Synthesis of N‐Aminopyrrolidine by the Raschig Process: Kinetic and Mechanistic Study of the Monochloramine‐Pyrrolidine Interaction

1-Pyrrolidinamine (NAPY) belongs to a family of large compounds, namely the alkylhydrazines, used as precursors for different targets in fine chemicals, such as pharmaceuticals and cosmetics. Different synthetic methods are described in the literature; however, many of them are not adaptable on a large scale. The Raschig process appears to be the most relevant method for preparing hydrazines at the industrial scale: hydrazines are obtained by two successive reactions. The first involves the formation of monochloramine from sodium hypochlorite and excess ammonia. The second consists of reacting, in a basic medium, the monochloramine previously synthesized with excess amine to provide the corresponding hydrazine. It is a clean and selective method, distinguished by its nonpolluting aspect, its low cost, and the feasibility of continuous transposition to industrial scale. However, it presents some disadvantages linked to the low hydrazine concentrations in the synthesis solutions. The optimization of the synthesis parameters is therefore essential and requires a detailed kinetic and mechanistic study of the reaction of NAPY formation by the chloramine/pyrrolidine interaction. The kinetics of the NAPY formation reaction were studied in alkaline medium, at first at a temperature of 25°C. Excess pyrrolidine was used with respect to NH2Cl, in order to minimize the influence of side reactions. Owing to the high reaction rates, the essays were carried out in a dilute medium, using reagent concentrations ranging between 1 × 10−3 and 4 × 10−2 M. The ionic strength of the medium was established by NaOH concentration (0.1 M). Then, the influence of the temperature was studied between 15 and 45°C for NH2Cl and PY concentrations, respectively, equal to 2 × 10−3 and 0.01 M, in order to check the conformance to the Arrhenius law. Finally, the characterization of the reaction mixture permitted establishment of a global reaction scheme, including two main secondary reactions.