Conant-Swan reaction

The presence of one or more halogen atoms on a carbon atom a or j to P=0 renders the phosphorus-carbon bond more liable to break under less forcing circumstances. The fragmentation of (2-haloalkyl)phosphonic acids under aqueous conditions (the Conant-Swan reaction) has been known for many years. Conant and coworkers" ", in the early 1920s, reported on the instantaneous fragmentation of the acids 88 and 89 in aqueous NaHCOj into inorganic phosphate, Br and PhCOCH=CHPh. 

Polymers were used to test the intermediacy of a phosphorylated compound in phosphorylations observed during base-promoted decomposition of /3-halo phosphonate (Conant-Swan reaction) (Rebek et al., 1977,1978). Polymer-bound jS-chlorophosphonate was prepared and decomposed in the presence of an amine-bearing polymer of different bead size. It was shown that phosphorylation of the amine-bearing polymer occurred, indicating the intermediacy in solution of a phosphorylating species. 

Satterthwait also has demonstrated that methyl metaphosphate, generated in solution by the Conant-Swan fragmentation, will react with acetophenone in the presence of base to yield the corresponding enol phosphate. When, however, the reaction is carried out in the presence of aniline, the product is the Schiff base. Presumably, the processes take place by the pathways shown by the reactions in Equations 10 and 11. 

Knowles and co-workers have studied the stereochemical consequences of the presumed S>jl(P) reaction. They have shown that the methanolysis of chiral 0 0 0-substituted phenol- and 2,4-dinitrophenylphosphate and phosphocreatine (13, 14), under conditions where they were expected to react by the metaphosphate pathway, all undergo complete inversion of configuration at phosphorus. This result implies that the putative metaphosphate is not a free intermediate that it is not even long-lived enough to equilibrate with the solvent cage in which it is formed. It was concluded that the reaction must be preassociative at least in aqueous-alcoholic media. A recent report (24) has shown that the Conant-Swan fragmentation described earlier also occurs with inversion about the phosphorus atom. 

Dimethyl methylphosphonate can be used as a methylating agent (6.279). In aqueous alkaline solutions, p-halophosphonates are decomposed with rupture of the P-C bond (Conant-Swan fragmentation) (6.280) [23]. This reaction is believed to involve the monometaphosphate anion as an intermediate species (13.147). 

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