Some new observations on an old reaction: disproportionation and the formation of P-O-P intermediates in the Michaelis-Arbuzov reaction of triaryl phosphites with alkyl halides

Thermolysis of methyltriaryloxyphosphonium halides (ArO)3PMeX (X = Br or I) in the molten state (> 175 C) was accompanied by disproportionation, with the formation of structures of the general type (ArO)nPMe4-nX (X = Br or I; n = 0-4). Further decomposition to give the corresponding aryl halides and phosphoryl derivatives became progressively slower as aryloxy groups were replaced by methyl. Thermal decomposition in CDCl3 (sealed tube) additionally confirmed the formation of novel species containing a P-O-P linkage. Products were identified by a combination of P and H NMR spectroscopy. Possible reaction mechanisms are discussed.