The catalyzed thermal dissociation of aryl carbanilates in benzene

Abstract

Recent studies in the mechanism of thermal dissociation of N-substituted carbamates have shown a duality in the reaction mechanism, depending upon the number of N-substituents. The present research was undertaken to investigate the equilibrium by which aryl carbanilates dissociate at elevated temperatures and to show how such factors as structure and chemical environment relate to this equilibrium.

Members of a series of meta- and para-substituted phenyl carbanilates were shown to undergo a rapid reversible dissociation in benzene with the added catalyst, dibutyltin dilaurate. The equilibrium constants for this dissociation were measured at four different temperatures ranging from 90°C to 150°C. The thermodynamic parameters were calculated. The value of enthalpy (AH) ranges between 13.5 and 16.4 kcal/mole, and the entropy (AS) values were 25.1 to 32.1 e.u. Results obtained from the present research were compared with those from the dissociation of aryl carbanilates in glyme. Introduction of an electron- releasing group into the ester lowered the values of the equilibrium constants. On the other hand, the electron-attracting groups in the ester increased the values of equilibrium constants. A probable mechanism is proposed for this dissociation.