Comparative analysis of the photochemical processes of CH3C(O)NH2,CCl3C(O)NH2, CClF2C(O)NH2, and CF3C(O)NH2

ANA G. IRIARTE; GUSTAVO A. ARGÜELLO; RODRIGO DOMÍNGUEZ

Mendoza

Encuentro; 9th International Meeting on Photodynamics and related aspects.; 2016

International Meeting

Introduction: Since the earliest decades of the twenty century, acetamide and some of its trihalo-derivative compounds have gained importance due to their close relationship with the structure of proteins, which became them useful as model for the study of the peptide bond. Within this frame, formamide is one of the more studied compound both experimentally and theoretically, put the attention on the planarity of the NH2 moiety, the energies implied on the miscibility, internal rotational barrier around the C-N bond, force fields and structural and vibrational data. Besides, in order to get a deeper insight into the conformation of polypeptides and proteins, it was carried outmany theoretical studies about acetamide. Thus, studies concerning the peptide bond were performed not only with acetamide but also with their trihalo-substituted compounds, i.e. trichloro-, trifluoro- and chlorodifluor-acetamide.Objectives: Study the photolysis processes of acetamide (AC), 2,2,2-trichloroacetamide (TCA), 2,2,2-trifluoroacetamide (TFA) and 2-fluoro-2,2-dichloroacetamide (CDFA) in different systems, followed by UV-Vis spectroscopy. CH3OH, CH3CN and H2O were used as solvents, with and without O2 and N2 gas added and in degassed solvents. Determine photolysis rates for each of the systems and measure the quantum yields of the photodegradation of these compounds using the Parker´s actinometer. All the products were analysed by CG-Mass spectrometry. Propose possible reaction mechanisms depending on the products obtained.Results At 254nm, values cross sections of each compound in water, acetonitrile and methanol are the order of 10-20cm2/particle. We observed that FTA and AC were not changing their UV-Vis spectra during one hours of continuous photolysis at 254nm. CH3CO and NH2 radicals were produced by photolysis of AC in water35 and we were checked that same products in methanol and acetonitrile. These products absorb less than 200nm, so this process was followed by IR. For TFA are not products of photolysis observed at 254 nm. This result is consistent with expectations, because the incident energy is not enough to break their bonds. For TCA and CDFA the primary process involved the loss of a ·Cl with values photolysis constants of 10-5 s-1 in all solvents tested. The quantum yield was determined by chemical actinometry, using Parker´s actinometer. Their valueswere determined in three solvents measured. Conclusions: The degradation behaviour is observed differently according halogenated substituents involved. We checked the stability of C-X bonds (X=F y Cl) and we propose major degradation mechanisms. Solvents does not affect the process significantly, neither exist some thermal contribution to the photodegradation process between 20-65 ° C.