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Insights into the Organocatalyzed Synthesis of Urethanes in Supercritical Carbon Dioxide: An In Situ FTIR Spectroscopic Kinetic Study

Authors

  • Dr. Christopher A. Smith,

    1. Univ. Bordeaux, ISM, UMR 5255, F-33405 Talence Cedex (France), Fax: (+33) 540008402
    2. CNRS, ISM, UMR 5255, F-33405 Talence Cedex (France)
    3. Univ. Bordeaux, LCPO, UMR 5629, F-33607 Pessac Cedex (France)
    4. CNRS, LCPO, UMR 5629, F-33607 Pessac Cedex (France)
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  • Prof. Henri Cramail,

    1. Univ. Bordeaux, LCPO, UMR 5629, F-33607 Pessac Cedex (France)
    2. CNRS, LCPO, UMR 5629, F-33607 Pessac Cedex (France)
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  • Dr. Thierry Tassaing

    Corresponding author
    1. Univ. Bordeaux, ISM, UMR 5255, F-33405 Talence Cedex (France), Fax: (+33) 540008402
    2. CNRS, ISM, UMR 5255, F-33405 Talence Cedex (France)
    • Univ. Bordeaux, ISM, UMR 5255, F-33405 Talence Cedex (France), Fax: (+33) 540008402===

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Abstract

The kinetics of urethane (carbamate) formation in supercritical CO2 (scCO2) has been studied by in situ FTIR spectroscopy by using the reaction between n-butanol and toluene-2,4-diisocyanate as a model for the synthesis of polyurethanes. We have evaluated the efficiency of different organocatalysts for this transformation to eliminate the need for potentially toxic organotin compounds. Bicyclic guanidines and amidines (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene and 1,8-diazabicyclo[5.4.0]undec-7-ene) lead to a significant acceleration of the reaction rate, but we found that their activity in scCO2 is reduced compared to reactions in conventional media because of the formation of guanidinium or amidinium alkylcarbonate salts. In scCO2, these catalysts are also sensitive to the presence of water and can lead to the formation of allophanate or isocyanurate byproducts. On the other hand, we have shown that catalysis with amine N-oxides (N-methylmorpholine-N-oxide) is suited to the scCO2 medium.

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