title: Kinetics and mechanism of cymoxanil degradation in buffer solutions.
abstract: The kinetics and mechanism(s) of the hydrolytic degradation of a compound are needed 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 conditions (pH 2.8-9.2) and temperatures (15-50 degrees C). 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 10 degrees C 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) (1, Figure 1) or direct cleavage of the C-1 amide bond to form cyano(methoxyimino) acetic acid (7). The third pathway of degradation involved initial cyclization to 3-ethyl-4-(methoxyimino)-2,5-dioxo-4-imidazolidinecarbonitrile (8), which rapidly degrades into 1-ethyl-5-(methoxyimino)-2,4-imidazoline-2,4-dione (9). All three pathways eventually lead to the formation of the polar metabolite oxalic acid.
authors.affiliation: Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli "Federico II", Napoli, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Morrica
authors.forename: Steven
authors.initials: S
authors.lastname: Trabue
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Anderson
authors.forename: Sonya
authors.initials: S
authors.lastname: Lawler
authors.forename: Serenella
authors.initials: S
authors.lastname: Seccia
authors.forename: Paola
authors.initials: P
authors.lastname: Fidente
authors.forename: R Scott
authors.initials: RS
authors.lastname: Swain
authors.forename: S Lynne
authors.initials: SL
authors.lastname: Mattson
mesh_terms: D000081:Acetamides / Q000737:chemistry*; D002021:Buffers; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005659:Fungicides, Industrial / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D019815:Oxalic Acid / Q000737:chemistry; D012996:Solutions; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000081:Acetamides; D002021:Buffers; D005659:Fungicides, Industrial; D012996:Solutions; C025644:2-cyano-N-((ethylamino)carbonyl)-2-(methoxyimino)acetamide; D019815:Oxalic Acid