Introduction The identification and exact nature of radicals from lignin pyrolysis in the gas phase is highly challenging. In this regard, the investigation of pyrolysis / degradation mechanisms of the lignin monomer / structural units', such as p-coumaryl, coniferyl and sinapyl alcohols, will mimic the complex process of lignin pyrolysis and most importantly, will simplify the identification process of intermediate radicals. For this purposes a series of experimental work and theoretical calculations were initiated to identify the nature and origin of intermediate, gas phase radicals from thermal degradation one of the monolignols, p- coumaryl alcohol (pCoumA).ExperimentalMaterials:  p- coumaryl alcohol - 2-propen - 1-ol, 3 (p - hydroxyphenyl) was provided by Ryan Scientific Inc. and used without further purification.EPR measurements:  The pyrolysis reactor in conjunction with Cold Finger EPR spectroscopy is represented elsewhere1.Computational Calculations: Theoretical calculations were performed using QChem 4.101 quantum chemistry package.Results and Discussion A structure less, anisotropic EPR spectrum was detected at 77 K from pCoumA gas-phase pyrolysis at 450 oC. The EPR preliminary results show an inhomogeneous broadening character of spectra as a mixture of radicals. The primary bond dissociation energies in p-coumaryl alcohol calculated at M06-2X/6-31G(d,p) DFT level are shown in  . It is obvious that the lowest energy processes involve loss of those hydrogen atoms that lead to the formation of highly conjugated radicals, as well as the elimination of terminal hydroxyl and hydroxymethyl radical fragments.Conclusion: Based on preliminary experimental and computational results it can be established the complex nature of radicals detected from pCoumA gas-phase pyrolysis.Acknowledgement. We acknowledge the financial support of this work through NSF grant number 1330311.References 1. Khachatryan, L.; Adounkpe, J.; Maskos, M., and ; Dellinger, B., Formation of Cyclopentadienyl Radicals from the Gas-Phase Pyrolysis of Hydroquinone, Catechol, and Phenol. Environ. Sci. Technol. 2006,  40, 5071-5076.

Intermediate radicals from thermal degradation of p-coumaryl alcohol in the gas phase

248th National Meeting (2014)

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