Magic Acid or HSO3 F-SbF5 (Fluorosulfuric acid-antimony pentafluoride) is not just a fancy name; it has more than a few amazing properties and a discovery story that is, well, magical.
It was a December evening half of a century ago at a Christmas party at George A. Olah’s laboratory. The room full of chemists could not, however, simply enjoy the festivity of the season. A candle left over from the cake was placed in the chemical compound we now know as Magic acid, and the candle disappeared like magic right before their eyes. A quick trip to the NMR revealed that the parafin wax was now a tert-butyl cation solution. The saturated hydrocarbons had been protonated! (5)
This party discovery had many real world applications that I will get to later, but, first, let’s talk a little about the chemistry behind the magic.
Acids can be defined several ways. Arrhenius Acids form H3O+ in water. Bronsted-Lowry acids are proton donors and Lewis acids are electron pair acceptors. (4) HSO3F is a strong Bronsted-Lowry acid, but when it is combind with the Lewis acid SbF5, it becomes a superacid. (2) Superacids include all protic acids that are stronger than 100% sulfuric acid. (5) They are so acidic that the traditional method of measuring an acid’s hydrogen ion concentration to determine acidity (pH) will not work. Instead, the Hammett acidity function is used in which Ho = pKBH+ – log([BH+]/[B]). (2) Magic acid has an Ho value of about -23. (5)
So, what can a superacid like Magic Acid do?
Magical things! The large complex of fluoroanions in Magic Acid help disperse the negative charge making it a really strong acid. It can protonate really weak bases, even saturated hydrocarbons. Straight chained carbon chains can be converted to branched chains and carbon-carbon bonds can be formed at low temperatures. (2)
It is magical and exciting, but why do we care?
One word: gasoline. The crude oil that is obtained through drilling is not a very good energy source. It has to go through a long line of chemical changes before it can be pumped into your car. Catalytic cracking and polymerization are two important processes that require some sort of catalyst. (3) Traditionally, HF has been the catalyst of choice due to its high activity at low temperatures, but superacids, especially Magic Acid, have been put forth as the Earth and health friendly alternative. (6)
Wait … What is unsafe about hydrofluoric acid?
Unfortunately, the answer is that almost everything about HF is unsafe. It is incredibly corrosive. It not only burns the skin, it penetrates it causing systemic poisoning. When inhaled, it causes pulmonary endema and, when it gets in your systemic circulation, it binds to divalent cations resulting in electrolyte imbalance. Not to mention, it interferes with both glycolysis and oxidative phosphorylation. (1) Basically, it is best to put as much space between you and this nasty compound. So, are the risks worth the convenience of easy-made gasoline that fuels our way of life? I don’t think so, and I think that the public, with the right information, would agree.
Good thing we have Magic Acid to save the day. Right?
Not so fast. Magic Acid is a superacid, but it is not a super hero. Magic Acid has been hailed as the cure to all of gasoline’s problems. It has been called an “environmentally sound and stable operation” and has been praised for its ability to “decrease the environmental and safety hazards associated with using highly volatile HF itself” by Olaf himself (2;5). These statements are all true. Magic Acid is better than HF, but it is not without its own shortcomings. Most importantly, it actually forms HF when it comes into contact with water. What Olaf and other contemporaries are arguing is that Magic Acid is a step up from HF and, therefore, a good option.
But is better good enough?
That, of course, is a matter of opinion, but I don’t think that better is good enough, especially when there are options that can eliminate HF from the equation altogether. (Solid acids are one option that has been explored. (6)) Compromising health, safety, and the environment for a cheaper or easier option is simply not acceptable. Science can create some magical things, but the potential for these extraordinary compounds to cause unnecessary harm to the planet needs to be carefully studied.
1. Blodgett, David W., Suruda, Anthony J., Crouch, and Barbara Insley. “Fatal Unintentional Occupational Poisonings by Hydrofluoric Acid in the United States.” American Journal of Industrial Medicine. 40.2 (2001): 215-220.
2. Liu, Paul Ih-fei. Energy, Technology, and the Environment. New York: Three Park Avenue, 2005.
3. Marton, Barry and Krapp, Kristine M. “Gasoline”. How Products are Made Volume 2. http://www.madehow.com/Volume-2/Gasoline.html
4. Miessler, Gary L. and Tarr, Donald A. Inorganic Chemistry. Boston: Prentice Hall, 2011.
5. Olah, George A. “Crossing Conventional Boundaries in Half a Century of Research. Journal of Organic Chemistry. 70.7(2005)
6. Sommer, J. and Jost, R. “Carbenium and carbonium ions in liquid and solid-superacid-catalyzed activation of small alkanes. Pure and Applied Chemistry. 72.12 (2000): 2309-2318.