Efficient Methanolytic Cleavage of Phosphate, Phosphonate, and Phosphonothioate Esters Promoted by Solid Supported Lanthanide Ions

The methanolyses of three neutral organophosphorus esters, namely paraoxon (O,O-diethyl O-p-nitrophenyl phosphate (12), O-ethyl O-p-nitrophenyl methylphosphonate (13), O-ethyl S-3,5-dichlorophenyl methylphosphonothioate (14, a model for VX), and an anionic phosphonate ester, O-hydrogen S-3,5-dichlorophenyl methylphosphonothioate (15, a model for a toxic hydrolytic decomposition product of VX known as EA2192)), promoted by solid supported lanthanide ion catalysts (La3+, Sm3+, Eu3+, Yb3+) were investigated at 25 °C under s spH controlled conditions in methanol. The supports were derived from commercially available chlorobenzylated silica and chloromethylated polystyrene functionalized with two chelating ligands, iminodiacetic acid (IDA) and ethylenediamine-N,N′-diacetic acid (EDDA), followed by exposure to Ln3+ ions. The catalysts showed good activity at two investigated s spH values of 8.8 and 11 (in methanol). Despite the fact that the methoxide promoted reactions for the four substrates span a range of ∼20 000-fold, the apparent second order rate constants (k 2 app) for methanolysis of these promoted by the solid supported lanthanide catalysts were rather insensitive to the nature of the support (Si or polystyrene), Ln3+ ion, substrate, and s spH. The Yb3+ complex of IDA on silica (Si/IDA/Yb) gave the highest k 2 app values of 6.6 and 14.4 M−1 s−1 for 12 and 13, 48.8 M−1 s−1 for 14, and 2.6 M−1 s−1 for 15 at s spH 11. The acceleration of cleavage of 13 at s spH 8.8 by the Si/IDA/Yb catalyst at an apparent concentration of 4.8 mM (50 mg suspended in 2.5 mL of methanol) is about 8.5 × 105 faster than the methoxide reaction at that s spH. The acceleration of the cleavage of 14 and 15 by 50 mg of Si/IDA/Yb at s spH 11 is 6.3 × 105- and 5 × 108-fold relative to the methoxide promoted reaction at that s spH. The matrixes containing the smaller lanthanide ions like Eu and Yb could be recycled at least eight times without loss of activity.