The Strongest Isolable Acid

Juhasz, Mark; Hoffmann, Stephan P.; Stoyanov, Evgenii S.; Kim, Kee‐Chan; Reed, Christopher A.

doi:10.1002/ange.200460005

Cited by 37 publications

(30 citation statements)

References 17 publications

(15 reference statements)

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“…[13][14][15][16][17] These bands are assigned to combination modes because they do not belong to the fundamental transitions of benzene. 18 Consideration of the IR spectrum of the triflate anion corroborates the assignment of structure 3 to the [H 3 O][CF 3 -SO 3 ] ion pair. The proposed bidentate H-bonding of the triflate anion in 3 can be contrasted to monodentate H-bonding in the tri-n-octylammonium triflate structure.…”

Section: Resultsmentioning

confidence: 72%

“…On the other hand, the spectrum of the triflate ion in [H 3 O][CF 3 SO 3 ] more closely approaches a structure having C 3V symmetry. As shown in Table 2, the set of bands is similar to those of [NH 4 ][CF 3 SO 3 ], whose solid-state structure is known from X-ray data to have more or less equivalent H-bonding to all three O-atoms.…”

Section: Resultsmentioning

confidence: 99%

“…5,20 In solution spectra, the two OH stretching vibrations of the water molecules are usually overlapped, giving one broad band. 5 3 ], however, two well-resolved broad bands at 3460 and 3050 cm -1 are apparent and the δHOH band at 1739 cm -1 is distinctly asymmetric (see Figure 2). These peculiarities can be understood in terms of structure 5, where one end of the H 5 O 2 + ion is strongly ion-paired and the other end is more weakly H-bonded to DCE solvent molecules.…”

Section: Resultsmentioning

confidence: 99%

“…Delocalization of charge into the N-S bonds increases their multiplicity and also affects the SdO bonds. This effect is much more dramatic in the [Oct 3 NH][N(SO 2 CF 3 ) 2 ] salt, representing complete proton transfer. The νN-S frequency is higher by 207 cm -1 and the ν as SO 2 frequency is lower by 103 cm -1 relative to monomeric acid (Table 3).…”

Section: Resultsmentioning

confidence: 99%

“…Trifluoromethylsulfonyl imides have attracted attention recently as the strongest gas-phase acids measured to date. 2,3 Bis(trifluoromethylsulfonyl) imide is only a few orders of magnitude weaker than triflic acid when pK a values are measured in acetic acid solution. 4 The neat acid strength of (CF 3 -SO 2 ) 2 NH cannot be compared to that of triflic acid using the familiar H 0 scale because (CF 3 SO 2 ) 2 NH is a solid, not a liquid.…”

Section: Introductionmentioning

confidence: 99%

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A Strong Acid that Does Not Protonate Water

2004

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The nature of solvated acids in benzene and chlorinated hydrocarbon solvents is sensitively revealed by IR spectroscopy. Two similarly strong, structurally related acids, triflic acid (CF 3 SO 3 H) and the N-H acid bis-(trifluoromethylsulfonyl) imide ((CF 3 SO 2 ) 2 NH), behave quite differently toward water in these media. Triflic acid protonates water at the one-equivalent level to give the hydronium ion, H 3 O + . By contrast, bis(trifluoromethylsulfonyl) imide forms a simple hydrate, (CF 3 SO 2 ) 2 NH‚‚‚OH 2 , even with water at the twoequivalent level. The difference arises from the differing abilities of the conjugate base anions to engage in H-bonding and ion pairing. It illustrates how acidity in low-dielectric media is critically dependent on the nature of the conjugate base anion. νO-H and νN-H stretching frequencies indicate that the H-bonding acceptor ability for solvents toward acidic protons increases in the order carbon tetrachloride < benzene ∼ 1,2-dichoroethane < water. With benzene, a marked tendency for acidic protons to H-bond to the π-face of the arene ring is noted and an IR signature of this solvation mode is observed.

