Thermochemistry and Kinetics of Angelica and Cognate Lactones

Würmel, Judith; Simmie, John M.

doi:10.1021/jp502310v

Cited by 11 publications

(23 citation statements)

References 47 publications

(66 reference statements)

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“…The enthalpies of formation of the species encountered in this work were determined by using the appropriate furanone parent compound that we had previously computed 12 and adding the reaction enthalpy (together with the formation enthalpy of well-known species such as CO as and if required); these are then catalogued in Table 1 In some cases two or more channels lead to the same species, and in those cases the listed values are the average of those possibilities. Exact agreement with our previous work is unlikely since multiple composite methods were used before, whereas in this work we are relying on a single model chemistry, namely, CBS-QB3.…”

Section: ■ Resultsmentioning

confidence: 99%

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

et al. 2015

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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.

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Section: ■ Resultsmentioning

confidence: 99%

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

et al. 2015

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“…the local flow velocity reaches the local speed of sound) to produce an underexpanded supersonic jet downstream, an important characteristic for molecular studies (see for example Anderson et al 42 ). The important results obtained from these simulations are the temperature and pressure profiles of the internal gas as a function of external wall temperature, with the centerline 36 8.97 ± 0.05 41 † average of CBS-QB3, G3 and CBS-APNO methods * dihedrals O=C-C-C and CCCC ‡ see Schemes 4 and 5 for structural information profiles shown in Figure 1. The application Chemkin 43 was also used to simulate the reacting flow; details of these simulations are presented in the Kinetics section.…”

Section: Reactor Modelingmentioning

confidence: 99%

“…Products Table 1, 5-methyl-2(5H)-furanone, formed by addition of CH 3 at C5 on methoxyfuran, has an ionization threshold just above 10 eV. 36 If the intermediate was the result of CH 3 addition at C3, as in Scheme 4.2, the predicted ionization threshold for this methylated 2(3H)-furanone is 1 eV lower in energy.…”

Section: Addition Reactions Of H and Chmentioning

confidence: 99%

“…Scheme 5: Possible products resulting from reaction of H and CH 3 with 2-furanyloxy radical, including calculated reaction barriers. 36 Refer to Scheme 4.5 and Scheme 3.4 for structure of ringopened intermediates (see Refs. 36, 57, 58 and 56 for more detailed theoretical predictions and experimental observations of several lactones).…”

Section: Reactions With 2-furanyloxy Radicalmentioning

confidence: 99%

“…mass 83. 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 9.5−10 eV, which could indicate the possibility of both 2(3H)-furanone (IE = 9.3−9.7 eV) and 2(5H)-furanone (IE = 10.2−10.65 eV) 36,37. The ionization energy 37 of 2(5H)-furanone is likely lower than the reported value of 10.65 eV; samples of 2(5H)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.…”

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Pyrolysis Pathways of the Furanic Ether 2-Methoxyfuran

et al. 2015

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Substituted furans, including furanic ethers, derived from nonedible biomass have been proposed as second-generation biofuels. In order to use these molecules as fuels, it is important to understand how they break apart thermally. In this work, a series of experiments were conducted to study the unimolecular and low-pressure bimolecular decomposition mechanisms of the smallest furanic ether, 2-methoxyfuran. Electronic structure (CBS-QB3) calculations indicate this substituted furan has an unusually weak O-CH3 bond, approximately 190 kJ mol(-1) (45 kcal mol(-1)); thus, the primary decomposition pathway is through bond scission resulting in CH3 and 2-furanyloxy (O-C4H3O) radicals. Final products from the ring opening of the furanyloxy radical include 2 CO, HC≡CH, and H. The decomposition of methoxyfuran is studied over a range of concentrations (0.0025-0.1%) in helium or argon in a heated silicon carbide (SiC) microtubular flow reactor (0.66-1 mm i.d., 2.5-3.5 cm long) with reactor wall temperatures from 300 to 1300 K. Inlet pressures to the reactor are 150-1500 Torr, and the gas mixture emerges as a skimmed molecular beam at a pressure of approximately 10 μTorr. Products formed at early pyrolysis times (100 μs) are detected by 118.2 nm (10.487 eV) photoionization mass spectrometry (PIMS), tunable synchrotron VUV PIMS, and matrix infrared absorption spectroscopy. Secondary products resulting from H or CH3 addition to the parent and reaction with 2-furanyloxy were also observed and include CH2═CH-CHO, CH3-CH═CH-CHO, CH3-CO-CH═CH2, and furanones; under the conditions in the reactor, we estimate these reactions contribute to at most 1-3% of total methoxyfuran decomposition. This work also includes observation and characterization of an allylic lactone radical, 2-furanyloxy (O-C4H3O), with the assignment of several intense vibrational bands in an Ar matrix, an estimate of the ionization threshold, and photoionization efficiency. A pressure-dependent kinetic mechanism is also developed to model the decomposition behavior of methoxyfuran and provide pathways for the minor bimolecular reaction channels that are observed experimentally.

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Ethyl lactate: a sinister molecule exhibiting high chemical diversity with potential as a “green” solvent

Würmel

Somers

Simmie

2020

Int J of Chemical Kinetics

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A comprehensive study of the properties and reactivity of ethyl(S)‐lactate has been conducted. The conformational landscape, the enthalpy of formation of the ground state, normalΔfH∘−false(00.16emnormalKfalse)=−600.2±2.2 kJ mol−1, the thermochemistry (entropy, specific heat, enthalpy function), adiabatic ionization energy, and the single bond dissociation energies are also mapped out. Unimolecular elimination reactions leading to water and ethyl acrylate or ethene and lactic acid proceed with barriers in excess of 250 kJ mol−1—with the latter always dominant. The chemical kinetics of the abstraction of H‐atoms from primary, secondary, tertiary, and alcoholic sites by the radicals H• and CH3• are calculated as well as the kinetics of addition reactions to the carbonyl bond.

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Thermochemistry and Kinetics of Angelica and Cognate Lactones

Cited by 11 publications

References 47 publications

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

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

Pyrolysis Pathways of the Furanic Ether 2-Methoxyfuran

Ethyl lactate: a sinister molecule exhibiting high chemical diversity with potential as a “green” solvent

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