Strong Superacids Research Articles

On the Protonation and Deuteration of Simple Phenols**

AbstractIn analogy with the reaction of phenols with very strong super acids, these compounds can be protonated by the weaker super acid trifluoroacetic acid (TFA) and trifluoromethanesulphonic acid (TFS) also giving rise to the formation of OH and/or ring protonated products, which can be identified unambiguously by means of 1HNMR spectroscopy. The same reactions are possible with the deuterated acids TFA‐d and TFS‐d. However, from these reactions, additional information on the proton and deuterium attack at different positions in the phenolic compounds is possible not detectable by the hitherto used non‐deuterated acids. Moreover, the reaction of phenols with these deuterated acids allows the preparation of partially or fully deuterated phenols that are also important as markers in biological application and material chemistry.

Exploration of Superacidic Properties of HMnFn (n = 1–6) Using Density Functional Theory

AbstractSuperacids play a key role as catalysts in various processes, such as acylation, esterification, and protonation of diverse chemical compounds. In the present investigation, HMnFn (n = 1–6) superacid series are studied within the quantum chemical framework using density functional theory with the B3LYP functional. The new superacid series is created through protonation of MnFn superhalogen complexes. Various molecular geometries, for example, HMnF, HMnF2, HMnF3, HMnF4, HMnF5, and HMnF6, are optimized to their respective global energy minimum and molecular properties are analyzed. First, the normal mode frequencies are analyzed in order to verify that the geometries are associated with their respective global minimum. Second, the Gibbs free energy of deprotonation ΔGacid is computed to estimate acidity of the molecules in gas phase. A compound is classified as a superacid if ΔGacid value is below 300 kcal mol−1. The HMnFn superacid series is found to have ΔGacid values well below this threshold of 300 kcal mol−1 and strength is comparable with fluoroantimonic acid (HSbF6), which is the strongest superacid known having ΔGacid value of 255.5 kcal mol−1.

The Combination of Superhalogens and Brønsted Acids HX (X = F, Cl, Br): An Effective Strategy for Designing Strong Superacids.

A series of 27 composite structures, consisting of superhalogen and Brønsted acid, is designed and systematically studied based on combined ab initio and DFT calculations focusing on their potentials as novel superacids. As indicated by high-level CCSD(T) results, all the composites here fulfill the theoretical criterion for superacid and the acidities of two of them are close to the strongest superacid ever reported. The influences of various factors on the superacid properties of these composites were analyzed in detail. Our results demonstrate that the acidity of these superacids is mainly determined by the superhalogen components while the effect of Brønsted acids, irrespective of their number or type, is relatively mild. Therefore, it is probable to design novel composite superacid with enhanced property through the regulation of the superhalogen component. It is encouraging that MP2 and DFT could also provide reliable results when compared with the high-level CCSD(T) method. The reliability of these low-cost methods implies the capability of theoretical calculations for future composite superacid of enlarged size, and thus it is highly probable that an effective guide to the related experimental research could be provided by the theory.

Protonation of ninhydrin and indan-1,2,3-trione revisited: A combined theoretical and experimental study

The literature data on protonation of indan-1,2,3-trione and ninhydrin (indantrione hydrate) in acidic media are inconsistent, formation of dications at pH 3 and very low extent of protonation in superacid CF3SO3H were claimed. Our combined theoretical (DFT, MP2, CCSD) and experimental (NMR) study has shown that indantrione undergoes single protonation in CF3SO3H resulting in monocation formation. In more strong superacid FSO3H-SbF5 dication is formed, but, contrary to the literary data, trication is not formed even in this superacid. Significant dependence of 13C NMR chemical shifts of indantrione on media acidity allows using this compound as a convenient indicator of acidity in a broad range, from H0 −3 to −25.

The existence and gas phase acidity of the HAlnF3n+1 superacids (n = 1–4)

Novel strong superacids are proposed and investigated on the basis of ab initio calculations. The gas phase acidity of the HAlF4, HAl2F7, and HAl3F10 systems evaluated by the estimation of the Gibbs free energies of their deprotonation reactions were found significant and comparable to the corresponding value characterizing the HTaF6, whereas the strength of the HAl4F13 acid was predicted to exceed that of the HSbF6 acid (the strongest liquid superacid recognized). The deprotonation energies of the HAlnF3n+1 acids (n=1–4) turned out to be closely related to the electronic stabilities of their corresponding (AlnF3n+1)− anions.

