Self-oscillating reaction in the furan series

Abstract

It was found for the first time that the acid hydrolysis of 2,5-dimethylfuran in water-ethanol solutions has self-oscillating character. Oscillations in the concentrations of the two products 2,5-hexanedione and an unidentified compound X were detected by GLC. The ranges of hydrochloric acid and ethanol concentrations in which these oscillations appear were determined. It is suggested that the formation of compound X results from tautomeric transformations of 2,5-hexanedione under the reaction conditions. Quantum-chemical calculations showed that the possible tautomers are formed with equal probability.During the development of a method for the production of thiophenes and selenophenes by the recyclization of furans in water-ethanol media under the conditions of acid catalysis it was shown that the reaction takes place in two directions, one of which includes a stage involving the formation of a diketone, i.e., hydrolysis. Kinetic investigations of the hydrolysis of 2,5-dimethylfuran (1) in 50% ethanol under the influence of HCl revealed the formation of 2,5-hexanedione (2) and an unidentified compound X. During the reaction the ratio of the concentrations of the products varied with some degree of periodicity, i.e., as it accumulated one product changed into the other, and these transformations were self-oscillating in nature [1,2].Study of the behavior of furan compounds in aqueous and water-alcohol media under the conditions of acid catalysis is of great theoretical and practical interest in so far as oscillating chemical reactions take place in various types of processes that determine the vital activity of living organisms [3], while furan derivatives are physiologically active substances.In the present work in order to determine the boundary conditions for the appearance of the abovementioned transformations the kinetics of the hydrolysis of dimethylfuran 1 in 50% aqueous ethanol with various hydrochloric acid concentrations (1.5, 2.0, 3.0, 3.5 N) were investigated by GLC. The results of the experiments are presented in Fig. 1. As seen, the fluctuations in the contents of the dione 2 and compound X in the reaction medium are observed at HCl concentrations (c) of 1.5-2.0 M. At c = 3 M both products are formed, but the ratio of their amounts in the reaction medium does not change with time.The experiments in 60 and 80% ethanol at HCl concentrations of 2.0 and 2.5 N (the dimethylfuran is poorly soluble in the 40% alcohol) showed that in 80% alcohol at the indicated acid concentrations only the hexanedione 2 is formed, while in 60% ethanol the concentrations of compound 2 and X oscillate in both cases (Fig. 2). __________________________________________________________________________________________

Direct photolysis of carbonyl compounds dissolved in cloud and fog droplets

“…We develop a framework that allows for the prediction of the aqueous photolysis lifetime as a function of wavelength and maximal optical extinction associated with the 5 yields for atmospherically relevant carbonyls, we chose dihydroxyacetone and glyceraldehyde as surrogates for oxidized water soluble atmospheric organic compounds. Dihydroxyacetone and glyceraldehyde contain both carbonyl and hydroxyl functional groups (see Figure 1), have large predicted effective Henry's law constants (5.5 x 10 8 M atm -1 (EPA, 2013) and 2 x 10 8 M atm -1 (Saxena and Hildemann, 1996), respectively), and do not hydrate completely in the aqueous-phase (fraction unhydrated ≈ 77% (Glushonok et al, 2003) and 5% (Glushonok et al, 1986) at 25 o C, respectively). In addition, glyceraldehyde has been identified as a product of isoprene oxidation (Fang et al, 2012) and may be present in automobile exhaust (Renzetti and Doyle, 1959).…”

“…Dihydroxyacetone and glyceraldehyde contain both carbonyl and hydroxyl functional groups (see Fig. 1), have large predicted effective Henry's law constants (5.5 × 10 8 M atm −1 (EPA, 2013) and 2 × 10 8 M atm −1 (Saxena and Hildemann, 1996), respectively), and do not hydrate completely in the aqueous phase (fraction unhydrated ≈ 77 % (Glushonok et al, 2003) and 5 % (Glushonok et al, 1986) at 25 • C, respectively). In addition, glyceraldehyde has been identified as a product of isoprene oxidation (Fang et al, 2012) and may be present in automobile exhaust (Renzetti and Doyle, 1959).…”

“…All predicted rate constants were capped at the diffusion controlled limit of 10 10 M −1 s −1 . Complete extinction coefficients across all actinic wavelengths were not available for most compounds, but published values of λ max and ε max are available for many carbonyl compounds (Xu et al, 1993;Malik and Joens, 2000;Steenken et al, 1975;Hammond et al, 1959;Mackinney and Temmer, 1948;Schutze and Herrmann, 2004;Rice, 1920;Gubina et al, 2004). For simple mono-and di-carbonyl compounds without published λ max and ε max values (76 out of 92 total compounds), we made educated upper estimates based on the values of compounds with similar functionality.…”