Kinetic and Mechanistic Studies of Carboxylic Acid–Bisoxazoline Chain‐Coupling Reactions

Kinetic studies of the reactions between a model carboxylic acid and bisoxazoline coupling agents, namely 2,2′‐(1,3‐phenylene)bis(2‐oxazoline) (mbox), 2,2′‐(1,4‐phenylene)bis(2‐oxazoline) (pbox), and 2,2′‐(2,6‐pyridylene)bis(2‐oxazoline) (pybox), were carried out in bulk at 140–220 °C. A second‐order two‐step reaction mechanism was proposed and was verified by the experimental results. The results also indicate that the reactivity of the oxazoline groups is unchanged after the reaction of the other oxazoline group of the same coupling agent moiety, that is, oxazoline groups are equireactive. Rate constants and activation enthalpies and entropies were determined, allowing the comparison of bisoxazoline reactivity. The following reactivity order was found: pybox > mbox > pbox. The formation of a stabilized protonated complex is postulated to explain the much higher reaction rate observed with the new coupling agent pybox. Variation of the experimental concentrations of reactants and reaction products versus time. magnified image Variation of the experimental concentrations of reactants and reaction products versus time.