Reactions of monoisocyanates with alcohols, as model compounds

1 Reactions of monoisocyanates with alcohols, as model compounds 

The kinetics of urethane formation from monoisocyanates and alcohols have been studied in extensive detail, and serve as a useful guide for 

Brock [22] showed that the reaction of aryl isocyanates with alcohols could be correlated by the Hammett [14] linear free energy relationship, log fe/feo = p2o. Using data from published sources, with reaction temperatures in the range of 20—39.69°C and using several solvents, the value for p was calculated to be 1.69. Substituent constants (a) were given by Brock and also by Kaplan [123]. 

Aliphatic isocyanates are generally much less reactive than phenyl isocyanate. The work of O Brien and Pagano [125] showed an activation energy of 16 kcal mole for the reaction between tert-octyl isocyanate and ethanol at 25—40°C, and 22 kcal mole for reaction with 2-butanol. These relatively high activation energies are apparently typical for aliphatic isocyanates. 

Although reactions of aromatic isocyanates with alcohols generally follow second-order kinetics or modified second-order kinetics as outlined by Baker and Holdsworth [19], Sato [126] reported that aliphatic and edkenyl isocyanates were much more subject to alcohol and urethane catalysis. The reactions of these compounds were found to ee with the expression 

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