1995 Volume 44 Issue 12 Pages 1086-1092
A pseudo-first-order reaction constants (kobs) of dyes having a single hydroxyl group inthe molecule (Orange I, Orange II) by various bleaching agents were measured as a function ofpH. Used bleaching agents were hydrogen peroxide, peracetic acid, potassium permonosulfate, and sodium hypochlorite. The kobs of each dye showed maximum at intermediate pH betweenan acid dissociation constant of bleaching agent (pKa) and an acid dissociation constant of dye (pKd). Distribution curves of kobs on pH showed symmetrical narrow distribution when the value of pKd was close to pKa, and symmetrical broad distribution when the value of pKd was far apart from pKa. These results were analyzed with reaction kinetics by assumming the ionic reaction among protonated and deprotonated form of the bleaching agents and the dyes. It wasproved that the distribution curves of kobs on pH follow the following equation.
kobs= [A] t/ (1+ [H+] /Ka) (1+Kd/ [H+])
where [A] t is the total bleaching agent concentration, k1 is a second-order reaction constant byassuming the reaction between protonated dye ; [DyeH] and deprotonated bleaching agents ; [A-]. The calculated values obtained by above equation were in good agreement with the observed values. Therefore, it was concluded that the decoloration mechanism of the dyes by bleaching agents conforms to the ionic reaction among protonated and deprotonated forms of the bleaching agents and the dyes. We have named this decoloration mechanism as “the mutual ionic reaction mechanism”.