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Boron-based Carborane Acid
The strongest Brønsted-Lowry acid is the boron-based carborane acid, also known simply as carborane acid (1 ). This superacid is known to be one million times stronger than sulfuric acid whose pKa value is 1.92. 〔Olah, G. A.; Prakash, G. K. S.; Sommer, J.; Molnar, A. (2009). Superacid Chemistry (2nd ed.). Wiley. p. 41. ISBN 978-0-471-59668-4.〕 As defined in chemistry, a Brønsted-Lowry acid’s strength corresponds with its ability to release a hydrogen ion (2 ). Carborane acids differ from classic superacids by giving high superacidity to weakly basic organic solvents. It does so without the complication of adding a strong Lewis acid. 〔Reed, Christopher. “Carborane acids. “New ‘strong yet gentle’ Acids For Organic and Inogronic Chemistry.” Advance Article (February 2005). Accessed February 13, 2015. 〕 In solution, boron-based carborane acid releases a proton very easily therefore drastically increasing acidity while giving an extremely basic anion: the chlorinated carba-closo-dodecaborate anion, ()-.
Despite being the strongest acid, the boron-based carborane acid is also known as the gentlest acid, making it the least corrosive acid. 〔Reed, Christopher A. “The Strongest Acid.” Chemistry in New Zealand (October 2011): 174-179. Accessed February 13, 2015.〕 Whereas conventional strong acids decompose C60 fullerenes only at low temperatures, carborane acid has the ability to protonate fullerenes at room temperature to yield an isolable salt. 〔Juhasz, M.; Hoffmann, S.; Stoyanov, E.; Kim, K.-C.; Reed, C. A. (2004). "The Strongest Isolable Acid". Angewandte Chemie International Edition 43 (40): 5352–5355. doi:10.1002/anie.200460005. PMID 15468064〕 Its acidic yet gentle duality allows the protonation of fullerenes without fully decomposing them. 〔 〔Reed, C. A. (2005). “Carborane acids. “New ‘strong yet gentle’ Acids For Organic and Inogronic Chemistry.” Chemical Communications 2005 (13): 1669–1677. doi:10.1039/b415425h. PMID 15791295.〕 This property is also what makes carborane acid the first superacid that can be stored in a bottle.〔Hopkin, M. (2004, November 1). World's strongest acid created. Retrieved March 3, 2015, from http://www.nature.com/news/2004/041115/full/news041115-5.html〕 Other comparable superacids, such as fluorosulfuric acid or hydrofluoric acid, readily donate protons in a similar way to carborane acid, but leave behind incredibly corrosive conjugate bases that are highly reactive and can even degrade glass by breaking down the protonated O-Si-O bond.〔Juhasz, M.; Hoffmann, S.; Stoyanov, E.; Kim, K.-C.; Reed, C. A. (2004). "The Strongest Isolable Acid". Angewandte Chemie International Edition 43 (40): 5352–5355. doi:10.1002/anie.200460005. PMID 15468064
〕 Carborane acid's remarkably stable conjugate base allows it to be contained easily because it does not react in this manner. 〔Hopkin, M. (2004, November 1). World's strongest acid created. Retrieved March 3, 2015, from http://www.nature.com/news/2004/041115/full/news041115-5.html〕
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