Oxygen exchange during the reaction of POCl₃ and water

To investigate O exchange during the reaction of POCl₃ and water, natural abundance POCl₃ was reacted with water highly enriched in ¹â¸O, and the resulting H₃POâ‚„ was isolated as KHâ‚‚POâ‚„. This reaction was conducted with and without tetrahydrofuran (THF) as a solvent, and was controlled in THF and violent in its absence. Approximately 5 x 10â»â´M aqueous solutions of the KHâ‚‚POâ‚„ were analyzed using electrospray ionization mass spectrometry, to estimate the proportions of the mass-clumped ¹ⶠ¹ⷠ¹â¸O isotope analogues of [Hâ‚‚POâ‚„]â». During analysis, ~29% of [Hâ‚‚POâ‚„]â» dehydrated to PO₃]â», for which the proportions of the O isotope analogues were also measured. These proportions were compared with those predicted for O exchange at either four or three positions on the P atom of POCl₃. The data strongly support O exchange at all four positions, whether or not THF was used to moderate conditions during the reaction. This result clears the way for safe, predictable synthesis of heavy-O labelled orthophosphate from POCl₃ and ¹â¸O enriched water for evaluation as an environmental and biochemical tracer.