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Section: Resultsmentioning

confidence: 72%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Strong Acid that Does Not Protonate Water

2004

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Putting tert‐Butyl Cation in a Bottle

Kato

Reed

2004

Angewandte Chemie

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Angewandte Chemie CommunicationsSimple alkyl carbocations such as the tertbutyl cation can be isolated and stored (in a bottle) as stable salts at room temperature when partnered with inert carborane anions. The "Me + " reagents CH 3 (CHB 11 H 5 X 6 ), X = Cl or Br, are sufficiently powerful electrophiles that they can abstract hydride from hydrocarbons at or below room temperature. For more information, see the Communication by C. A. Reed and T. Kato on the following pages.

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Superacidity of Boron Acids H₂(B₁₂X₁₂) (X=Cl, Br)

Avelar¹,

Tham²,

Reed³

2009

Angewandte Chemie

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Keywords arenium ions; carboranes; IR spectroscopy; superacidic systems; weakly coordinating anions The finding that monoprotic carborane acids of the type H(CHB 11 X 11 ) (X=Cl, Br) are the strongest pure acids isolated to date [1,2] suggests that the analogous diprotic boron acids H 2 (B 12 X 12 ) may have comparable or even higher acidity. The hydrated acids [H(H 2 O) n + ] 2 [B 12 X 12 2− ] were prepared many years ago from aqueous solutions of their alkali metal salts using an ion-exchange resin in acid form [3] and were shown to be slightly stronger acids than H 2 SO 4 in aqueous solution. However, the anhydrous acids are unknown. Can they be synthesized? Are they superacids? Of further interest is that the B 12 H 12 2− ion starting material is considerably cheaper than the isoelectronic CB 11 H 12 − carborane ion, so there is potential for cost savings relative to carborane acids, which are too expensive for widespread use.An indication that the all-boron acids H 2 (B 12 X 12 ) should show comparable acid strengths to their analogous carborane acids H(CHB 11 X 11 ) comes from the position of their anions on the ν(NH) basicity scale. In this ranking, the N-H stretching frequencies of contact-ion-pair trioctylammonium salts Oct 3 N + -H⋯anion − are compared in CCl 4 solution. [2,4] The higher the ν(NH) frequency, the lower the basicity of the anion. As shown in Table 1, the B 12 Cl 12 2− salt has almost the same ν(NH) frequency as the CHB 11 Cl 11 − salt. This result is surprising inasmuch as the dinegative charge on the B 12 Cl 12 2− ion might have been expected to render it more basic than the uninegative CHB 11 Cl 11 − ion. It suggests that chloride substituents on both anions form an effective screen for negative charge that is delocalized and buried within the icosahedral cage. Similar conclusions can be drawn from the data on the B 12 Br 12 2− ion, although low solubility of its trioctylammonium salt in CCl 4 allow comparisons to be made only for crystalline salts. It is also clear from the data in Table 1 that the boron anions are much less basic than the (HSO 4 ) 2 2− ion, so their conjugate acids are expected to be much stronger than 100% H 2 SO 4 , whose acidity (H 0 =−12 on the Hammett scale) defines the onset of superacidity. ** We thank Prof. Dr. E. S. Stoyanov for invaluable assistance with the IR measurements and their interpretation and Dr. Bruno Donnadieu for X-ray crystallographic support. This work was supported by the National Science Foundation (CHE-039878 to C.A.R. and an NSF Graduate Fellowship to A.A.).

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The Strongest Isolable Acid

Cited by 37 publications

References 17 publications

A Strong Acid that Does Not Protonate Water

A Strong Acid that Does Not Protonate Water

Putting tert‐Butyl Cation in a Bottle

Superacidity of Boron Acids H₂(B₁₂X₁₂) (X=Cl, Br)

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The Strongest Isolable Acid

Cited by 37 publications

References 17 publications

A Strong Acid that Does Not Protonate Water

A Strong Acid that Does Not Protonate Water

Putting tert‐Butyl Cation in a Bottle

Superacidity of Boron Acids H2(B12X12) (X=Cl, Br)

Contact Info

Product

Resources

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Superacidity of Boron Acids H₂(B₁₂X₁₂) (X=Cl, Br)