Theoretical Study on Reaction Pathways Leading to CO and CO₂ in the Pyrolysis of Resorcinol

Abstract

Possible pathways for the pyrolysis of resorcinol with the formation of CO and CO as final products were proposed and evaluated using ab initio calculations. Our experimental study revealed that large quantities of CO are generated in the pyrolysis of 1,3-dihydroxybenzene (resorcinol), while the pyrolysis of the dihydroxybenzene isomers 1,2-dihydroxybenzene (catechol) and 1,4-dihydroxybenzene (hydroquinone) produces little CO. The fate of oxygen atoms in catechol and hydroquinone was essentially the formation of CO. In the proposed pathways, the triplet ground state m-benzoquinone was generated initially from simultaneous cleavage of the two O-H bonds in resorcinol. Subsequently, the direct cleavage of a C-C bond of the m-benzoquinone diradical yields 2-oxidanylcyclopenta-2,4-dien-1-yl-methanone, which can be converted via two channels: release of CO from the aldehyde radical group and combination of the ketone radical and carbon atom in the aldehyde radical group to form the 6-oxabicyclo[3.2.0]hepta-2,4-dien-7-one, resulting in the release of CO. Potential energy surfaces along the proposed reaction pathways were calculated employing the CBS-QB3 method, and the rate constants at the high-pressure limit were also evaluated based on transition-state theory to assess the feasibility of the proposed reaction pathways.

New analytical tools for advanced mechanistic studies in catalysis: photoionization and photoelectron photoion coincidence spectroscopy

“…The counter product was hypothesized to be cyclopentadiene 97 or a C5H4 species. 99 Only recently could Gerlach et al show conclusively using PEPICO detection 98 that resorcinol decarboxylation proceeds over acyclic C5H6 species, such as 1,2,4-pentatriene, Eand Z-1-butyne-3-ene, and 1-butyne-4-ene at moderate reactor temperatures (Figure 8a). Franck-Condon spectral modelling and high-level adiabatic ionization energy calculations yielded a definitive assignment of the C5H6 isomers.…”

Isomer-dependent catalytic pyrolysis mechanism of the lignin model compounds catechol, resorcinol and hydroquinone

“… 17 Based on computations, a biradical reaction pathway was proposed. 18 By using in situ photoelectron photoion coincidence (PEPICO) methods, we found compelling spectroscopic evidence ( vide infra ) that the resorcinol decomposition mechanism is dominated by a retro-Diels–Alder reaction to produce CO 2 and C 5 H 6 isomers (R1) instead or it leads to two highly reactive ketenes species (R1). 18,19 Furthermore, the three benzenediols share the same reaction to form cyclopenta-2,4-dien-1-ol (C 5 H 6 O) and 2,4-cyclopentadiene-1-one (C 5 H 4 O), initiated by CO loss in a phenolic keto–enol tautomerism pathway (see R2 for an overview).…”

Metamorphic meta isomer: carbon dioxide and ketenes are formed via retro-Diels–Alder reactions in the decomposition of meta-benzenediol

“…However, their kinetics calculations suggested that decarboxylation is not feasible, at odds with their experimental data. 20 Among the three benzenediols, Ormond et al found that only the meta isomer resorcinol yields C5H6 species and CO2, and decarboxylation is completely absent for catechol (CAT) and hydroquinone (HYD). 18 Similar isomer-selective reactivity was also observed for xylyl radicals.…”