A new concept for preparing pyrazolidine by the oxidation of 1,3-diaminopropane. Synthesis and formulation of a kinetic model

The present study describes a new way of preparing pyrazolidine by intramolecular Raschig amination using 1,3-diaminopropane and sodium hypochlorite. A global process has been developed, involving the characterization of the reaction mechanisms, kinetic studies and the optimization of the synthesis parameters. The rates were determined as a function of the reagent concentrations, pH and temperature. The overall reaction, of the first order with respect to both reagents, is the result of two successive mechanisms: the first being pH independent, the second accelerated by increasing pH. The bimolecular rate was simulated as a function of hydroxide ion activity. The activation enthalpy and entropy of the molecular process were established at 25 °C. A kinetic model is proposed and then validated by the experimental results. Finally, it was found that the yield of pyrazolidine essentially depends on the ratio p ([1,3-diaminopropane]0/[sodium hypochlorite]0) of the initial molar concentrations and the ratio of the rates k2/k1 (k1: rate of the N,N-dichloro-1,3-diaminopropane formation and k2: rate of N-chloro-1,3 diaminopropane formation).