Thermal Decomposition of 2(3H) and 2(5H) Furanones: Theoretical Aspects

Abstract

The thermal decomposition reactions of 2(3H) and 2(5H) furanones and their methyl derivatives are explored. Theoretical calculations of the barriers, reaction enthalpies, and the properties of these and intermediate species are reported using the composite model chemistry CBS-QB3 and also the functional M06-2X allied to the 6-311++G(d,p) basis set. Thus, the bond dissociation enthalpies, ionization energies, and unimolecular chemical kinetic rate constants in the high-pressure limit were computed. We show that flow reactor experiments that intimated that heating the 2(3H) furanone converts it to the isomeric 2(5H) furanone occurs via a 1 → 2 H-transfer reaction to an open ring ketenoic aldehyde. The latter can then ring close to the other isomeric structure. The final products acrolein and carbon monoxide are only formed from 2(3H), and acrolein will further decompose to ethylene and CO. Comparable channels explain the interconversion of 5-methyl-2(3H) furanone to its 2(5H) isomer and to the formation of methyl vinyl ketone and CO. The influence of the methyl group at other positions on the ring is hardly of significance except in the case of 5-methyl-2(5H) furanone where a hydrogen atom transfer from the methyl group leads to the formation of a doubly unsaturated carboxylic compound, 2,4-pentadienoic acid. Studies of the UV photolysis of the parent compounds in both low-temperature inert argon matrices and in solution are broadly in accord with the thermal findings insofar as product formation is concerned and with our theoretical calculations. The dominant features of the early decomposition chemistry of these compounds are simple hydrogen transfer and simultaneous ring opening reactions, which do however result in some quite unusual species.

Pyrolysis Pathways of the Furanic Ether 2-Methoxyfuran

“…Examination of PIE­( m / z 84) at 1300 K when all m / z 83 is consumed does show that trace amounts of m / z 84 grow in between 9.5 and 10 eV, which could indicate the possibility of both 2­(3 H )-furanone (IE = 9.3–9.7 eV) and 2­(5 H )-furanone (IE = 10.2–10.65 eV). , The ionization energy of 2­(5 H )-furanone is likely lower than the reported value of 10.65 eV; samples of 2­(5 H )-furanone seeded in He were pulsed through an unheated reactor, and ions at m / z 84 were detected by 10.487 eV photoionization mass spectrometry. A more detailed discussion of these experiments is reported elsewhere; a quantum chemical study of the thermochemistry and kinetics of these lactones is also presented in works by Würmel and Simmie. , …”

“…Recent electronic structure calculations indicate that the lowest-energy decomposition route of 5-methyl-2­(5 H )-furanone is ring opening to 1-pentene-1,4-dione, as shown in Scheme 4.5 . The furanone could also decompose through an addition–elimination reaction with H atom, converting the 2­(5 H ) intermediate to 5-methyl-2­(3 H )-furanone (α-angelica lactone), which has been shown to eliminate CO and produce MVK either through a concerted reaction , or through an open-chain pentene-dione intermediate . A similar addition–elimination reaction was suggested to be a favorable route to interconvert the unmethylated furanones, 2­(3 H )- and 2­(5 H )-furanone.…”

Initial Reaction Mechanism of Bio-oil High-Temperature Oxidation Simulated with Reactive Force Field Molecular Dynamics

“…It should be noted that pathway I was relatively more frequently observed than pathway II. However, pathway II is a reaction pathway experimentally observed by Xu et al 8 and calculated by Wuermel et al, 9 employing a theoretical approach. In addition, CO 2 is not the main product of 2-furanone pyrolyzing; instead, the reaction will give CO and propenal as the products.…”

“…Understanding the reaction pathways of bio-oil combustion is important for better use of bio-oil, but limited research has been reported in that regard. Oxidation or pyrolysis reaction pathways of furan- and phenol-derived compounds, such as furanone, , phenol, cresol, catechol, , hydroquinone, and dimethoxybenzene, have been largely investigated. Although the structure of these compounds is very similar to those contained in bio-oil, reactivity of furan- or phenol-derived compounds may vary during the combustion of bio-oil samples.…”

“…As a major approach for reaction pathway investigation, quantum mechanics (QM) has been used in investigating the early-stage decomposition process of anisole-, phenol-, and furan-type compounds, which are or can be considered as analogues of bio-oil components. ,,, However, the model size investigated has to be often limited to one or two molecules as a result of the very expensive computational cost of QM. In fact, the scale of the practical model for QM applications is around ∼100 atoms, which is not large enough in reaction pathway investigation to study a complex model system, such as a model of bio-oil.…”