May 16, 2005 ITHACA, N.Y. -- Scientists have discovered compounds nearly ubiquitous in fire that have amazingly eluded detection in spite of 150 years of research on how flames burn.
According to a paper in the journal Science on its Science Express Web site (May 12), co-authored by a Cornell University professor, enols, technically in the family of alcohols, are part of the chemical pathway that occurs when a wide variety of fires burn.
Scientists who study combustion never expected to find enols in flames, and until now their detection was obscured by another related compound that shares the same mass and has long been known to exist in fire. A new technique for studying the compounds in flames has allowed researchers to distinguish between these molecules and has made the discovery possible.
"We've found there is this whole class of previously unsuspected chemistry going on in flames," says Terrill Cool, professor of applied and engineering physics at Cornell.
"It is remarkable that even after 150 years of flame chemistry research new compounds can be found," says Craig Taatjes, a combustion chemistry researcher at Sandia National Laboratory in Livermore, Calif., and lead author of the paper.
While the researchers don't know where the discovery will lead, it offers new directions in efforts to reduce soot and other pollutants in flames, improve fuel cells, and model planetary atmospheres and interstellar chemistry.
Enols have a structure that includes properties of both alkenes and alcohols, hence the name (enol). The simplest alkene is ethylene (C2H4), a gas that is produced in nature as a plant hormone and is also a major chemical feedstock (the starting point for manufacturing other substances). The primary commercial use of ethylene is the production of polyethylene, a common plastic. When a hydroxyl group (OH) replaces a hydrogen atom in ethylene, it becomes an enol called ethenol (CH2CHOH), also known as vinyl alcohol. Ethenol exists only as a transient or fleeting species in chemical reactions, but altered, stable forms of ethenol (polyvinyl alcohol) are main ingredients in latex paints, hair sprays, shampoos and glues.
Hundreds of chemical species form and turn into other products when fires burn. Enols are one of these intermediary species. To study fire chemistry, researchers use computer models to simulate chemical reactions during combustion. Now, models must be modified to include enols. Also, by understanding the chemistry of burning from beginning to end, researchers may be able to alter pathways and reduce pollutants, such as soot, that come out of flames.
Astronomers have observed ethenol in interstellar space. The new enol findings could provide clues as to how complex organic molecules form in interstellar space.
A common technique used to determine the components in fire involves taking a sample of the chemicals in a flame, giving them an electrical charge and timing how long it takes for the electrically charged molecules, called ions, to reach a detector. Heavier ions take longer, so researchers calculate a molecular mass based on timing. Scientists use the results to make models of chemical reactions that occur during combustion.
Until now, scientists who study combustion never suspected enols existed in flames. They knew of another closely related molecule (called an isomer) that shares the same composition and mass, is also an intermediary, but has a different structure, which alters its physical and chemical properties
The researchers applied a new technique that reveals both the structure and the mass. The technique relies on the fact that forming ions from different isomers requires different amounts of energy. By making the ions with photons, or particles of light, tuned to specific energies, isomers can be distinguished.
"The new technique allows us to look at things people couldn't see before," said Cool. "We weren't looking for ethenol. Nobody had suspected it was there, but then we found it."
Other than Taatjes, Cool's co-authors include other researchers from the Sandia National Laboratory, the University of Massachusetts-Amherst, the University of Science and Technology of China and the University of Bielefeld (Germany).
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