Physical Chemistry, Poster
Complex thermolysis mechanism of phosphoramidate: Formation of PN based gas phase active phosphorus species
S. Liang1,5, P. Hemberger2, J. Levalois-Grützmacher3, O. Korobeinichev4, H. Grützmacher3*, S. Gaan6*
1ETH Zürich, 2Paul Scherrer Institute, Villigen, 3ETH Zurich, 4Siberian Branch Russian Academy of Sciences Russia, 5Empa, 6EMPA St. Gallen
P-N containing organophosphorus compounds have received increasing attention in different domains, such as biology, catalysis and in particular as flame retardant additives [1]. However, due to the complexity of the flame chemistry and the lack of proper analytical technique allowing for simultaneous snapshots of the thermolysis process under different conditions, their corresponding inhibition mechanism in the flame still remains open. This study aims to make a valuable contribution towards a better understanding of decomposition mechanism of the yet unstudied phosphoramidate category and thereby provides a foundation for the targeted design of new molecules. Taking advantage of the tunability of VUV synchrotron radiation, the thermolysis process of dimethyl phosphoramidate was elucidated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy, which allows for isomer-resolved species identification, by recording temperature dependent mass spectra as well as threshold photoelectron spectra (TPES) for each relevant species (Fig. 1 (a)). To correlate the probed decomposition mechanism of DMPR with the corresponding inhibition efficiency under fire conditions, we performed further experiments with a laminar premixed methane-air flame, in which the formation of H and OH responsible for maintaining flames was monitored using a molecular beam mass spectrometry (MBMS, Fig. 1 (b)) [2].
Based on these synchrotron experiments, a number of species such as methanimine, ethylene and different phosphoryl species were unequivocally identified, including the commonly known PO, OPOH [3] as well as the yet unknown species PN. More interestingly, the signal intensity in the MS proves a significant preference on PN formation than other phosphoryl species. Different computational chemistry approaches have been applied to develop a comprehensive reaction mechanism, while the most dominant pathways will be presented and discussed. Besides, by further investigating the efficiency of radical inhibition in flame sampling MBMS experiments, the promising roles of PN in poisoning the flame will be addressed.
[1] a) M. Derudas, et al., Bioorganic Medicinal Chemistry 2010, 18, 2748-55; b) P. Garcia, et al., Angewandte Chemie International Edition 2013, 52, 9144-8; c) S. Gaan, et al., Polymer Degradation and Stability 2009, 94, 1125-34; d) T.M. Nguyen, et al., Industrial Engineering Chemistry Research 2013, 52, 4715-24.
[2] N. Hansen, et al., Progress in Energy and Combustion Science 2009, 35, 168-91.
[3] S. Liang, et al., Chemistry – A European Journal 2015, 21, 1073-80.