Hypophosphite and thallic perchlorate react in aqueous perchloric acid solution as follows: Tl^III+ H₃PO₂+ H₂O = Tl^I+ H₃PO₃+ 2H⁺ Hydrogen ion has no effect on the rate. The empirical rate law is: –d[Tl^III]//_dt=k[Tl^III][H₃PO₂]//_{1 +K1[H3PO2]} Complex formation between TI^III and H₃PO₂ is suggested. Chloride ion increases the rate by forming a more reactive complex.