Kinetics of the Reactions of Hydroxyl Radicals with Furan and Its Alkylated Derivatives 2-Methyl Furan and 2,5-Dimethyl Furan

Temperature-Dependent, Site-Specific Rate Coefficients for the Reaction of OH (OD) with Methyl Formate Isotopologues via Experimental and Theoretical Studies

Methyl esters are an important component of combustion and atmospheric systems. Reaction with the OH radical plays an important role in the removal of the simplest methyl ester, methyl formate (MF, CH3OCHO). In this paper, the overall rate coefficients for the reactions of OH and OD with MF isotopologues, studied under pseudo-first-order conditions, are reported using two different laser flash photolysis systems with the decay of OH monitored by laser-induced fluorescence. The room-temperature rate coefficient for OH + MF, (1.95 ± 0.34) × 10-13 cm3 molecule-1 s-1, is in good agreement with the literature. The rate coefficient exhibits curved Arrhenius behavior, and our results bridge the gap between previous low-temperature and shock tube studies. In combination with the literature, the rate coefficient for the reaction of OH with MF between 230 and 1400 K can be parametrized as kOH+MF = (3.2 × 10-13) × (T/300 K)2.3 × exp(-141.4 K/T) cm3 molecule-1 s-1 with an overall estimated uncertainty of ∼30%. The reactions of OD with MF isotopologues show a small enhancement (inverse secondary isotope effect) compared to the respective OH reactions. The reaction of OH/OD with MF shows a normal primary isotope effect, a decrease in the rate coefficient when MF is partially or fully deuterated. Experimental studies have been supported by ab initio calculations at the CCSD(T)-F12/aug-cc-pVTZ//M06-2X/6-31+G** level of theory. The calculated, zero-point-corrected, barrier heights for abstraction at the methyl and formate sites are 1.3 and 6.0 kJ mol-1, respectively, and the ab initio predictions of kinetic isotope effects are in agreement with experiment. Fitting the experimental isotopologue data refines these barriers to 0.9 ± 0.6 and 4.1 ± 0.9 kJ mol-1. The branching ratio is approximately 50:50 at 300 K. Between 300 and 500 K, abstraction via the higher-energy, higher-entropy formate transition state becomes more favored (60:40). However, experiment and calculations suggest that as the temperature increases further, with higher energy, less constrained conformers of the methyl transition state become more significant. The implications of the experimental and theoretical results for the mechanisms of MF atmospheric oxidation and low-temperature combustion are discussed.

Theoretical Studies on the Reaction Kinetic of 2-Acetylfuran with Hydroxyl Radicals

With the development of synthetic methods, 2-acetylfuran (AF2) has become a potential biomass fuel. The potential energy surfaces of AF2 and OH including OH-addition reactions and H-abstraction reactions were constructed by theoretical calculations at the CCSDT/CBS/M06-2x/cc-pVTZ level. The temperature- and pressure-dependent rate constants of the relevant reaction pathways were solved based on transition state theory and Rice-Ramsperger-Kassel-Marcus theory, as well as Eckart tunneling effect correction. The results showed that the H-abstraction reaction on CH₃ on the branched chain and the OH-addition reaction at the C (2) and C (5) sites on the furan ring were the main reaction channels in the reaction system. At low temperatures, the AF2 and OH-addition reactions dominate, and the percentage decreases gradually to zero with increasing temperature, and at high temperatures, the H-abstraction reactions on the branched chains become the most dominant reaction channel. The rate coefficients calculated in the current work improve the combustion mechanism of AF2 and provide theoretical guidance for the practical application of AF2.

Analysis of Furan in Red Pepper Powder Treated by Three Methods-Boiling, Roasting, and Frying

In this study, furan analysis was conducted on dried red pepper powder treated by three cooking methods (boiling, roasting, and frying). A total of 144 samples were prepared and their furan levels were analysed using automated solid-phase micro-extraction gas chromatography-mass spectrometry. The furan concentration in boiled soup ranged from 1.26 to 4.65 ng/g, and from 7.37 to 27.68 ng/g for boiled red pepper samples. For the roasting method, a furan concentration between 6.66 and 761.37 ng/g was detected. For the frying method, the furan level of edible oils ranged from 3.93 to 125.88 ng/g, and a concentration ranging from 4.88 to 234.52 ng/g was detected for the fried red pepper samples. The cooking method using edible oil obtained a higher furan concentration than the water-based method. Samples using corn germ oil (linoleic acid-rich oil) obtained the highest furan concentration among the four edible oils. In all cooking methods, the higher the heating temperature and time, the higher the furan concentration detected. A kinetic study was conducted using the roasting model system and the apparent activation energy was 60.5 kJ/mol. The results of this study could be useful as a database for furan concentration in dried red pepper powder according to various cooking methods.