Characterization of the UV spectrum and photolysis of chlorothalonil in the presence and absence of oxygen

COOKE, MARÍA VICTORIA; MARÍA BELÉN OVIEDO; PELÁEZ, WALTER JOSÉ; ARGÜELLO, GUSTAVO ALEJANDRO

Conferencia; 14th Latin American Conference on Physical Organic Chemistry.; 2017

Even though several photochemical studies have been conducted of chlorothalonil (CT), which is a non-systemic broad spectrum fungicide widely used in America, its UV spectrum has never been analyzed in detail.In this work we have analyzed the UV spectrum in different solvents and obtained the electronic transitions of the spectrum via TD-DFT calculations (B3LYP/6-31+G(d,p)), figure 1a (UV in ACN). We found that the experimental spectrum had more bands than the calculated one. For that reason the vibrionic spectrum for the first (Figure 1b) and second excited states where simulated with the Franck-Condon approximation (FC) using the methodology of Bloino and Barone. Also, the photolyses of CT in ACN in the presence and absence of oxygen at 254 nm were performed. The rate of decomposition of CT in the presence of O2 was about 30 times slower than with the same deoxygenated solution. We were able to determine the formation of 1O2 via energy transfer of CT* using an indirect approach, where cysteine is oxidized to cystine. We concluded that the presence of oxygen in the solution does not allow the CT degradation, which turns it more persistent in the environment as well as a great generator of 1O2, a possible precursor of tropospheric ozone.