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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Quo Vadis, Superacidity of Neutral Brønsted Acids? The Challenge for the Fluorine Chemistry Peeter Burk, Ivo Leito, Ivar Koppel, Ilmar Koppel University of Tartu
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Definition of Gas-Phase Acidity and Basicity
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Connection Between Gas-Phase Acidity and Acidity in Solution
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics 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
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Superacids by ‘Brute Force’
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Superacids by ‘Brute Force’
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics A Few Milestones of G acid CH 4 408.5 NH 3 396.1 H 2 394.2 C 6 H 6 390.1 MeOH374.0 HF365.7 SiH 4 363.8 PH 3 360.7 LiH351.1 H 2 S344.8 MeCOOH341.7 PhOH342.3 PhCOOH331.7 HONO330.4 HCl328.0 (CF 3 ) 3 CH326.8 HNO 3 317.8 HBr318.8 H o 312.5 HI308.9 Tf 2 CH 2 301.5 H 2 SO 4 302.2 CF 3 SO 3 H299.5 Tf 3 CH289.0 (C 4 F 9 SO 2 ) 2 NH 284.1 zeolites290-255
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Lewis Acids and Bases A + D: AD e.g.: HF: + BF 3 HBF 4 HF: + SbF 5 HSbF 6 HSO 3 F + SbF 5 “Magic acid”
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Koppel et al., JACS, 2000, 122, 5114-5124 DFT B3LYP/6-311+G**
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Yagupolskii Principle
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Yagupolskii Principle G acid = ~260 kcal/mol
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Yagupolskii Principle Koppel et al., J.Chem.Soc. Perkin 2 2001, 230-234 pK a (DMSO)GP 16.3 8.0 3.2 pK a = 14.1 pK a = 25
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Generalization of Yagupolskii Principle Why only =NSO 2 CF 3 substitution? =NX 1 =CX 1 X 2 =PX 1 X 2 X 3 =SX 1 X 2 X 3 X 4 =ClX 1 X 2 X 3 X 4 X 5 X = SO 2 F, SO 2 CF 3, CN, etc. Koppel et al., JACS, 2002, 124, 5594-5600
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Generalization of Yagupolskii Principle Acidifying Effects of Different Yagupolskii-Type Substituents on the Acidity of CH 3 C(=X)H (B3LYP/6-311+G**) Koppel et al., JACS, 2002, 124, 5594-5600 10 91
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics 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
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carboranes The strongest acids The least coordinating anions The 1-carba-closo-dodecaborate anion CB 11 H 12 – : Koppel et al., JACS, 2000, 122, 5114-5121
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane anion CB 11 H 12 – : The Distribution of Negative Charge
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane anion CB 11 F 12 – : The Distribution of Negative Charge 10 68 Times stronger than H 2 SO 4
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carboranes: The Site of Protonation CB 11 F 12 – : On substituents
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane acids: the Acidity (DFT B3LYP 6-31+G*) and Site of Protonation
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane Anions The acid CB 11 (CF 3 ) 12 H is expected to have G acid < 200 kcal/mol That is: 10 80 times stronger than H 2 SO 4 ! CB 11 (CF 3 ) 12 –
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Alkoxymetallate-, Aryloxymetallate- and Teflate-based Acids HM[OR F ] n e.g. HAl[OCF 3 ] 4 M = B, Al, Nb, Ta, La, etc. HM[OAr F ] n e.g. HAl[OC 6 F 5 ] 4 M = B, Al, Nb, Ta, La, etc. HM[OTeF 5 ] 6 e.g. HTa[OTeF 5 ] 6 M = B, Al, Nb, Ta, La, etc.
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Example: Alkoxyaluminate-based Acid HAl[OCF 3 ] 4 : G acid = 240.6 kcal/mol H+H+ -
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Acidities of Carborane Acids
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Spontaneous Proton Transfer in the Gas Phase K 2 O + H + = K 2 OH + G=324.6 ClO 4 - + H + = HClO 4 G=293.3 K 2 O + HClO 4 = K 2 OH + ClO 4 - G=119.4 K 2 OH + + ClO 4 - = K 2 OH + · ClO 4 - G=88.0
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics 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
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics 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
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics 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...
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University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Application of Superstrong Acids and Their Salts Organic synthesis Diels-Alder reactions Electrophilic Aromatic Substitutions Friedel-Crafts reactions Ionic liquids
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