text: Vinylphosphonic acid can be prepared by the reaction of PCl and acetaldehyde:
  :PCl + CHCHO → CHCH(O)
  This adduct reacts with acetic acid: 
  : CHCH(O) + 2 CHCOH → CHCH(Cl)PO(OH) + 2 CHCOCl
  This chloride undergoes dehydrochlorination to afford the target:
  :CHCH(Cl)PO(OH) → CH=CHPO(OH) + HCl
  In the Kinnear–Perren reaction alkylphosphonyl dichlorides and esters are generated by alkylation of phosphorus trichloride in the presence of aluminium trichloride.  Alkyltrichlorophosphonium salts are intermediates:
  :PCl  +  RCl  +  AlCl  →  RPCl + AlCl
  The RPCl product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl.