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Issue 4, 2018
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Synthesis of Boscalid via a three-step telescoped continuous flow process implemented on a MJOD reactor platform

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Abstract

A three step continuous/semi-flow process leading to the fungicide Boscalid® is disclosed. The first step of the process is a Suzuki cross-coupling where 1-chloro-2-nitrobenzene is coupled with 4-chlorophenylboronic acid at a temperature of 80 °C using a solvent mixture of ethanol/water as the reaction medium with sodium carbonate as the base and tetrakis(triphenylphosphine)-palladium as the catalyst. This reaction step was developed as a batch procedure and then adapted and implemented on a multi-jet oscillating disk (MJOD) continuous flow reactor platform. The intermediate 4′-chloro-2-nitro-1,1′-biphenyl was achieved in high yield (82%). The second step which was telescoped with the first one involved a nitro group reduction of high efficacy. The reduction method was based on NaBH4/CoSO4·7H2O as the reduction system. The reduction product 2-amino-4′-chloro-1,1′-biphenyl was achieved in high yield (79%) at a short reactor residence time (3 min). The final step of the process is composed of a two-step sequence where 2-amino-4′-chloro-1,1′-biphenyl is transformed into the corresponding iminosulfanone intermediate (not isolated), which immediately reacts with the 2-chloronicotinic acid present in the reaction mixture to form Boscalid® in a yield of >66%. The three-step process provided an overall yield of >42%, which corresponds to a mean step yield of ≈75%.

Graphical abstract: Synthesis of Boscalid via a three-step telescoped continuous flow process implemented on a MJOD reactor platform

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Publication details

The article was received on 28 Mar 2018, accepted on 22 Jun 2018 and first published on 23 Jun 2018


Article type: Paper
DOI: 10.1039/C8RE00049B
Citation: React. Chem. Eng., 2018,3, 550-558

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    Synthesis of Boscalid via a three-step telescoped continuous flow process implemented on a MJOD reactor platform

    A. Drageset, V. Elumalai and H. Bjørsvik, React. Chem. Eng., 2018, 3, 550
    DOI: 10.1039/C8RE00049B

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