Carbon acidity. 97. Cesium ion pair acidity of some sulfones in cyclohexylamine

The ion pair acidities of several sulfones were measured on the cesium-cyclohexylamine scale. Cyclopropyl phenyl sulfone is less acidic than isopropyl phenyl sulfone in agreement with earlier results in dimethyl sulfoxide. The acidities of a series of substituted phenyl methyl sulfones show that the sulfone group is an effective insulator; there is no significant delocalization of carbanion charge across the sulfone group into the phenyl ring. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 533–537, 1997     

Hydrogen-bonding. Part 5. A thermodynamically-based scale of solutehydrogen-bond acidity

A scale of solute hydrogen-bond acidity has been constructed for over 150 solutes, based on logK values for the hydrogen-bond complexation of solutes with reference bases in CCl₄ There is no general connection between quantities characteristic of full proton transfer, and our hydrogen-bond acidity scale, so that the latter represents a new solute acidity parameter.     

Bilirubin acidity. Titrimetric and 13C NMR studies.

Acidimetric titration of bilirubin IX-alpha, dissolved in excess aqueous sodium hydroxide, showed that two protons are dissociated with pK values well below 7 and that one or several additional acidic groups titrate with pK around 12.9. Precipitation of the nearly insoluble acid precluded determination of the two lower pK values by titration in aqueous solution. In dimethyl sulfoxide solution, four acidic protons were demonstrated, titrating two by two without precipitation. 13C NMR spectra of bilirubin IX-alpha were recorded and complete assignments were made by comparison with the spectra of bilirubin XIII-alpha and mesobilirubin etc. Such spectra, recorded after addition of 2 and 4 mol of base per mol of bilirubin IX-alpha, showed that both carboxyl groups are titrated by the first 2 mol of base, and both lactams by the following 2 mol of base. Cotitrations of bilirubin IX-alpha with other acids, o- and m-hydroxybenzoic acid and 2-pyridone, were used to determine relative pK values in dimethyl sulfoxide solution, and pK values for the four acidic protons of bilirubin IX-alpha in aqueous solution were calculated from the Born equation. Both carboxyl groups exhibited pK = 4.4, and both lactams pK = 13.0, in good agreement with values expected from the chemical structure of the bilirubin molecule. The implications of these findings for understanding the mechanism of bilirubin neurotoxicity are discussed.     

Bulk gas-phase acidity

The capability of a gaseous Br?nsted acid HB to deliver protons to a base is usually described by the gas-phase acidity (GA) value of the acid. However, GA values are standard Gibbs energy differences and refer to individual gas pressures of 1?bar for acid HB, base B(-), and proton H(+). We show that the GA value is not suited to describe the bulk acidity of a gaseous acid. Here the pressure dependence of the activities of HB, H(HB)(n)(+), and B(HB)(m)(-) that result from gaseous autoprotolysis have to be considered. In this work, the pressure-dependent absolute chemical potential of the proton in the representative gaseous proton acids CH(4), NH(3), H(2)O, HF, and HCl was worked out and the general theory to describe bulk gas phase acidity--that can directly be compared with solution acidity--was developed.     

Gas-phase acidity of D-glucose. A density functional theory study

The gas-phase acidity of D-glucopyranose was studied by means of B3LYP calculations combined with 6-31G(d,p) or 6-31+G(d,p) standard basis sets. For each anomer, deprotonation of the various primary and secondary hydroxyl groups was considered. As in solution, the anomeric hydroxyl is found to be the most acidic for both anomers, but only when the 6-31+G(d,p) basis set is used for geometry optimization. Deprotonation of the anomeric hydroxyl induces an important C(1)--O endocyclic bond elongation and subsequently promotes an energetically favored ring-opening process as attested by the very small calculated activation barriers. The results also suggest that interconversion between the various deprotonated alpha- and beta-anomers may easily occur under slightly energetic conditions. B3LYP/6-311+G(2df,2p) calculations led to the an absolute gas-phase acidity of deltaacidGo(298)(alpha-D-glucose) = 1398 kJ mol(-1). This estimate matches well the only experimental value available to date. Finally, this study again confirms that the use of diffuse functions on heavy atoms is necessary to describe anionic systems properly and to achieve good relative and absolute gas-phase acidities.     

Semiautomatic flow-injection method for determination of volatile acidity in wines.

A flow-injection (FI) method based on analytical pervaporation was assessed for its routine use in the determination of volatile acidity in winery laboratories. The new method was compared with both the official method and the Mathieu method, which is most often used in Spanish wineries, by testing 30 different wines, including young and aged, and sweet and dry wines from Montilla-Moriles appellation d'origine. The robustness of the new method was established, and then all 3 methods were studied in terms of range of linearity and regression of the calibration curve, repeatability, reproducibility, sensitivity, detection and quantitation limits (LOD and LOQ, respectively), and time of analysis. The FI method surpassed the Mathieu method in reproducibility and both the Mathieu and official methods in LOD and LOQ and sensitivity; it also required less personnel involvement and shorter analysis time. The statistical criteria established by the Office International de la Vigne et du Vin were applied to the data and the results obtained indicated that the differences between the analytical parameters of the 3 methods are not significant and can be applied indistinctly. The correlation of the methods was studied by taking them 2 by 2, and the corresponding equations, coefficients, and deviations confirmed the statistical results. Thus, the new method can be used in winery laboratories with clear advantages over its 2 counterparts (the routine and official methods).     

Solid aluminiumalkyl-based isomerization catalysts. Surface acidity and catalytic activity

Isomerization catalysts with high activity and selectivity were prepared by chemical anchoring of aluminiumethyldichloride on the surface of inorganic oxides. Surface acidity was studied by calorimetric and IR spectroscopy methods, and was found to correspond well with catalytic activity for m-xylene isomerization.

