Super Acids - Mureal

Super Acids

1. Superacids Hammett acidity Function

2. According to the classical definition, a super acid is an acid with an acidity greater than that of 100% pure sulfuric acid, which has Hammett acidity function of -12. According to the modern definition, a super acid is a medium in which the chemical potential of the proton is higher than in pure sulfuric acid.

3. More efficient proton donor than pure sulphuric acid. Viscous, corrosive liquid. 10 18 times more acidic than sulphuric acid. Formed when powerful Lewis acid is dissolved in a powerful Bronsted acid.

4. HAMMETT ACIDITY FUNCTION: Is a measure of acidity that is used for very concentrated solution of strong acid, including super acid. Proposed by the physical organic chemist Louis Plack Hammett. H = pK BH + log [B]/[BH + ]

5. EXAMPLES Fluorosulphuric acid: (H = -15.1) Is a inorganic compound with chemical formula HSO 3 F Strongest acid commercially available. It is a tetrahedral molecule. Colourless liquid, although commercial samples are yellow. It is prepared by reaction of HF and sulfur trioxide. SO 3 + HF HSO 3 F

6. 2. Carborane: (H < -18) Chemical formula- H(CXB 11 Y 5 Z 6 ) (X,Y,Z =H,Akl, F, Cl, Br, CF 3 ) These are a class of super acid, some of which are estimated to be at least one million times stronger than pure sulphuric acid. Strongest known Bronsted acid.

7. 3. Fluoroantimonic acid (H between -21 and -23) Organic compound with chemical formula H 2 FSbF 6 . It is extremely strong acid. Prepared by treating hydrogen fluoride with antimony pentafluoride in a 2:1 ratio This results in the formation of fluoronium ion. 2 HF + SbF 5 SbF 6 - + H 2F + The extreme Acidity of fluoroantimonic acid is because of fluoroantimonic ion.

8. 4. Triflic acid (H = - 14.9) Also known as trifluoromethanesulfonic acid. Is a sulfonic acid With chemical formula CF 3 SO 3 H. It is hygroscopic, colorless, slightly viscous liquid and soluble in polar solvents. It is produced industrially by electrochemical fluorination of methane sulfonic acid. . CH 3 SO 3 H + 4HF CF 3 SO 2 F + H 2 O + 3H 2 CF 3 SO 2 F is hydrolyzed. It can also be produced by oxidation of trifluoromethylsulfenylchloride. CF 3 SCl + 2Cl 2 +3H 2 O CF 3 SO 3 H + 5HCl It is mainly used in research as a catalyst in esterification.

9. 5. Magic acid (H = -19.2) It consists a mixture of fluorosulpuric acid and antimony pentafluoride in 1:1 ratio. It is conjugate Bronsted- Lewis super acid system developed by George Olah. It has been used to stabilize carbonation and hypercoordinated carbonium ions in liquid medium. It can proton weak bases including methane, xenon, halogens and molecular hydrogen.

10. APPLICATIONS: In petrochemist, super acidic media are used as catalysts, especially for alkylation. Typical catalysts are sulfated oxides of titanium or zirconium specially treated alumina or zeolite. Solid acids are alkylation benzene with ethene and propene.

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