Most processes begin with phosphorous acid (aka phosphonic acid, HPO), exploiting its reactive P−H bond.
Phosphonic acid can be alkylated via the Kabachnik–Fields reaction or Pudovik reaction to give aminophosphonate, which are useful as chelating agents. One example is the industrial preparation of nitrilotris(methylenephosphonic acid):
:NH + 3 HPO + 3 CHO → N(CHPOH) + 3 HO
Phosphonic acid also can be alkylated with acrylic acid derivatives to afford carboxyl functionalized phosphonic acids. This reaction is a variant of the Michael addition:
:CH=CHCOR + 3 HPO → (HO)P(O)CHCHCOR
In the Hirao coupling dialkyl phosphites (which can also be viewed as di-esters of phosphonic acid: (O=PH(OR)) undergo a palladium-catalyzed coupling reaction with an aryl halide to form a phosphonate.