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Lewis acidity of gallium-containing pentasils

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2873–2874, December, 1990.     

Lewis acidity of gallium halides

The Lewis acidity of GaF(3), GaF(2)Cl, GaFCl(2), and GaCl(3) in acid-base interactions has been studied by taking ammonia as their electron-donating counterpart. We have derived an unoccupied reactive orbital that shows the maximum localization on the Ga atomic center for each species. The orbital is located lower in energy compared to those in the corresponding boron and aluminum halides. In contrast to boron halides, the unoccupied reactive orbital of the acid site tends to be delocalized considerably on the halogens as the fluorines are substituted by chlorines in gallium halides. The trend observed in the effects of fluorine and chlorine on the acidity of the gallium halides is opposite to those found in the boron halides. This cannot be interpreted solely in terms of the electron-accepting strength of the gallium center, but can be understood by including electrostatic interactions and closed-shell repulsion with ammonia in the adducts. The origin of the difference in Lewis acidity of BCl(3), AlCl(3), and GaCl(3) has been clarified.     

Amperometric monitoring of bacteria-induced milk acidity using a platinum disc microelectrode.

The acidity induced by the action of bacteria in milk samples was monitored amperometrically by using a platinum microelectrode. The measurements were performed directly on commercial packs of milk, stored at 32 degrees C, and were continued for 9-10 d after inoculation. The data were compared with those obtained by measuring the pH of the samples and the results are discussed on the basis of the metabolism of each bacterial species. The effects of the following bacteria were examined: Staphylococcus aureus, Bacillus cereus, Streptococcus faecalis, Bacillus subtilis, Aeromonas, and Corynebacterium.     

The acidity of fluorinated bicycloalkanes. 1. 1 -Undecafluoro- and 1 ,4 -decafluorobicycloheptanes

CNDO/2 Calculations have been performed on the title compounds and on the anions derived from them. The results indicate that in the anion there is significant transannular transfer of charge to the 4-position. The amount of such transfer is effectively independent of the 4-substituent. It is concluded that the effect of the substituent upon the stability of the acid must be an important factor.     

Surface acidity of cerium exchanged Y-zeolite

Surface acidities of Ce^III, Ce^IV and [Ce^III, Ce^IV] containing Na-Y zeolites were determined by means of n-butylamine titration in benzene using Hammett indicators in the range H_o: +6.8 to H_o: –8.2. Total acidites of Ce^IVNaY zeolites until 51% Ce^IV exchange were found to be small (0.80 mequ/g at H_o: +6.8) but formed preferably strong acidic centers (H_o: –5.6) even at low degrees of exchange. Ce^IIINaY displayed an acidity pattern similar to that which is known from lanthanum exchanged NaY faujasites under the same pretreatment conditions.

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NaY, Ce^III, Ce^IV [Ce^III, Ce^IV], -, H_o: +6,8 H_o:–8,2. Ce^IVNaY 51%- Ce^IV (=0,80 / H_o: +6,8), (H_o: –5,6) . Ce^IIINaY NaY .

     

TPD study of catalyst surface acidity

Acidity of catalyst surfaces of different nature such as -Al₂O₃, natural zeolite-clinoptilolite, and synthetic zeolite zeokar by adsorption of ammonia over a wide temperature range has been studied. Ammonia is adsorbed on the catalysts with different strengths, as evidenced by the presence of different types of acid sites.

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(-Al₂O₃, - , () . , , .

     

Factors influencing the acidity of nitro-compounds

Conclusions The factors influencing the acidity of aliphatic nitro-compounds were discussed, and an attempt was made to estimate quantitatively the contributions of the inductive and mesomeric effects to the values of the ionization constants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1048–1054, March, 1968.     

Surface acidity of supported vanadia catalysts

The surface acidity of SiO₂, γ-Al₂O₃ and TiO₂ supported vanadia catalysts has been studied by the microcalorimetry and infrared spectroscopy using ammonia as the probe molecule. The acidity in terms of nature, number and strength was correlated with surface structures of vanadia species in the catalysts, characterized by X-ray diffraction and UV-Vis spectroscopy. It was found that the dispersion and surface structure of vanadia species depend on the nature of supports and loading and affect strongly the surface acidity. On SiO₂, vanadium species is usually in the form of polycrystalline V₂O₅ even for the catalyst with low loading (3%) and these V₂O₅ crystallites exhibit similar amount of Brönsted and Lewis acid sites. The 25%V₂O₅/SiO₂ catalyst possesses substantial amount of V₂O₅ crystallites on the surface with the initial heat of 105 kJ mol^-1 and coverage of about 600 mmol g^-1 for ammonia adsorption. Vanadia can be well dispersed on g-Al₂O₃and TiO₂ to form isolated tetrahedral species and polymeric two-dimensional network. Addition of vanadia on γ-Al₂O₃ results in the change of acidity from that associated with g-Al₂O₃ (mainly Lewis sites) to that associated with vanadia (mainly Brönsted sites) and leads to the decreased acid strength. The 3%V₂O₅/TiO₂ catalyst may have the vanadia structure of incomplete polymeric two-dimensional network that possesses the Ti-O-V-OH groups at edges showing strong Brönsted acidity with the initial heat of about 140 kJ mol^-1 for ammonia adsorption. On the other hand, the 10%V₂O₅/TiO₂ catalyst may have well defined polymeric two-dimensional vanadia network, possessing V-O-V-OH groups that exhibit rather weak Brönsted acidity with the heat of 90 kJ mol^-1 for NH₃ adsorption. V₂O₅ crystallites are formed on the 25%V₂O₅/TiO₂ catalyst, which exhibit the acid properties similar to those for 25%V₂O₅ on SiO₂ and γ-Al₂O₃.