http://www.beilstein-journals.org/bjoc)

                History
                : 7 September 2009
                : 19 November 2009
                Categories
                Full Research Paper
                Chemistry
                Organic Chemistry

                Organic & Biomolecular chemistry
                direct electric heating,flow reactors,micro reactors,organic chemistry,reaction kinetics

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