Atmospheric reactivity of pentagonal heterocyclic compounds. Reaction with nitrate radicals (Spanish text)

The Atmospheric Chemistry is determined mainly by some degradation processes, such as photolysis or oxidation reactions. In the last case, three species play a key role in atmospheric processes: nitrate radical (NO ₃), hydroxyl radical (OH) and ozone (O₃). In this way, the most of organic compounds emitted to the atmosphere are chemically removed by day-time reaction with OH radical and by reaction with NO₃ radical at night-time.; Between these compounds emitted to the atmosphere, pentagonal heterocyclic compounds are important pollutants. So, thiophene, furan and pyrrole have been detected in ambient air of some cities, as a consequence of processes related with the energy production such as coal gasification, natural gas, coal combustion, etc. The heterocyclic compounds are not only important per se, but also as model compounds for other larger molecules such as PACs and dioxins.; In this sense, a systematic investigation of the reactions between the nitrate radical and heterocyclic compounds has been performed in this thesis. The kinetic behaviour and products of these reactions has been studied using two different techniques. First, studies of the absolute rate constants at different temperatures and of the products of reaction at low pressures have been performed in a fast flow system using laser induced fluorescence (L.I.F.) and mass spectrometry as detection systems. Secondly, the relative rate constants at room temperature and products at atmospheric pressure have been determined using a static system with a Teflon bag as reactor and GC-MS and GC-FID as detection techniques.; Similar values for the rate constants obtained in both systems indicate that these reactions do not show pressure dependence. Thus, the results at low pressures can be extrapolated to atmospheric conditions. Moreover, both the kinetic results and products studies indicate that different reaction mechanism are operating in these reactions depending on the nature of the heteroatom and substituents in the cycle.; In general, for derivates of thiophene, SO₂ and unsaturated dicarbonyl compounds are the main products. For furan, an unsaturated dicarbonyl compound is formed. In the case of THF and THT, HNO₃ and two organic sulphuric compounds have been detected as reaction products, respectively.