Since the study of modern chemistry was initiated, only 36 basic types of chemical reactions have been fully described. Recently, researchers at MIT, building on the work of another study published 30 years ago, have fully described the mechanisms of a 37th reaction –  a low-temperature oxidation that results in the decomposition of complex organic molecules known as gamma-ketohydroperoxides. The reaction is an important part of atmospheric reactions that lead to the formation of climate-affecting aerosols; biochemical reactions that may be important for human physiology; and combustion reactions in engines.

Stephen Klippenstein, a senior scientist at the Argonne National Laboratory in Illinois who was not involved in this research, says, “I think this may be the best paper I have read this year. It uses a multitude of theoretical methods … to explore multiple aspects of a novel discovery that has important ramifications in atmospheric chemistry, combustion kinetics and biology.”

Diagram illustrates the newly-discovered reaction that transforms molecules of ketohydroperoxide into acids and carbonyl molecules, after going through intermediate stages.
ILLUSTRATION COURTESY OF JALAN ET AL

Stefan Korcek, and engineer for Ford Motor Company, first described the reaction some 30 years ago, prompted by the need to better understand  how engine oils break down through oxidation – a major factor that contributes to oil waste. Since waste oil is among the largest hazardous waste streams in the United States, understanding the chemical mechanisms that lead to its degradation is very important. In his paper, Korcek outlined an unusually complex multipart reaction, whose products included carboxylic acids and ketones, and made some predictions on how the reaction takes place step-by-step. Nobody took the interest, however, to verify these findings. Not until MIT graduate student Amrit Jalan, chemical engineering professor William Green, and six other researchers decided to take a thorough look.

Jalan says that the MIT researchers’ analysis came about almost by accident. “I was looking at that paper for a different study,” he says, “and I came across [Korcek’s] work, which hadn’t been verified either theoretically or experimentally. … [We] decided to see if we could explain his observations by throwing quantum mechanical tools at the problem.”

The researchers’s through analysis revealed in detail how the reaction takes place. Remarkably, Korcek’s predictions were on par, albeit  part of the process differs slightly from Korcek’s original hypothesis. Green points out that because this is an entirely new type of reaction, it opens the door to research on other variations.

“Once you discover a new type of reaction, there must be many similar ones,” he says.

“It’s very odd to have so many reactions at once in such a small molecule,” Green adds. “Now that we know that can happen, we’re searching for other cases.”

What’s so special about this reaction? First of all, it’s a newly fully described chemical reaction. Understanding in full detail what goes on at a molecular level in a compound subjected to various environmental stimuli is paramount to science. Regarding practical applications, biofuel technology might be the first to benefit from the new findings. Various kinds of biofuels oxidize differently — sometimes producing toxic or corrosive byproducts —  and by applying this new found understanding of degradation following oxidation might help scientists pin down the best fuel types worth pursuing.

Like all organic matter, the human body suffers oxidation as well contributing to the tissue damage and aging.

Anthony Dean, dean of the College of Applied Science and Engineering at the Colorado School of Mines, who was not involved in this work, says, “A particularly nice aspect of this work is to then consider how this finding might be applicable to other systems. In a broader context, this combined effort by two very prominent research groups illustrates the power and potential for electronic structure calculations [in] quantitatively important problems in chemical kinetics.”

Klippenstein adds, “As a result of this clear exposition and the high level of theory that was applied, I believe this work will be widely accepted immediately. I certainly am already convinced by their conclusions.”

J. Am. Chem. Soc., 2013, 135 (30), pp 11100–11114 , DOI: 10.1021/ja4034439