35337-56-5Relevant academic research and scientific papers
Ammonia-dimethylchloramine system: Kinetic approach in an aqueous medium and comparison with the mechanism involving liquid ammonia
Stephan,Pasquet,Elkhatib,Goutelle,Delalu
, p. 340 - 351 (2008)
After an exhaustive study of the system ammonia-dimethylchloramine in liquid ammonia, it was interesting to compare the reactivity of this system in liquid ammonia with the same system in an aqueous medium. Dimethylchloramine prepared in a pure state undergoes dehydrohalogenation in an alkaline medium: the principal products formed are N-methylmethanimine, 1,3,5- trimethylhexahydrotriazine, formaldehyde, and methylamine. The kinetics of this reaction was studied by UV, GC, and HPLC as a function of temperature, initial concentrations of sodium hydroxide, and chlorinated derivative. The reaction is of the second order and obeys an E2 mechanism (k1 =4.2 × 10-5 M-1 s-1, ΔH# = 82 kJ mol-1, ΔS# = -59 J mol-1 K-1) The oxidation of unsymmetrical dimethylhydrazine by dimethylchloramine involves two consecutive processes. The first step follows a first-order law with respect to haloamine and hydrazine, leading to the formation of an aminonitrene intermediate (k2 = 150 × 10-5 M-1 s -1). The second step corresponds to the conversion of aminonitrene into formaldehyde dimethylhydrazone at pH 13). This reaction follows a first-order law (k3 = 23.5 × 10-5 s-1) The dimethylchloramine-ammonia interaction corresponds to a SN2 bimoiecular mechanism (k4 = 0.9 × 10-5 M-1 s -1, pH 13, and T =25°C). The kinetic model formulated on the basis of the above reactions shows that the formation of the hydrazine in an aqueous medium comes under strong competition from the dehydrohalogenation of dimethylchloramine and the oxidation of the hydrazine formed by the original chlorinated derivative. A global model that explains the mechanisms both in an anhydrous and in an aqueous medium was elaborated.
MODELISATION GENERALE DES PROCESSUS REACTIONNELS INTERVENANT AU COURS DE LA SYNTHESE DE LA DIMETHYLHYDRAZINE ASYMETRIQUE PAR LE PROCEDE RASCHIG. QUANTIFICATION DES PRODUITS DE DEGRADATION (HYDRAZONE). I. FORMULATION DU MODELE. VALIDITE EN MILIEU DILUE. INTERPRETATION
Delalu, H.,Marchand, A.
, p. 2149 - 2162 (2007/10/02)
A kinetic model of Unsymetrical dimethylhydrazine (UDMH) formation by Raschig process has been established.Its application range runs from pH = 8 to 14.64 (4 mol.l-1 NaOH).The synthesis is controlled by the acid-base dissociation equilibria : (NH2Cl NHCl- + H+; (CH3)2NH2(+) (CH3)2NH + H+; (CH3)2NHNH2+ (CH3)2NNH2 + H+) and by the following elementary reactions : -Dimethylhydrazine elaboration molecular (NH2Cl / (CH3)2NH) and ionic (NHCl- / (CH3)2NH) processes -Dimethylchloramine formation from NH2Cl and (CH3)2NH2+ -UDMH catalytic oxidation by NH2Cl and dimethyldiazene (CH3)2N+=N- intermediate formation -Diazene decomposition to yield formaldehyde dimethylhydrazone (FDMH) -Degradation of (CH3)2N+=N- by NH2Cl -Alkaline hydrolysis of chloramine.The synthesis can be expressed by a differential system of which the integration allows to foresee the evolution of mixtures in terms of concentration, pH and temperature.In particular, it allows a numeric evaluation of FDMH, troublesome by-product of the UDMH manufacture.Significant examples selected in different pH ranges and concentration have permitted to test the coherence between experimental and calculated curves.
