Unique Superacid is a Million Times Stronger than Sulfuric But Noncorrosive

Traditional superacids—any acids stronger than 100% sulfuric acid—are prized by laboratory chemists for their strong protonating abilities, but are so corrosive in solution that they often destroy the molecules they have just protonated. Now, chemists at the University of California (UC), Riverside have come up with a superacid that is noncorrosive; they have used it to protonate fullerenes (C₆₀), producing the previously elusive "buckeyball" cation, HC₆₀⁺.

The new superacid, reported in the July 7 issue of Science by UC, Riverside chemist Christopher A. Reed and colleagues, is a protonated form of the cage-like molecule called carborane. Its formula is H(CB₁₁H₆X₆), where X is either a chlorine or bromine atom. Chemists had tried for years to prepare this molecule, but it wasn't until the UC team worked in completely dry conditions that they succeeded in making it.

While the new superacid is some one million times stronger than concentrated sulfuric acid, it lacks the two common drawbacks of other superacids: the strong nucleophilicity of their anions, which causes them to form unwanted complexes in solution; or their extreme oxidizing power, which causes desired molecular products to decompose.

As described in their current paper, members of Reed's group have gotten their new superacid to form the HC₆₀⁺ ion, which had long been sought but was impossible to prepare with conventional superacids. This ion is both stable in solution and in the solid state, they report.

By overcoming some of the major limitations of superacids, the H(CB₁₁H₆X₆) superacid has "potentially wide application," the authors write. The carborane derivative may be useful in the oil refining industry to upgrade octane rating of fuels, they suggest. Or it may allow chemists to isolate normally short-lived reaction intermediates in solution, giving them insight into reaction mechanisms.

For more information, contact Christopher A. Reed, University of California, Riverside, at 909-787-5716.

By Gordon Graff