White phosphorus is a very efficient trap for carbon radicals generated by white light photolysis of Barton PTOC esters using CH2Cl2-CS2 as solvent at 0 Deg under dry argon. Removal of the solvent mixt. and oxidn. with H2O2 in 1,2-dimethoxyethane provides an efficient new synthesis of phosphonic acids, where this function replaces the carboxyl in the original carboxylic acid. [on SciFinder (R)]