Alkaline hydrolysis of bisphosphonium salts with fragmentation Ep mechanism

The duality of approach, on the one hand, and the combination of the resulting compounds, unique in the basic hydrolysis of phosphonium salts, on the other, lead to this reaction being said to occur by an p mechanism , described in a separate section. 

TABLE 20. Alkaline hydrolysis of 1,2-ethylene- or 1,2-vinylenebisphosphonium salts 

The ease of decomposition according to the Ep mechanism was explained by Brophy and Gallagher657 on the basis of an intermediate conformation particularly in favour of the elimination reaction  

Finally, it should be noted that other vinylogue structures such as 40 and 41 decompose 

Another kind of bridge between two phosphonio groups corresponding to the P +—C—C—O—C—C—P+ chain, is favourable to the same type of Ep fragmentation (reaction 189)353. Here the leaving group fragmentation is probably favoured by the interaction nQ- P +.  

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