Joseph Francisco

When Thomas Midgley, Jr. first invented chlorofluorocarbons, they appeared to be safe. Midgley's public demonstrations where he safely inhaled CFCs seemed to prove this. In the 1930s no one knew about the strange chemistry that went on in the upper atmosphere, or how important stratospheric ozone was. Today some vilify Midgley while others defend him. But leaving the issue of his guilt or innocence aside, a lot of things can be learned from the story of CFCs, lessons that can teach us how to avoid future fiascos of this sort. This is what the work of scientists like Joseph Francisco is all about.

Francisco began encountering chemistry when he was in high school, first while working as an assistant in a pharmacy in Beaumont, Texas. At the time young Francisco might have seemed more likely to become a zoologist than a chemist. His large collection of pets included dogs, cats, rabbits, and chickens, all of which needed to be fed. To pay for all the critter chow he went to work assisting the local pharmacist. The curious Francisco was eager to learn as much as he could from his boss about medicines and pharmacology. His involvement in chemistry grew when he spent a summer learning chemistry (and physics) to create a good science fair project during his senior year. His entry, a homemade gas chromatograph, took third place at the state science fair.

As an undergraduate at the University of Texas he did research unraveling the molecular structure of compounds and designing as well as synthesizing superconducting materials. While he was earning his doctorate at the Massachusetts Institute of Technology he began using lasers to study chemical reactions. This kind of research was new in the late 1970s and he had to travel to Australia to learn the new techniques from experts down under.

Gone in sixty microseconds

After graduate school Dr. Francisco became a professor of chemistry, first at Wayne State University in Detroit, then moving to Purdue University in West Lafayette, Indiana. Throughout the 1990s, he and his collaborators and students, set about examining the finest details of the reactions thought to take place in the upper atmosphere. Take a look at the reaction cycle by which a CFC destroys ozone, that you see below. Notice that it isn't the CFC itself that destroys the ozone, but the Cl and ClO that are produced when the CFC breaks down in the stratosphere.

We know that CFCs break down and produce Cl and ClO. That's what Mario Molina showed us. But what about the potential replacements for CFCs? What do they produce when they break down? Do their decomposition products destroy ozone? Do they have other harmful effects? These are the kinds of question Dr. Francisco has been trying to answer.

Studying the decomposition products of new refrigerants isn't easy. First, one has a lot of compounds to sift through. Second, the conditions of the upper atmosphere have to be simulated in the laboratory to study how any compound breaks down way up there. Third, the decomposition products often react quickly after they form, making them hard to identify, let alone to study.

Scientists like Dr. Francisco often use computer models to help them sift through the compounds, both potential refrigerants and their decomposition products, to find which ones need to be studied. Then the compounds are studied under simulated upper atmospheric conditions. This is the same way Mario Molina carried out his studies on CFCs. But studying those fleeting decomposition products requires some clever tricks.

Remember those lasers that Dr. Francisco traveled to Australia to learn how to use? Very short, rapid laser pulses can be used to "shoot a movie" of a chemical reaction. Here's how it works: We can identify compounds by how they interact with different kinds of light. Every compound absorbs specific wavelengths of light and lets other pass through. That is, each compounds has a unique spectrum of light it absorbs. The use of light to identify compounds in this way is called spectroscopy. By observing the spectrum of a chemical reaction mixture as it happens can reveal the identity of short-lived compounds that are formed in chemical reactions, but react quickly to form other compounds. These short-lived compounds are called reactive intermediates.

Using lasers, scientists like Dr. Francisco can take a rapid series of spectra, and the result is a sort of motion picture of the chemical reaction taking place. Looking at the spectra they can identify reactive intermediates that we might not be able to spot otherwise.

Don't make the same mistake twice

Reactive intermediates have to be studied, because they are so important in the reactions that destroy ozone. In the late 1960s and early 1970s, Mario Molina made detailed studies of the reactions that CFCs undergo in the stratosphere. Now that we know that CFCs destroy ozone, we have to find new refrigerants. But rather than discover too late that a new refrigerant causes some unforeseen ecological disaster, scientists today are trying to find out what might happen to new refrigerants in the upper atmosphere before they are put into use.

Among his other research activities, Dr. Francisco has spent nearly a decade investigating the reactive intermediates produced by reactions of potential refrigerants. A lot of his effort has gone into studying hydrofluorocarbons (HFCs) and fluorocarbon ethers. So far, a lot of the studies on HFCs show that they are unlikely to destroy ozone. By studying such reactive intermediates likely to be produced by HFCs in the atmosphere, Dr. Francisco has found them unlikely to damage ozone.

Some of the strange reactive intermediates that can be
produced by the degradation of HFCs in the atmosphere.

Things don't look as good for the fluorocarbon ethers. What is a fluorocarbon ether, you ask? An ether is a compound whose molecules contain a carbon-oxygen-carbon chain, such as dimethyl ether, seen below on the left.

dimethyl ether	trifluoromethyl methyl ether

A fluorocarbon ether is just an ether that contains fluorine atoms. You can see one above on the right. The bad news about these compounds isn't that they might hurt ozone. They probably wouldn't. The problem with these molecules is that when Dr. Francisco studied them spectroscopically, he found out that they absorb infrared light at just the right wavelengths to make them potential greenhouse gases. This is just the kind of thing we need to know before we start using any new refrigerant.

Next: What Is a Refrigerant?

Joseph S. Francisco — find out about Dr. Francisco's work firsthand on his faculty Web page at Purdue University.

Nobel Prize in Chemistry 1999 — learn about the work of Egyptian chemist Ahmed H. Zewail. Zewail is a pioneer in the field of "femtochemistry," that is, using pulsed lasers to make "motion pictures" of chemical reactions to study how they take place and the short-lived molecules that exist during reactions, from the Nobel Foundation.

References

Good, D. A., Francisco, J. S., and DeMore, W. "Structure and Vibrational Spectra of CFC Substitutes: An Experimental and Ab Initio Study of Fluorinated Ethers CHF₂OCF₃ (E125), CHF₂OCHF₂ (E134), and CH₃OCF₃ (E143)" Journal of Physical Chemistry 1998, 102, 1854-1864.

Kessler, James H., Kidd, J.S., Kidd, Renée, and Morin, Katherine. Distinguished African American Scientists of the 20th Century. Phoenix: The Oryx Press, 1996.