Is There an Acid Strong Enough to Dissolve Glass?

Home , Hammett acidity function, Hydrofluoric acid, Magic acid, Methanium, Superacid

ARTICLE Is there an acid strong enough to dissolve glass? – Superacids

For anybody who watched cartoons growing up, the word unit is based on how acids behave in water, however as acid probably springs to mind images of gaping holes being very strong acids react extremely violently in water this burnt into the floor by a spill, and liquid that would dissolve scale cannot be used for the pure ‘common’ acids (nitric, anything you drop into it. The reality of the acids you hydrochloric and sulphuric) or anything stronger than them. encounter in schools, and most undergrad university Instead, a different unit, the Hammett acidity function (H0), courses is somewhat underwhelming – sure they will react is often preferred when discussing superacids. with chemicals, but, if handled safely, where’s the drama? A superacid can be defined as any compound with an People don’t realise that these extraordinarily strong acids acidity greater than 100% pure sulphuric acid, which has a do exist, they’re just rarely seen outside of research labs Hammett acidity function (H0) of −12 [1]. Modern definitions due to their extreme potency. These acids are capable of define a superacid as a medium in which the chemical dissolving almost anything – wax, rocks, metals (even potential of protons is higher than it is in pure sulphuric acid platinum), and yes, even glass. [2]. Considering that pure sulphuric acid is highly corrosive, you can be certain that anything more acidic than that is What are Superacids? going to be powerful. What are superacids? Its all in the name – super acids are intensely strong acids. These acids knock conventional There is a number of organic superacids, such as triflic acids out of the park when it comes to their acidity. acid (trifluoromethanesulphonic acid) or fluorosulphuric acid, both of which are around 1000 times stronger than To understand superacids we first have to go back to sulphuric acid. basics – An acid’s acidity is commonly described by its pH, which is the unit most scientists are familiar with. The pH

For Research Use Only. Not for use in diagnostic procedures. © 2016 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific and its subsidiaries unless otherwise specified.

Art_Superacids_2016 Fluoroantimonic acid (H2FSbF6), (first prepared in 1927) is Because of this superacids are good at forming a relatively even more powerful, being 1016 times stronger than 100% stable environment in which to study unstable + sulfuric acid and producing solutions with an H0 as low as carbocations, e.g. studies of the CH5 methanium ion [4]. –28 [1]. Fluoroantimonic acid is produced by carefully combining hydrogen fluoride (HF) and antimony What are superacids used for?

pentafluoride (SbF5). Fluoroantimonic is powerful enough Despite their obvious use in research, for the formation and to eat its way through glass, meaning it must be stored in study of reactive carbocations, superacids also have a specially produced fluorine polymer coated containers. number of important industrial uses. Some of these include their use as catalysts in the petrochemical industry during One of the most powerful superacids known is “magic primary thermal cracking to produce high octane gasoline acid”, which is the result of mixing antimony pentafluoride fractions. They also have uses in the production of high

