PROMETRYNE OXIDATION BY SODIUM-HYPOCHLORITE ITS AQUEOUS-SOLUTION - KINETICS AND MECHANISM

The reaction of the herbicide prometryne (C9H16N5-S-CH3) with sodium h ypochlorite has been investigated from the kinetic and mechanistic sta nd point. Under the fixed experimental conditions: pH = 7, T = 25 degr ees C, [NaClO]/[substrate] = (10(-3) M)/(10(-5) M), prometryne oxidati on takes place according to the following pathway: R-S-CH3 (P) --> R-S O-CH3 (a) --> R-SO2-CH3 (b) --> R-O-SO2-CH3 (x) --> R-OH (c), where R stands for C9H16N5, i.e., the substituted triazine ring of prometryne and (x) is an unexpected intermediate never previously detected nor id entified. After having synthesized the pure intermediates (a), (b), an d (x), the values of the pseudo-first-order kinetic constants of the f irst three steps were experimentally obtained: [k(1) = (0.64 +/- 0.03) s(-1), k(2) = (1.81 +/- 0.05) x 10(-3) S-1 k(3) = (1.50 +/- 0.03) x 1 0(-4) s(-1)]. As for k(4), its value [(2.5 +/- 0.2) x 10(-5) s(-1)] ha s been calculated indirectly on the basis of the kinetic theory concer ning consecutive reactions. All the steps were pseudo-first-order reac tions with respect to their specific substrate. The effect of pH on th e hydrolysis of (b) [(b) --> (c)], in the absence of NaClO, has been a lso assessed to better elucidate the mechanism of the overall pathway.