Mercuric chloride-catalyzed hydrolysis of the new antifouling compound Irgarol 1051

Irgarol 1051, 2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine, is a newly developed herbicidal additive for use in copper-based antifouli ng paints. It is intended to replace the antifouling agent tributyltin, whi ch has been regulated internationally due to its severe impact on the aquat ic ecosystem. However, there is no information in the open literature on th e abiotic degradation of Irgarol, a fact that hinders the assessment of its ultimate impact on the environment. This study showed that mercuric chlori de was capable of rapidly catalyzing the hydrolysis of Irgarol 1051 in dist illed water and buffer solutions. The degradation appeared to follow the re action of a catalyzed hydrolysis and was not significantly affected by the pH tested (5 to 9). All other 5 heavy metal salts tested (AgNO3, CdCl2, CuS O4, PbCl2 and ZnCl2) had practically no catalytic property on Irgarol hydro lysis, implying the involvement of a specific activity for Hg2+ in this rea ction. The mechanism for the catalyzed hydrolysis may be the formation of b identate chelation through nitrogen: (No. 5) on the ring and the nitrogen o n the cyclopropyl-amino side chain in Irgarol 1051 with the Hg2+ ion. The r esulting four member chelate complex would weaken the cyclopropyl-amino bon d considerably, thus facilitating the hydrolysis reaction. Ultraviolet spec troscopy of the reaction mixtures and the identification of Irgarol hydroly sis product M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) by GC-MS and LC-MS provided the basis for the proposed mechanism on the HgCl2-catal yzed hydrolysis of Irgarol 1051. M1 appeared to be more stable than the par ent compound Irgarol 1051, thus implying its possible accumulation in the e nvironment. One practical aspect of this work is that HgCl2 should not be u sed in preserving water samples in Irgarol 1051 monitoring programs. (C) 19 98 Elsevier Science Ltd. All rights reserved.