|Swain, R. Scott|
|Mattson, S. Lynn|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2003
Publication Date: 1/1/2004
Citation: Morrica, P., Trabue, S.L., Anderson, J.J., Lawler, S., Seccia, S., Fidente, P., Swain, R., Mattson, S. 2004. Kinetics and mechanism of cymoxanil degradation in buffer solutions. Journal of Agricultural and Food Chemistry. 52:99-104. Interpretive Summary: Cymoxanil-based fungicides have been in use for over 25 years and are used to control fungal pathogens some of which were responsible for the Irish potato famine. Despite cymoxanil's long history of use, there is still little to no data on its environmental characteristics. In this study, the rate of cymoxanil degradation and its degradation products formed during hydrolysis was monitored as a function of pH and temperature. Hydrolysis of cymoxanil was rapid under alkaline conditions (pH = 9, half-life 31 min.) as compared to acidic conditions (pH 2.8, half-life = 722 days). The effect of temperature was also pronounced with an estimated five fold change in the degradation rate for each 10oC temperature change. Cymoxanil hydrolytic degradation was different than its degradation in either animal or plants. Information from this study will provide researchers data to be used in modeling the fate of cymoxanil in the environment and provide structures of compounds to be tested for potential toxicological properties.
Technical Abstract: The kinetics and mechanism(s) of hydrolytic degradation of a compound are needed in order to evaluate a compound's abiotic degradation in the environment. In this paper, the hydrolysis of cymoxanil (2-cyano-N-[(ethylamino)carbonyl]-2-(methoxyimino) acetamide) was investigated in dark sterile aqueous solutions under a variety of pH buffers (pH 2.8 to 9.2) and temperatures (15 to 50oC). Hydrolysis of cymoxanil was described by first order kinetics, which was dependent on pH and temperature. Cymoxanil degraded rapidly at pH 9 (half-life = 31 min.) and relatively slowly at pH 2.8 (half-life = 722 days). The effect of temperature on the rate of cymoxanil degradation was characterized using the Arrhenius equation with an estimated energy of activation of 117.1 kJ mol-1. An increase in temperature of 10oC resulted in a decrease in half-life by a factor of approximately 5. Three competing degradation pathways are proposed for the hydrolysis of cymoxanil with two of the pathways accounting for approximately 90% of cymoxanil degradation. These two pathways involved either initial cyclization to 1 ethyldihydro-6-imino-2,3,5(3H)-pyrimidinetrione-5 -(O-methyloxime), or direct cleavage of the C-1 amide bond to form cyano(methoxyimino) acetic acid. The third pathway of degradation involved initial cyclization to 3-ethyl-4-(methoxyimino)-2,5-dioxo-4-imidazolidinecarbonitrile, which rapidly degrades into 1-ethyl-5-(methoxyimino)-2,4-imidazolin-2,4-dione. All three pathways eventually lead to the formation of the polar metabolite oxalic acid.