Gasoline plays a major role in our daily lives as fuel for both large and small engines alike. The environmental impact of burning fossil fuels has led to initiatives to minimize these effects. One of the most well-known initiates is the addition of corn-derived ethanol to fuels to increase octane levels while reducing the overall consumption of fossil fuels. In this experiment, students will extract ethanol from commercial gasoline and characterize the resulting solutions using NMR spectroscopy.

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The octane number of fuels is important in defining the resistance to spontaneous ignition of fuels which can cause “knocking” and damage to an engine. The octane ratings were developed using the isooctane molecule as the benchmark against which a fuel’s resistance to self-ignition is measured and assigned an octane rating of 100 relative to the spontaneously ignition prone heptane with a value of 0. Commercial fuels, which contain a complex mixture of numerous hydrocarbons are measured against the isooctane standard and assigned an octane number. Additives to boost the octane rating are typically expensive to produce, but ethanol, with an octane rating of 109 is an exception as it is readily produced from corn. As a result, ethanol has been added to most consumer fuels since the early 2000s.

Nuclear Magnetic Resonance (NMR) is a powerful analytical tool capable of providing both qualitative (what is this) and quantitative (how much is there) data quickly and non-destructively. NMR is used extensively in a number of research and industrial applications including new molecule synthesis, pharmaceuticals, petrochemical, and teaching to determine chemical structure and quantitate mixtures.

In this lab, students extract ethanol from commercial gasoline and analyze the resulting solutions with the picoSpin NMR spectrometer to determine the chemical structure of ethanol. For additional difficulty, the NMR can be used to measure the amount of ethanol in the original sample and any residual water in the extracted ethanol.

About the author 

John Frost, Ph.D., is a chemist at Thermo Fisher Scientific, Rhinelander, WI. He received his Master's degree in organic chemistry at Michigan Technological University, studying the effects of mono-substituted amides on the intramolecular sulfoxide electrophilic sulfenylation reaction. He received his Ph.D. in analytical and physical chemistry from the University of Wisconsin-Milwaukee, developing a new long-path length spectroscopic technique. John is an alumnus of the Center for Workshops in the Chemical Sciences and an American Chemical Society Science Coach for Overland High School in Aurora, CO.

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