Thermal reactions of N-methylmorpholine-N-oxide (NMMO): A general method for separation and quantification of N-methylmorpholine-N-oxide and its maindegradation products N-methylmorpholine and morpholine by capillary electrophoresis (CE)

A general analytical method based on capillary electrophoresis with indirec t UV detection has been developed to separate and quantify N-methylmorpholi ne-N-oxide (NMO) and its main degradation products N-methylmorpholine (NMM) and morpholine (M). The electrolyte is based on the two major components 4 -methylbenzylamine and 2-hydroxy-2-methylpropanoic acid (hydroxy-isobutyric acid, HIBA), the latter being used to adjust the pH to a value below 3.5 w hich is crucial for the electrophoretic mobility and, thus, for a good dete ctability of the amine oxide. The present method is widely applicable to mo nitor kinetics of reaction mixtures containing NMMO. NMM and M can be deter mined simultaneously even in a 1000-fold excess of NMMO. To monitor the fast and exothermic thermal degradation of NMMO by the elect rophoretic method, special reaction conditions had to be developed for sepa rating the initial decomposition step from super imposed subsequent reactio ns. Reactive degradation products were removed by flushing with nitrogen, a nd the reaction rate was decreased by dilution with o-dichlorobenzene as an inert solvent. The initial phase of the decomposition reaction has been sh own to follow second-order kinetics.