Preparation of Mono- and Diisocyanates in Flow from Renewable Carboxylic Acids

    • Michael D. Burkar1
    • Thien An Phung Hai1
    • Laurent J. S. De Backer2
    • Nicholas D. P. Cosford2
    • 1Department of Chemistry and Biochemistry and The California Center for Algae Biotechnology, University of California, San Diego, La Jolla, California 92093-0358, United States
    • 2Cancer Metabolism & Signaling Networks Program, NCI-Designated Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037, United States

    Diisocyanates used in polyurethanes are commonly prepared by phosgenation of petroleum-sourced diamines. This involves highly toxic phosgene and produces corrosive HCl, limiting synthetic applications. In our search for a renewable source for diisocyanates, we have developed a practical methodology for the production of isocyanates from algae-biomass-derived fatty acids or other renewable sources. This technique utilizes flow chemistry to prepare and convert high-energy intermediates, thus mitigating safety concerns. By the use of continuous flow, acyl azides are prepared from hydrazides and subsequently heated to undergo Curtius rearrangement, affording isocyanates in one scalable process. The method is efficient, safe, and sustainable, offers an opportunity to prepare isocyanates and diisocyanates from renewable feedstocks, and is amenable to distributed manufacturing processes.

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