Urethanes and polyurethanes bearing furan moieties-2. comparative kinetics and mechanism of the formation of furanic and other monourethanes

Abstract

The kinetics of the condensation of alcohols with isocyanates to give monourethanes were studied with the aim of establishing the reactivity of furanic reagents relative to those of aliphatic and aromatic homologues. Reactions were conducted under stoichiometric conditions using two different solvents at 70-110°. Among alcohols, furfuryl alcohol was found to be a little less reactive than its benzyl counterpart. Other furanic alcohols displayed reactivities in accordance with the nature of other substituents (steric vs field effects). Among isocyanates, the furyl parent showed an extremely high reactivity and even the furfuryl homologue turned out to be more reactive than phenyl isocyanate. The scope of this investigation was then extended to a more detailed examination of steric, conjugation and field effects on the reactivity of non-furanic alcohols and isocyanates. The results are discussed in the light of previous less systematic studies and a suitable mechanism is envisaged. All the reactions followed second-order behaviour up to high conversions. © 1989.