(2-Mercaptophenyl)phosphonic acid is prepared by hydrolysis of dialkyl
(2-mercaptophenyl)phosphonate, which is itself formed either by react
ion of dialkyl chlorophosphate with lithium 2-lithiobenzenethiolate, o
r from the lithiated derivative of the readily prepared O,O-diisopropy
l S-phenyl thiophosphate whose phosphoryl group then undergoes an S --
> C migration.