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Definition of Gas-Phase Acidity and Basicity

Quo Vadis, Superacidity of Neutral Br ø nsted Acids? The Challenge for the Fluorine Chemistry Peeter Burk, Ivo Leito, Ivar Koppel, Ilmar Koppel University of Tartu. Definition of Gas-Phase Acidity and Basicity. Connection Between Gas-Phase Acidity and Acidity in Solution.

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Definition of Gas-Phase Acidity and Basicity

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  1. Quo Vadis, Superacidity of Neutral Brønsted Acids?The Challenge for the Fluorine ChemistryPeeter Burk, Ivo Leito, Ivar Koppel, Ilmar KoppelUniversity of Tartu

  2. Definition of Gas-Phase Acidity and Basicity

  3. Connection Between Gas-Phase Acidity and Acidity in Solution

  4. Strong Neutral Acids & Weak Anionic Bases - the common knowledge • Strong and Highly Polarizable Electron-Acceptor Substituents • Extensive Resonance Stabilization of the Anion / Delocalization of Negative Charge • Coplanarity of the Anion • Aromaticity and Antiaromaticity

  5. Superacids by ‘Brute Force’

  6. Superacids by ‘Brute Force’

  7. A Few Milestones of DGacid CH4 408.5 NH3 396.1 H2 394.2 C6H6 390.1 MeOH 374.0 HF 365.7 SiH4 363.8 PH3 360.7 LiH 351.1 H2S 344.8 MeCOOH 341.7 PhOH 342.3 PhCOOH 331.7 HONO 330.4 HCl 328.0 (CF3)3CH 326.8 HNO3 317.8 HBr 318.8 Ho 312.5 HI 308.9 Tf2CH2 301.5 H2SO4 302.2 CF3SO3H 299.5 Tf3CH 289.0 (C4F9SO2)2NH 284.1 zeolites 290-255

  8. Lewis Acids and Bases A + D:  AD e.g.: HF: + BF3 HBF4 HF: + SbF5 HSbF6 HSO3F + SbF5 “Magic acid”

  9. Koppel et al., JACS, 2000, 122, 5114-5124 DFT B3LYP/6-311+G**

  10. Yagupolskii Principle

  11. Yagupolskii Principle DGacid = ~260 kcal/mol

  12. Yagupolskii Principle pKa(DMSO) GP 16.3 DpKa=14.1 DpKa=25 8.0 3.2 Koppel et al.,J.Chem.Soc. Perkin 2 2001, 230-234

  13. Generalization of Yagupolskii Principle Why only =NSO2CF3 substitution? • =NX1 • =CX1X2 • =PX1X2X3 • =SX1X2X3X4 • =ClX1X2X3X4X5 X = SO2F, SO2CF3, CN, etc. Koppel et al., JACS, 2002, 124, 5594-5600

  14. Generalization of Yagupolskii Principle 1091 Acidifying Effects of Different Yagupolskii-Type Substituents on the Acidity of CH3C(=X)H (B3LYP/6-311+G**) Koppel et al., JACS, 2002, 124, 5594-5600

  15. New Paradigm for Design of Superstrong Acids - Weak Anionic Bases:Carborane Anions • No  Electrons • No “Loose” Lone Electron Pairs • 3-Dimensional -Aromaticity • Extensive Delocalization of Negative Charge • Pseudo-Icosahedral Symmetry

  16. Carboranes • The strongest acids • The least coordinating anions The 1-carba-closo-dodecaborate anion CB11H12–: Koppel et al., JACS, 2000, 122, 5114-5121

  17. Carborane anion CB11H12–: The Distribution of Negative Charge

  18. Carborane anion CB11F12–: The Distribution of Negative Charge 1068 Times stronger than H2SO4

  19. Carboranes: The Site of Protonation CB11F12–: On substituents

  20. Carborane acids: the Acidity (DFT B3LYP 6-31+G*) and Site of Protonation

  21. Carborane Anions CB11(CF3)12– The acid CB11(CF3)12H is expected to have DGacid < 200 kcal/mol That is: 1080 times stronger than H2SO4!

  22. Alkoxymetallate-, Aryloxymetallate- and Teflate-based Acids • HM[ORF]n e.g. HAl[OCF3]4 • M = B, Al, Nb, Ta, La, etc. • HM[OArF]n e.g. HAl[OC6F5]4 • M = B, Al, Nb, Ta, La, etc. • HM[OTeF5]6 e.g. HTa[OTeF5]6 • M = B, Al, Nb, Ta, La, etc.

  23. Example: Alkoxyaluminate-based Acid HAl[OCF3]4: DGacid = 240.6 kcal/mol - H+

  24. Acidities of Carborane Acids

  25. Spontaneous Proton Transfer in the Gas Phase K2O + H+ = K2OH+ G=324.6 ClO4- + H+ = HClO4G=293.3 K2O + HClO4 = K2OH+ ClO4-G=119.4 K2OH+ + ClO4- = K2OH+ · ClO4-G=88.0

  26. Application of Superstrong Acids and Their Salts • “Classical” Primary and Secondary Batteries (lead/acid, Ni/Cd, Fe/Ni, etc) • Fuel Cells • Lithium-Ion Batteries • Electric Double Layer Capacitors

  27. Application of Superstrong Acids and Their Salts Requirements: • High Conductivity • Thermal and Chemical Stability • Electrochemical Stability • Cheap • User- and Environment-Friendly • Non- Corrosive • Non Hygroscopic • Non- Coordinated Li+ • Low viscosity and high dielectric constant of the medium • Not “too large” anions

  28. Application of Superstrong Acids and Their Salts • Petrochemical refining and cracking of fuel (zeolites) • Organic synthesis • Reusable water-stable catalysts • Oligomerization of olefins, epoxides, ethers, etc. • Enantioselective synthesis Continued ...

  29. Application of Superstrong Acids and Their Salts • Organic synthesis • Diels-Alder reactions • Electrophilic Aromatic Substitutions • Friedel-Crafts reactions • Ionic liquids

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