(SbF5) and fluorosulfonic acid (FSO3H). It gained the name density polymers. “magic” because of its ability to dissolve anything, even inert hydrocarbons. This was first noticed because it’s Despite this usefulness, it must be remembered that creators observed that it was able to fully dissolve a paraffin superacids are extremely corrosive, toxic and powerful wax candle - which astounded them so much that they reagents with the potential to be an environmental hazard. thought someone was playing a magic trick. More recent industrial processes are using superacids in the solid phase as catalysts for many reactions such as; This ability to dissolve wax is (somewhat counterintuitively) esterification, isomerisation, alkylation, polymerisation, even more impressive than their ability to dissolve glass. cracking and more [5]. Wax is extremely inert, and getting anything to react with it is an achievement in itself. Superacids have pushed the boundaries of organic chemistry and allowed important research into carbonium Why are superacids special? ions and they have also made an important contribution For anybody who watched cartoons growing up, the word unit is based on how acids behave in water, however as Superacids are on a different playing field than water-based to chemical engineering in the petrochemical and acid probably springs to mind images of gaping holes being very strong acids react extremely violently in water this acids because they can form their own solvent and can also polymer industries. burnt into the floor by a spill, and liquid that would dissolve scale cannot be used for the pure ‘common’ acids (nitric, be used in organic solvents. anything you drop into it. The reality of the acids you hydrochloric and sulphuric) or anything stronger than them. The Alfa Aesar™ product line contains several different encounter in schools, and most undergrad university Instead, a different unit, the Hammett acidity function (H0), Their acidic strength comes from their ability to make bronsted superacids for use in specialist applications. courses is somewhat underwhelming – sure they will react is often preferred when discussing superacids. protons available for reaction. In water based acids protons These include hydrogen bromide, hydrofluoric acid, with chemicals, but, if handled safely, where’s the drama? are hydrated, meaning they are stabilised by surrounding hexafluorophosphoric acid and tetrafluoroboric acid. A superacid can be defined as any compound with an water molecules. The protons in superacidic solutions are These acids come in a variety of concentrations for a variety People don’t realise that these extraordinarily strong acids acidity greater than 100% pure sulphuric acid, which has a considered “naked”, meaning there is nothing stabilising of applications. To find out more about the different, do exist, they’re just rarely seen outside of research labs Hammett acidity function (H0) of −12 [1]. Modern definitions them, making them extremely reactive. The protons in high-quality, inorganic acids in the Alfa Aesar catalogue due to their extreme potency. These acids are capable of define a superacid as a medium in which the chemical superacids are much more mobile, hopping from one acidic please visit their website. www.alfa.com/en/inorganic-acids dissolving almost anything – wax, rocks, metals (even potential of protons is higher than it is in pure sulphuric acid anion to another, meaning they are always available platinum), and yes, even glass. [2]. Considering that pure sulphuric acid is highly corrosive, for reaction. you can be certain that anything more acidic than that is What are Superacids? going to be powerful. These highly reactive protons are the reason superacids are What are superacids? Its all in the name – super acids are excellent at producing carbocations (protonated organic intensely strong acids. These acids knock conventional There is a number of organic superacids, such as triflic molecules) because they can force a positive proton onto acids out of the park when it comes to their acidity. acid (trifluoromethanesulphonic acid) or fluorosulphuric inert species which would not readily accept one under acid, both of which are around 1000 times stronger than normal circumstances [3]. It is for this reason that magic To understand superacids we first have to go back to sulphuric acid. acid is capable of dissolving candles. basics – An acid’s acidity is commonly described by its pH, which is the unit most scientists are familiar with. The pH

Art_Superacids_2016 References 1. Hall, N. F.; Conant, J.B. “A Study of Superacid Solutions” Journal of the American Chemical Society 1927, 49, (12), 3062–70

2. Olah, G. A. “Crossing Conventional Boundaries in Half a Century of Research” Journal of Organic Chemistry 2005, 70, (7), 2413–2429

3. Olah, G. A.; Schlosberg R. H. “Chemistry in Super Acids. I. Hydrogen Exchange and Polycondensation of Methane and Alkanes in FSO3H–SbF5 (“Magic Acid”) Solution. Protonation of Alkanes and the Intermediacy of CH5+ and Related Hydrocarbon Ions. The High Chemical Reactivity of “Paraffins” in Ionic Solution Reactions” Journal of the American Chemical Society 1968, 90, (10), 2726–7

4. Golam Rasul, G. K.; Prakash, S.; Olah, G. A. “Comparative study of the hypercoordinate carbonium ions and their boron analogs: A challenge for spectroscopists” Chemical Physics Letters 2011, 517, (1–3), 1–8

5. Khalaf, H. A. “Solid Superacid Catalysts and Their Applications” American Journal of Materials Science 2015, 5(2A), doi:10.5923/s.materials.201501

Art_Superacids_2016 For more information, please visit www.alfa.com/en/inorganic-acids

Art_Superacids_2016