Elucidation of the photodegradation mechanism of CCl3C(O)NH2, CClF2C(O)NH2 and CF3C(O)NH2 in solid state (266 nm) and solution (254 nm). Experimental and theoretical studies.

Abstract

In this work we present the study of the direct photolysis processes for 2,2,2-trichloroacetamide (TCA), 2-chloro-2, 2-difluoroacetamide (CDFA) and 2,2,2-trifluoroacetamide (TFA), in solid state and solution. CH3OH, CH3CN and H2O were used as solvents, and the irradiation (254 nm) was carried out in oxygen enriched as well as in oxygen free (N2 bubbled) solutions. The 266 nm light was reserved for the solid samples. In solution, the process was followed by UV–vis spectroscopy and the products analyzed by gas chromatography coupled to mass spectrometry (GC[sbnd]MS); while the gas phase products from the solid photodegradation processes, were followed by FTIR spectroscopy. The main electronic transitions were assigned on the bases of chemical calculations, and they do corroborate the proposed mechanisms. For both TCA and CDFA, the breakdown of the C-Cl bond is observed as the major process, with an activation energy of around 42 kcal/mol (in solution) and 27 kcal/mol (in gas phase), and a quantum yield of 0.01. TFA does not degrade under these experimental conditions.