Thermal Decompositions of the Lignin Model Compounds: Salicylaldehyde and Catechol

Thomas K. Ormond, Joshua H. Baraban, Jessica P. Porterfield, Adam M. Scheer, Patrick Hemberger, Tyler P. Troy, Musahid Ahmed, Mark R. Nimlos, David J. Robichaud, John W. Daily, G. Barney Ellison

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

The nascent steps in the pyrolysis of the lignin components salicylaldehyde ( o-HOC6H4CHO) and catechol ( o-HOC6H4OH) were studied in a set of heated microreactors. The microreactors are small (roughly 1 mm ID × 3 cm long); transit times through the reactors are about 100 μs. Temperatures in the microreactors can be as high as 1600 K, and pressures are typically a few hundred torr. The products of pyrolysis are identified by a combination of photoionization mass spectrometry, photoelectron photoion concidence mass spectroscopy, and matrix isolation infrared spectroscopy. The main pathway by which salicylaldehyde decomposes is a concerted fragmentation: o-HOC6H4CHO (+ M) → H2 + CO + C5H4═C═O (fulveneketene). At temperatures above 1300 K, fulveneketene loses CO to yield a mixture of HC≡C-C≡C-CH3, HC≡C-CH2-C≡CH, and HC≡C-CH═C═CH2. These alkynes decompose to a mixture of radicals (HC≡C-C≡C-CH2 and HC≡C-CH-C≡CH) and H atoms. H-atom chain reactions convert salicylaldehyde to phenol: o-HOC6H4CHO + H → C6H5OH + CO + H. Catechol has similar chemistry to salicylaldehyde. Electrocyclic fragmentation produces water and fulveneketene: o-HOC6H4OH (+ M) → H2O + C5H4═C═O. These findings have implications for the pyrolysis of lignin itself.

Original languageEnglish GB
Pages (from-to)5911-5924
Number of pages14
JournalJournal of Physical Chemistry A
Volume122
Issue number28
DOIs
StatePublished - 19 Jul 2018

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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