The reaction between periodate and thiourea in acidic medium has been investigated in a batch. The stoichiometries of the reaction are: 4IO_4~- + SC(NH_2)_2 + 3H_2O = 4IO_3~- + SO_4~(2-) + CO_3~(2-) + 2H~+ + 2NH_4~+ ([IO_4~-]/[SC(NH_2)_2]_0 > 4) (1) 8IO_4~- + 7SC(NH_2)_2 + 17H_2O = 4I_2 + 7SO_4~(2-) + 7CO_3~(2-) + 6H~+ + 14NH_4~+ ([IO_4~-]/ [SC(NH_2)_2] ≈ 8:7) and mixed reaction of (l) and (2) (8/7 < [IO_4~-]/ [SC(NH_2)_2]< 4 ), respectively. In closed systems the reaction is autocatalytic in H+ and I" , and can be characterized by two different induction periods. In excessive periodate, the induction period defined as the time between the beginning of reaction and the appearance of a red-brown colour, indicating the product of iodine, has a linear relation with 1/[H~+ ]~2. In excessive thiourea, the induction period from the start of reaction to maximal [l2] is directly proportional to the initial pH. A fifteen-step mechanism, including iodine-iodine reactions, iodine-sulfur reactions and sulfur- sulfur reactions, simulated the observed kinetics.

Key words: OSCILLATION CHEMICAL REACTION, PERIODATE, THIOUREAS, OXIDATION, REACTION KINETICS, REACTION MECHANISM