Courtney Hatten, Brian Warner, Emily Wright, Kevin Kaskey, Laura R. McCunn Marshall University June 18, 2013

Relevance of aldehyde decomposition  Largest of the aldehydes typically detected in biomass pyrolysates  Also found in exhaust of biodiesel engines  Trace component of roasted coffee beans, cigarette smoke butyraldehyde Ellison Lab studied the pyrolysis of acetaldehyde Barney Ellison (CU Boulder) Vasiliou et al. J. Chem. Phys. 2011, 135,

 Ongoing effort to study thermal decomposition of a series of aldehydes butyraldehydeisovaleraldehydepivaldehydepropionaldehyde Relevance of aldehyde decomposition  Largest of the aldehydes typically detected in biomass pyrolysates  Also found in exhaust of biodiesel engines  Trace component of roasted coffee beans, cigarette smoke butyraldehyde

Anticipated Thermal Decomposition Pathways CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH 2 + CO + H radical decomposition CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH=C=O + H 2 elimination CH 3 CH 2 CH 2 CHO → CH 3 CH 2 C ≡ CH + H 2 O isomerization/elimination Experimental Approach Conduct pyrolysis experiments at various temperatures and identify products Evaluate the effect of size and structure of alkyl chain on pyrolysis mechanism Pyrolysis reactions of butyraldehyde CH 3 CH 2 CH=C(H)OH → CH 3 CH 2 C ≡ CH + H 2 O

Supersonic jet of products/Ar expanding into cryostat at Torr 5 K CsI window for FTIR spectroscopy 2.3 Torr butyraldehyde entrained in 700 Torr argon behind a 20-Hz pulsed valve 1 mm x 3.8 cm SiC 300–1700 K Zhang, et al., Rev. Sci. Instrum., Vol. 74, No. 6, June 2003 Pyrolysis and Matrix-Isolation FTIR

Zhang, et al., Rev. Sci. Instrum., Vol. 74, No. 6, June 2003 Photoionization Mass Spectrometry (PIMS) reflectron TOF mass spectrometer nm (10.5 eV) VUV photoionization 2.3 Torr sample molecule entrained in 700 Torr argon behind a pulsed valve operating at 20 Hz 1 mm x 3.8 cm SiC 300–1700 K PIMS experiments at Ellison Lab at U. Colorado, Boulder

CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 CH 2 + CO + H H 2 O·CO CO Expected band for CH 3 CH 2 CH ) Radical Decomposition Reaction

Expected band for CH 3 CH 2 CH ) Evidence of Propyl Radical Propyl radical is either difficult to see in IR spectrum, or is undergoing secondary decomposition. m/z = 43 CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 CH 2 + CO + H

CH 3 CH 2 CH 2 CHO + ∆ CH 3 CH 2 CH 2 · CH 3 · + CH 3 CH=CH 2 + H HC ≡CH +H2H2 + CO + H Secondary Reaction Pathways CH 2 =CH 2

PIMS Evidence CH 3 propene / ketene

PropeneEthylene Ketene Secondary Products from Propyl Ethylene and propene confirmed by MI-FTIR and PIMS Methyl radical could not be found by MI-FTIR

Ethylketene Ethylketene via elimination 1141 CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH=C=O + H 2

Ethylketene via elimination m/z = 70 CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH=C=O + H 2

Ethylketene via elimination m/z = 70 CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH=C=O + H 2

CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 C≡CH + H 2 O H2OH2O Isomerization / Elimination Reaction Observed intensities of H 2 O are higher than what would be expected from ambient water vapor.

) This peak could possibly be butyne, but we need a literature comparison to be certain. Isomerization / Elimination Reaction CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 C≡CH + H 2 O

Butyne in the mass spectra? m/z = 54 Butyne (IE = 10.2 eV) is not immediately apparent. CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 C≡CH + H 2 O

Butyne in the mass spectra? m/z = 54 Butyne (IE = 10.2 eV) is not immediately apparent. CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 C≡CH + H 2 O

CH 3 CH 2 CH 2 CHO + ∆ CH 3 CH 2 C≡CH CH 3 · +∙CH 2 C≡CH + H 2 O Secondary Reaction Pathways Propargyl radical resonance-stabilized precursor to PAHs and soot methane acetylene ethylene ethane allene propyne C 4 H 2 vinylacetylene 1,2- and 1,3- butadienes benzene 80-reaction mechanism in shock-tube study King, K. Int. J. Chem. Kin. 1978, 10, 545. Hidaka, Y. Int. J. Chem. Kin. 1995, 27, 321.

Assignment of the Enol There is no literature for comparison of the FTIR spectrum of 1-buten-1-ol, however, the enol tautomer of acetaldehyde has OH features at 1663 cm -1 and 3619 cm CH 3 CH 2 CH 2 CHO + ∆ → CH 3 CH 2 CH=C(H)OH → CH 3 CH 2 C≡CH + H 2 O

m/z = 44 Vinyl alcohol CH 2 =C(H)OH vinyl alcohol IE = 9.3 eV

H-shift and Elimination CH 3 CH 2 CH 2 CHO → CH 2 =CH 2 + CH 2 =CHOH Shorter-chain aldehydes cannot access this reaction pathway. The direct production of vinyl alcohol provides a route to acetaldehyde.

Unimolecular Reaction Pathways Thermal Decomposition Pathways CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH 2 + CO + H radical decomposition CH 3 CH 2 CH 2 CHO → CH 3 CH 2 CH=C=O + H 2 elimination CH 3 CH 2 CH 2 CHO → CH 3 CH 2 C ≡ CH + H 2 O isomerization/elimination CH 3 CH 2 CH 2 CHO → CH 2 =CH 2 + CH 2 =CHOH H-shift/elimination Strong evidence in FTIR Present in both FTIR and mass spectra Mass spectra only (weak)

Summary of Pyrolysis Products ProductPIMS Matrix-isolation FTIR Comments CH 3 H2OH2O HCCH CH 2 CO HCO CH 2 CCH CH 3 CCH CH 3 CHCH 2 H 2 CCO CH 3 CH 2 CH 2 CH 2 CHOH CH 3 CH 2 CH 3 C4H2C4H2 C4H4C4H4 CH 3 CH 2 C≡CH ?no literature comparison for MI-FTIR 1- or 2- butene ? CH 3 CH 2 CHCO CH 3 CH 2 CHCHOH??no literature comparison for MI-FTIR 1° 1° = primary reaction product PAH PAH = precursor to polycyclic aromatic hydrocarbons * = products of acetaldehyde pyrolysis * * * * * * *

Camille and Henry Dreyfus Foundation Research Corporation for Science Advancement MU-ADVANCE NASA-WV Space Grant Consortium Marshall University SURE Acknowledgments

Marshall Undergraduates Courtney Hatten ‘13 (Marshall Med. School) Emily Wright ‘15 Brian Warner ’15 Sara Lilly ’12 (Marshall Med. School) Allison Combs ’12 (VT Med. School) Kevin Kaskey ’12 (Advanced Testing Labs) Acknowledgments U. Colorado, Boulder Lab Barney Ellison Jong Hyun Kim Jesse Porterfield

Mass spectra summarized CH 3 propargyl propyne ketene propene vinyl alcohol, propane 1-butene C4H2C4H2 ethylketene C4H4C4H4 HCO? 1-butyne