The kinetics of a series of coordination reactions between rare earth metals and bisazochromotropic acid were studied. The common formula of rate law is r = k[RE(H2O)m3+] [H6R]b (H3O+)-1, where b = 1 or 2. Their Arrhenius activation energies are 40-70 kJ/mol. According to the composition of the transition state of the rate-detg. step from the rate law, 2 types of mechanism, i.e. the dehydration step of coordination complex and the proton transfer step, are proposed. The rate equation obtained from either mechanism is in conformity with the experimental rate law.

Key words: REACTION MECHANISM, REACTION KINETICS, IRON COMPLEX, KINETICS EQUATIONS, RARE EARTH METAL COMPLEX, CHLOROPHOSPHONAZO, LANTHANUM COMPLEX, GADOLINIUM COMPLEX, GADOLINIUM COMPLEX, ERBIUM COMPLEX