THE INVENTION OF RADICAL REACTIONS - PART 39 - THE REACTION OF WHITE PHOSPHORUS WITH CARBON-CENTERED RADICALS - AN IMPROVED PROCEDURE FOR THE SYNTHESIS OF PHOSPHONIC-ACIDS AND FURTHER MECHANISTIC INSIGHTS

White phosphorus in tetrahydrofuran under argon reacts in a long radic al chain reaction with carbon radicals derived from Barton PTOC esters . The reaction is initialed by traces of oxygen and strongly inhibited by TEMPO. From the duration of the induction period the chain length can be measured as approximately one million. Each P-4 molecule can ad d up to two carbon radicals. Oxidation of the adducts provides a conve nient synthesis of phosphonic acids in high yield. With H2O2 at 0 degr ees C oxidation to the appropriate phosphinic acids is fast. For sensi tive natural products the further transformation to phosphonic acids i s best carried out at room temperature with an excess of SO2. In this way even linoleic acid can be converted to the corresponding phosphoni c acid in good yield without any attack on the skipped diene unit. TEM PO is also remarkable for its stabilization of white phosphorus in sol ution when exposed to oxygen. Likewise an ordinary phosphine, like tri butyl phosphine, is also stabilized by small amounts of TEMPO. (C) 199 8 Published by Elsevier Science Ltd. All rights reserved.