Pyrolysis and MatrixIsolation FTIR of Acetoin Sarah L

Pyrolysis and Matrix-Isolation FTIR of Acetoin Sarah L. Cole, David Thacker, Martha J. Ellis, John R. Sowards, Laura R. Mc. Cunn Marshall University, Huntington, West Virginia

Acetoin § naturally occurring in plants, animals, and fermented products § flavor enhancer in foods and cigarettes www. ecigclick. co. uk § alternative to diacetyl flavoring § detected in biomass pyrolysates

Motivation • There are no published experiments on thermal decomposition of acetoin. • Acetoin appears in many products and processes where high temperatures are involved. Experimental Approach • Conduct gas-phase pyrolysis experiments at various temperatures and identify products using matrix-isolation FTIR

Pyrolysis and Matrix-Isolation FTIR 0. 2 Torr acetoin entrained in 700 Torr argon behind a 40 -Hz pulsed valve Supersonic jet of products/Ar expanding into cryostat at 10 -6 Torr 1 mm x 3. 8 cm Si. C tube @ 300– 1500 K 5 K Cs. I window for FTIR spectroscopy Zhang, et al. , Rev. Sci. Instrum. , Vol. 74, No. 6, June 2003

Pyrolysis Temperature Study

Carbon Monoxide 2138 CO 2149 H 2 O·CO The CO absorption following acetoin pyrolysis was integrated and compared to the integrated signal in the argon spectrum to prove that carbon monoxide is a product of pyrolysis.

Carbon Dioxide 2138 CO 2149 H 2 O·CO CO 2 Carbon dioxide was also shown to be a product of acetoin pyrolysis by comparison of the integrated signals.

Ketene? 2142 Ketene or Propyne The peak at 2142 cm-1 was integrated to verify that the signal was due to pyrolysis of acetoin at 1300 K.

Ketene verified Ketene H 2 C=C=O Band at 1380 cm-1 was also observed.

Ketene and Propyne? 2142 Ketene or Propyne

Verification of Propyne CH 3 C≡CH Bands at 629, 1446, and 2963 cm-1 also observed. Acetylene HC≡CH Band at 736 cm-1 also observed. Ketene H 2 C=C=O

Vinyl Alcohol and Propene CH 3 CH=CH 2 Band at 2923 cm-1 also observed. Vinyl Alcohol Bands at 1622 cm-1 and 3620 cm-1 also observed. Ketene H 2 C=C=O

Aldehydes 1300 K pyrolysis Acetaldehyde CH 3 C(O)H Bands at 1349 cm-1 and 2736 cm-1 also observed. Unheated acetoin Formaldehyde H 2 CO Bands at 2863, 2798, 1244 and 1170 cm-1 also observed. Propyne CH 3 C≡CH

Hydrocarbons Propyne CH 3 C≡CH Ethylene CH 2=CH 2 Other bands at 948 cm-1, 3080 cm-1 and 3111 cm-1 Propane CH 3 CH 2 CH 3 Other bands at 743, 868, 918, 1050, and 1156 cm-1 Acetaldehyde CH 3 C(O)H Ketene H 2 C=C=O

Pyrolysis Products Observed CO H 2 C=C=O CH 3 CHO CH 2=CHOH CH 2=CH 2 HC≡CH CH 3 CH 2 CH 3 CH=CH 2 CH 3 C≡CH CO 2 carbon monoxide ketene acetaldehyde vinyl alcohol ethylene acetylene propane propene propyne carbon dioxide consistent with proposed reactions or analogous to pyrolysis of similar compounds suggest bimolecular reactions

Previously Suggested Reactions Acetoin is one product of the pyrolysis of calcium alginate fiber at 400 °C. Two reactions of acetoin were proposed as consistent with the observed products of calcium alginate pyrolysis: ? + One confirmed peak at 1779 cm-1 ? + H 2 One confirmed peak at 947 cm-1 Zhang et al. Polymer Degradation and Stability 96 (2011) 936 -942.

C-C Fission Reactions + CH 3 + CO or H + ketene CH 3 + CO vinyl alcohol acetaldehyde formaldehyde ketene CH 3 acetaldehyde or vinyl alcohol

Possible Hydrogen Abstractions H 2 C=C=O + OR OR H 2 C=C=O + +

Pyrolysis Products CO H 2 C=C=O CH 3 CHO CH 2=CHOH CH 2=CH 2 HC≡CH CH 3 CH 2 CH 3 CH=CH 2 CH 3 C≡CH CO 2 CH 3 COOH CH 3 C(O)CH 3 carbon monoxide ketene acetaldehyde vinyl alcohol ethylene acetylene propane propene propyne carbon dioxide acetic acid diacetyl methyl radical consistent with proposed reactions or analogous to pyrolysis of similar compounds suggest bimolecular reactions *difficult to detect

Future Work • complete assignments of vibrational spectra • perform mass spectrometry (in collaboration) to identify missing/questionable products • consider thermochemistry and kinetics of proposed reactions

Acknowledgments Sarah Cole ’ 17 (MU Med. School) Martha Ellis ‘ 19 David Thacker ‘ 17 Glenna Brown ‘ 19 Omar Bhatti ’ 20 John Sowards ’ 18 Eric Sias ‘ 16 (MU Med. School) ACS Petroleum Research Fund Camille and Henry Dreyfus Foundation Research Corporation for Science Advancement NASA-WV Space Grant Consortium Marshall University SURE Program MU Chemistry Summer Research Fellowship