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Molecules 2016, 21(1), 24;

Reduced Reactivity of Amines against Nucleophilic Substitution via Reversible Reaction with Carbon Dioxide

Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC 29634, USA
Author to whom correspondence should be addressed.
Academic Editor: Jason P. Hallett
Received: 6 November 2015 / Revised: 7 December 2015 / Accepted: 13 December 2015 / Published: 23 December 2015
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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The reversible reaction of carbon dioxide (CO2) with primary amines to form alkyl-ammonium carbamates is demonstrated in this work to reduce amine reactivity against nucleophilic substitution reactions with benzophenone and phenyl isocyanate. The reversible formation of carbamates has been recently exploited for a number of unique applications including the formation of reversible ionic liquids and surfactants. For these applications, reduced reactivity of the carbamate is imperative, particularly for applications in reactions and separations. In this work, carbamate formation resulted in a 67% reduction in yield for urea synthesis and 55% reduction for imine synthesis. Furthermore, the amine reactivity can be recovered upon reversal of the carbamate reaction, demonstrating reversibility. The strong nucleophilic properties of amines often require protection/de-protection schemes during bi-functional coupling reactions. This typically requires three separate reaction steps to achieve a single transformation, which is the motivation behind Green Chemistry Principle #8: Reduce Derivatives. Based upon the reduced reactivity, there is potential to employ the reversible carbamate reaction as an alternative method for amine protection in the presence of competing reactions. For the context of this work, CO2 is envisioned as a green protecting agent to suppress formation of n-phenyl benzophenoneimine and various n-phenyl–n-alky ureas. View Full-Text
Keywords: carbamate; urea; benzophenoneimine; green chemistry carbamate; urea; benzophenoneimine; green chemistry

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Mohammed, F.S.; Kitchens, C.L. Reduced Reactivity of Amines against Nucleophilic Substitution via Reversible Reaction with Carbon Dioxide. Molecules 2016, 21, 24.

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