Inorganic reactions of iodine(+1) in acidic solutions

We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H2OI+ reversible arrow HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3. Our new value, K(H2OI+ reversible arrow HOI + H+) similar to 2 M at 25degreesC, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI --> IO3- + 2I(-) + 3H(+) in perchloric acid solutions from 5 x 10(-2) M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M-1 s(-1) at 25 degreesC and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI reversible arrow I2O.H2O in the mechanism. (C) 2004 Wiley Periodicals, Inc.