PEROXYHYDROLYSIS OF NERVE-AGENT-VX AND MODEL COMPOUNDS AND RELATED NUCLEOPHILIC REACTIONS

The exceedingly toxic agent VX [O-ethyl S-(diisopropylaminoethyl) meth ylphosphonothioate], 1a, and the midly toxic model compound, O,S-dieth yl methylphosphonothioate, Ib, react with HO- to give parallel P-S and P-O bond cleavages; the P-O cleavage of VX produces relatively unreac tive but very toxic anionic phosphonothioate. Peroxyhydrolysis of 1a,b with HO2- involves quantitative P-S cleavage at rates 30-40 times tha t with HO- giving the corresponding phosphonate and sulfonate ions and disulfide as nontoxic products, In reaction of 1b with HO2- in H-2 O- 18, oxygen in these final products is not derived from water and HO2- exclusively displaces the thiolate ion at phosphorus, Reaction of Ib w ith HSO5- gives the same products, but via oxidatively promoted attack of H-2 O-18 on phosphorus; Kinetic and isotopic labelling results on reactions of la,b and a range of related compounds with HO2-, HO- and RO(-) and an oximate ion are interpreted in terms of concerted S(N)2(P ) reactions rather than stepwise reactions with formation of a trigona l bipyramidal (TBP) intermediate. Product selectivity depends on the r elative basicities of the anionic nucleophile and the leaving anions.