STUDIES ON BETA-TYPE REACTION AND KINETICS OF LANTHANIDES WITH P-BROMOCHLOROARSENAZO

The reaction behaviour of the beta-type chelates of lanthanide ions (L n(3+)) with p-bromochloroarsenazo (4-CAsA-pB) in 0.01 mol l(-1) HClO4, solution has been studied systematically by a spectrophotometric meth od. All the lanthanide ions can form beta-type chelates with p-bromoch loroarsenazo. The maximum absorption wavelength is in the range 727-73 1 nm, the molar absorptivities are about 6.0 x 10(4)-9.0 x 10(4) cm(2) mol(-1), the composition ratio of Ln(3+) ions with 4-CAsA-pB is 1:2 a nd the actual combining ratio is 2:4. The optimum acidity range (Delta pH value) of the formation of beta-type chelates has been obtained. K inetic parameters, such as the reaction order and rate constants, have also been studied and a formation mechanism for the beta-type chelate s has been proposed.