The kinetics of alkaline hydrolysis of the cyclic phosphonium salts, 9,9-dimethyl-9-phosphoniafluorene iodide (V; R Me) and 10,10-dimethylphenoxaphosphonium iodide (VIII; R Me) which proceed with cleavage of the ring system, have been studied at different temperatures in 50% aqueous ethanol; both reactions follow a third-order rate law. The five-membered fused ring phosphoniafluorene salt (V; R Me) undergoes hydrolysis twice as rapidly as the six-membered fused ring phenoxaphosphonium salt (VIII; R Me). Under the conditions used for the hydrolysis of these salts, dimethyldiphenylphosphonium iodide did not hydrolyse to an apprecible extent.

The rate data and activation parameters for the above reactions are compared with the data for other cyclic phosphonium salts.