Natural Abiotic Formation of Furans in Soil

Furan and its derivates are a potentially important and little studied, class of volatile organic compounds of relevance to atmospheric chemistry. The emission of these reactive compounds has been attributed previously to biomass burning processes and biogenic sources. This paper investigates the natural abiotic formation of furans in soils, induced by the oxidation of organic matter by iron(III) and hydrogen peroxide. Several model compounds like catechol, substituted catechols, and phenols as well as different organic-rich soil samples were investigated for the release of furans. The measurements were performed with a purge and trap GC/MS system and the influence of hydrogen peroxide, reaction temperature, iron(III), pH, and reaction time on furan yield was determined. The optimal reaction turnover obtained with catechol was 2.33 mu g of furan from 0.36 mg of carbon. Results presented in this paper show that a cleavage of catechol into a C-2- and a C-4-fragment occurs, in which the C-4-fragment forms furan by integrating an oxygen atom stemming from H2O2. Furthermore, phenols could be transformed into catecholic structures under these Fenton-like conditions and also display the formation of furans. In conclusion, catalytic amounts of iron(III), the presence of hydrogen peroxide, and acidic conditions can be seen as the most important parameters required for an optimized furan formation.