Acid strength of solids probed by catalytic isobutane conversion

The literature is controversial on whether sulfated zirconia (SZ) is “just” as strong acid as H-zeolites, or a strong superacid. Spectroscopic studies of adsorbed probe molecules concluded that SZ is not a superacid, whereas acidity measurements based on Hammett indicators, alkane transformations and the 1/2% isobutane conversion test [B. Umansky, J. Engelhardt, W.K. Hall, J. Catal. 127 (1991) 128; D. Fraenkel, Chem. Lett. (1999) 917] indicated that SZ is superacidic. We for the first time applied direct acidity measurements under comparative conditions for SZ and common H-zeolites in a single series and found that the apparent acid strength order is SZ ( H 0 ∼ −18) ≫ HM (−14) > HZSM-5 (−10) ≈ HY (−9), in agreement with previous studies employing the zeolites and SZ separately. Product distribution at 1/2% isobutane conversion is in full agreement with the acid ranking and strength; SZ gives the typical pattern of known superacids (Magic Acid®, HCl–AlCl 3), whereas the weaker acid zeolites’ pattern is consistent with that of other weaker acids.

Reaction mechanisms on liquid and solid acid catalysts. Correlation with acidity

The probe bases used for measurement of strength of acid catalysts need to be structurally similar to the catalytic substrates. Traditional acidity measurements are inapplicable when the hydron transfer forms a tight ion pair, as on solid acids. Also, solid acids are much weaker than liquid acids of similar structure. Alkane activation by C–H and C–C cleavage, evidenced in strong superacids, does not occur in less strongly acidic media. The reactivity patterns and structure–reactivity relationships are the same for the cationoidic species (weakly coordinated carbocations) occurring in the less strong acids as for the full-fledged carbocations intervening in superacids. Even in trifluoromethanesulfonic acid, a weak superacid, the first step in alkane activation is an oxidation, forming unsaturated carbocations. On sulfated zirconia, the first step of alkane reactions is a one-electron oxidation. Mechanistic features incompatible with standard (or “traditional”) carbocationic processes, are observed in the reaction of 3-methylpentane on the zeolite HZSM-5.

Mechanisms of n-butane isomerization over superacidic sulfated metal oxides

Superacidic sulfated metal oxides were prepared by impregnating different metal oxides (or hydroxides) with sulfuric acids. The superacidic strength of prepared samples were compared by temperature-programmed desorption of ammonia (NH 3-TPD) and showed a trend of HS/ZrO 2>HS/MgAl 2O 4>HS/Al 2O 3>HS/Fe 2O 3. Catalytic properties of these superacidic samples towards isomerization of n-butane to isobutane were subsequently pursued. Both the activity and the isobutane selectivity increased with the superacidic strength of catalysts. Observed variation in the selectivity was interpreted with a difference in the reaction mechanism: A high selectivity was obtained from strong superacid sites that catalyze the isomerization through a revised monomolecular mechanism; while a low selectivity became dominated on weak superacid sites that favored a bimolecular mechanism. The relative importance of these two mechanisms was kinetically controlled by formation of different butyl carbenium ions (primary or secondary) while the n-butane reactant adsorbed on superacidic sites.

ChemInform Abstract: Acidity Measurements from Protonation of Aromatics. Protonation of Hexamethylbenzene by Trifluoromethanesulfonic Acid and Its Use to Relate Acidities of Strong Superacids to Acidities of Acids Included in the Traditional Hammett Scale.

ChemInformVolume 20, Issue 49 Article ChemInform Abstract: Acidity Measurements from Protonation of Aromatics. Protonation of Hexamethylbenzene by Trifluoromethanesulfonic Acid and Its Use to Relate Acidities of Strong Superacids to Acidities of Acids Included in the Traditional Hammett Scale. D. FARCASIU, D. FARCASIU Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this authorG. MARINO, G. MARINO Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this authorG. MILLER, G. MILLER Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this authorR. V. KASTRUP, R. V. KASTRUP Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this author D. FARCASIU, D. FARCASIU Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this authorG. MARINO, G. MARINO Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this authorG. MILLER, G. MILLER Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this authorR. V. KASTRUP, R. V. KASTRUP Dep. Chem., Clarkson Univ., Potsdam, NY 13699, USASearch for more papers by this author First published: December 5, 1989 https://doi.org/10.1002/chin.198949047AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue49December 5, 1989 RelatedInformation

Acidity measurements from protonation of aromatics. Protonation of hexamethylbenzene by trifluoromethanesulfonic acid and its use to relate acidities of strong superacids to acidities of acids included in the traditional Hammett scale

HBr-AlBr 3 et HF-SBF 5 sont les systemes superacides les plus forts. Estimation de l'aptitude a protoner du systeme HF-TaF 5