Kinetic study of thermal degradation of 2-amino-2-methyl-1-propanol to cyclic 4,4-dimethyl-1,3-oxazolidin-2-one

Through initial rate data, the apparent (power law-PL) and mechanistic rate equations for the thermal degradation of 2-amino-2-methyl-1-propanol (AMP) to 4,4-Dimethyl-1,3-oxazolidin-2-one (DMOZD) as function of amine and CO₂ concentration in the solution were extracted. The reaction kinetics parameters including activation energies and pre-exponential factors for both approaches were defined.1, 2 Experimental Conditions: The rate experiments were carried out at 120, 135 and 150 °C, in the aqueous solutions of 1.12 - 3.36 M, AMP and CO₂ loadings of 0.17- 0.7, mol_CO2/mol_AMP. Method of Analysis: IC and HPLC/MS have been used for AMP and DMOZD, analysis, respectively. Results: Power law and mechanistic approach both present good prediction from experimental data. While mechanisms (II) and (III) have reasonable estimations, mechanism (I) with adjustable reaction order, has best prediction from experimental data. However, results from mechanism (III) provide the activation energy of 23.91 (kJ/mol) for the forward reaction of AMP with CO₂ to form a zwitterion, and 24.47 (kJ/mol) for the reverse reaction, i.e. zwitterion conversion to AMP and CO₂, both values are fairly consistent with literature reported values. According to the mechanism (III) zwitterion shows higher tendency to decay to its predecessor reactants, k₁/k_-1 0.03. Conclusion: The temperature dependent reaction rate constant for the power law rate equation varies from 16 10^-9 (mol/L)^(1-a-b).s^{- 1} at 120 °C to 26 10^-8 (mol/L)^(1-a-b).s^-1 at 150 °C. In the case of k₂<<k_-1, the reaction rate model extracted from mechanism (I), can simply reduce to power law equation. Considering different mechanisms and non-integer reaction orders for reactants demonstrates that the actual reaction mechanism may be more complex.