Dicloran appears to be a model pesticide for investigating photodegradation processes in surface waters. Photodegradation processes are particularly relevant to this compound as it is applied to crops grown in proximity to freshwater and marine ecosystems. The photodegradation of dicloran under simulated sunlight was measured in distilled water, artificial seawater, phosphate buffer, and filter-sterilized estuarine water to determine its half-life, degradation rate, and photodegradation products. The half-life was approximately 7.5 h in all media. There was no significant difference in the rate of degradation between distilled water and artificial seawater for dicloran. For the intermediate products, a higher concentration of 2-chloro-1,4-benzoquinone was measured in artificial seawater versus distilled water, while a slightly higher concentration of 1,4-benzoquinone was measured in distilled water versus artificial seawater. The detection of chloride and nitrate ions after 2 h of light exposure suggests photonucleophilic substitution contributes to the degradation process. Differences in product distributions between water types suggest that salinity impacts on chemical degradation may need to be addressed in chemical exposure assessments.
In this experiment for an upper-division course in organic structure
determination, each student prepares an unknown compound and characterizes
the product using multiple spectroscopic techniques. The unknowns,
2-aryl-substituted 1,4-dihydro-3,1-benzoxazines and 1,2,3,4-tetrahydroquinazolines,
are prepared in a single step by the condensation of commercially
available aryl aldehydes with 2-aminobenzyl alcohol or 2-aminobenzylamine,
respectively. The products are purified by recrystallization and characterized
by their mass, IR, 1H NMR, 13C NMR, COSY, and
HMQC spectra. Pre- and postlab assignments encourage students to use
both mechanistic reasoning and information from multiple spectroscopic
techniques for structure elucidation.
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