60th Annual Report on Research 2015

Technical Progress: Pyrolysis of Branched-Chain Aldehydes

The pyrolysis of branched-alkyl chain aldehydes has been studied in a pulsed hyperthermal nozzle.  The goal of these experiments is to identify, via matrix-isolation FTIR, the products of gas-phase pyrolysis of pivaldehyde and isovaleraldehyde. (Figure 1)  This information will ultimately lead to a better understanding of the pyrolysis mechanism.  The results will be compared to the pyrolysis products of small, unbranched aldehydes that are described in the literature: acetaldehyde, propionaldehyde, and butyraldehyde. 

Figure 1.  Pivaldehyde (left) and isovaleraldehyde (right)

In the second year of PRF support, efforts have been focused on analyzing FTIR spectra collected following pyrolysis of isovaleraldehyde and pivaldehyde (in separate experiments) in the temperature range of 600-1200 ºC.  Products identified include: carbon monoxide, vinyl alcohol, and various alkenes.  It is suspected that there are additional products related to unsaturated hydrocarbons or ketenes. Identification of these species is difficult because there are no FTIR spectra in the literature for the matrix-isolated products.  To overcome this challenge, we have begun a computational chemistry study of a series of ketenes and alkynes.  Structures for the various molecules have been optimized in Gaussian 09 and the predicted frequencies have been scaled for comparison to experimental data.

Another aspect of this project seeks clues to the mechanism governing the decomposition of isovaleraldehyde and pivaldehyde.  Our previous work established that each of these compounds decomposes to isobutene.  There is a plausible, proposed mechanism for the production of isobutene but it is unknown whether isobutene decomposes further under the experimental conditions used here.  To understand isobutene’s role in the overall pyrolysis mechanism, we have begun pyrolysis experiments in the 600-1200 °C range.  Preliminary results indicate that isobutene does not react.  (Figure 2)

Figure 2.  Matrix-isolation FTIR spectra collected following pyrolysis of a 1:250 isobutene:argon mixture at 1000 °C (top), (B) of an unheated 1:250 isobutene:argon mixture, and (C) of argon after heating to 1000 °C

Technical Progress: Isolation of the Acetonyl Radical

          The goal of this project is to produce the acetonyl in the gas phase and isolate it in an argon matrix for characterization via FTIR.  We have synthesized 4-nitrosooxy-2-butanone was investigated as a possible pyrolytic precursor molecule.  (Figure 3)  Previous work in this lab showed that the precursor decomposes to make formaldehyde as predicted, but the acetonyl radical was unstable, forming ketene through loss of a hydrogen atom.  In this second year of PRF support, we have attempted pyrolysis at lower temperatures and have seen FTIR evidence that the acetonyl may survive.  Frequency calculations were performed with Gaussian 09 on this radical to aid in assignment of the FTIR spectrum and verify that the radical has been isolated. 

Figure 3.  Synthesis of 4-nitrosooxy-2-butanone and the suspected reaction for subsequent pyrolysis     Technical Progress: Identifying Pyrolysis Reactions of 3-Oxetanone           The pyrolysis of 3-oxetanone was investigated to determine if more than one thermal decomposition pathway is accessible in the 400-1200 °C temperature range.  This project was a continuation of work originally supported by the Camille and Henry Dreyfus Foundation.  Dissociation studies in the literature reported the production of formaldehyde and ketene from 3-oxetanone.  Our work shows that ethylene oxide and carbon monoxide are also produced during pyrolysis, and the ethylene oxide can undergo subsequent reactions. (Figure 4) This work was published in the Journal of Physical Chemistry A in June 2015.¹                              Figure 4.  Summary of the pyrolysis reactions of 3-oxetanone.

Impact on Undergraduate Students

Three students were directly supported by PRF funds in the summer of 2015.  Eric Sias and Sarah Cole are juniors majoring in chemistry. John Sowards is a sophomore chemistry major. All three students collaborated in the collection of matrix-isolation FTIR spectra for the projects described here, but each one was designated the lead student for their own project.  These students are continuing their research in the 2015-2016 academic year. 

The benefit to the involved students far exceeds their summer employment.  The students participated in the Department of Chemistry’s summer research program, which included approximately 20 undergraduate students, M.S. students, and local high school students and teachers working in Marshall chemistry faculty labs.  Participants gave short proposal talks at a kickoff luncheon, toured a local refinery, and engaged in social activities with professors.  The summer experience culminated in a formal research symposium featuring 10-15 minute oral presentations.  Eric Sias has presented a poster of his results from the 4-nitrosooxy-2-butanone project at the October 2014 ACS Central Regional Meeting in Pittsburgh and the Fall 2015 ACS National Meeting.  It is anticipated that every student supported by PRF will have an opportunity to present research at a conference, which will greatly enhance their professional development.

Impact on Career of the PI

Research support from PRF has enabled the PI to retain undergraduate researchers for multiple years of research.  This allows students to gain independence in their daily experiments and gives them time to see projects through to the end.  The one current publication, plus anticipated future publications resulting from PRF support places the PI in a good position to attract new external funding in the future.

1.  Wright, E. M.; Warner, B. J.; Foreman, H. E.; McCunn, L. R.; Urness, K. N. Pyrolysis Reactions of 3-Oxetanone. J. Phys. Chem. A 2015, 119, 7966-7972.