Mass spectometric studies on cyclo- and poly-phosphazenes. Part 5. Oligomerization of octachlorocyclotetraphosphazatetraene N4P4Cl8

Abstract

The electron impact (e.i.) mass spectrometric behaviour of N₄P₄Cl₈ shows that the main reaction process involves the formation of a heptachlorocyclophosphazene phosphorus cation [N₄P₄Cl₇]⁺, which has a cyclotriphosphazatriene ring bearing a NPCl₂ side group. This collapse of the cyclotetraphosphazatetraene structure to a cyclotriphosphazatriene moiety is a consequence of a ring-contraction reaction which yields more stable ionic trimeric phosphazene species. Ions [N₃P₃Cl₅]⁺ are subsequently formed by the loss of the NPCl₂ unit. Upon increasing the N₄P₄Cl₈ vapour pressure to 0.65 Torr in the ionization chamber of the mass spectrometer, an oligomerization process takes place leading to chlorophosphazene oligomers, with oligomerization degree n of 12. Evidence is presented to show that the tetrameric ions [N₄P₄Cl₈]˙⁺ formed from N₄P₈Cl₈ under e.i. conditions have a different structure compared to analogous species produced during the gas-phase polymerization process of N₃P₃Cl₆. This result gives further support to the mechanism proposed for gas-phase oligomerization of N₃P₃Cl₆.