Kinetics and mechanisms of hydrolysis of dicarboximide fungicides in micellar media

The kinetics of alkaline hydrolysis of the dicarboximide fungicides procymidone, iprodione, vinclozolin, and chlozolinate (1-4, respectively) were investigated in micellar solutions containing various amounts of either sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), or three nonionic surfactants (two C-13 alcohols and a copra amine combined with ethoxyl chains) and compared with the kinetics in aqueous media. For all compounds, the rate constants observed are slightly reduced by the SDS micellar media, showing that reactions essentially take place in the aqueous pseudophase. The CTAB micellar media speed up the hydrolysis rates with small quantities of Br- ions in the medium. As the number of Br- ions increases, the rate of reactions falls. This is characteristic of an ion exchange (OH- and Br-) at the surface of the CTAB micelles. Finally, the presence of nonionic micelles has little influence on the hydrolysis of the fungicides: the reduction in the rate of dicarboximide ring opening is attributed to micelle-substrate association. These results can be explained by means of the pseudophase kinetic model coupled with the mechanisms of hydrolysis of these fungicides in water solution.