Br0nsted acidity molecular acids

The ability of the Si=P bond to serve as a dienophile for a [2+4]-cycloaddition (hetero-Diels-Alder reaction) has been verified by the reaction of 15a with cyclopentadiene (Eq. 10).14 The components react at 60°C in benzene to give a quantitative yield of 25, which was isolated as a colorless solid. Interestingly, a Br0nsted acid (C—H)/base (Si=P) reaction, as in the case of 15a and phenylacetylene, was not observed. In the mass spectrum of25, the molecular peak but also the free phosphasilene 15a+ have been detected. Similar behavior was observed for related ad-... 

Addition of Br0nsted acids to double bonds involving a metal center is well known in molecular chemistry [15]. Therefore, it was expected to take place when complexes bearing an alkylidene or an imido ligand were allowed to react with acidic... 

HYDRONIUM IONS (H30+), BR0NSTED ACIDS (HA), AND MOLECULAR HYDROGEN (H2)... 

HYDRONIUM IONS, BR0NSTED ACIDS, AND MOLECULAR HYDROGEN... 

The goal of this volume is to provide (1) an introduction to the basic principles of electrochemistry (Chapter 1), potentiometry (Chapter 2), voltammetry (Chapter 3), and electrochemical titrations (Chapter 4) (2) a practical, up-to-date summary of indicator electrodes (Chapter 5), electrochemical cells and instrumentation (Chapter 6), and solvents and electrolytes (Chapter 7) and (3) illustrative examples of molecular characterization (via electrochemical measurements) of hydronium ion, Br0nsted acids, and H2 (Chapter 8) dioxygen species (02, OJ/HOO-, HOOH) and H20/H0 (Chapter 9) metals, metal compounds, and metal complexes (Chapter 10) nonmetals (Chapter 11) carbon compounds (Chapter 12) and organometallic compounds and metallopor-phyrins (Chapter 13). The later chapters contain specific characterizations of representative molecules within a class, which we hope will reduce the barriers of unfamiliarity and encourage the reader to make use of electrochemistry for related chemical systems. 

The ready access of the hydroxides 1-11 opened the possibility for designing the synthesis of heterometallic complexes with the potential to be used as molecular catalysts. The synthetic strategy takes advantage of the Br0nsted acidic character of the M(0—H) moiety in building up a new class of heterometallic complexes. The aluminum hydroxide (5a-5h) can build up new heterobimetallic complexes by reacting with other suitable... 

It has already been mentioned that zeolites are shape selective with respect to molecular adsorption. This property relates to their micropores stmcture. The zeolite framework shows a limited flexibility, which is essential. For instance, Yashonath et al. have shown in their classical dynamic simulations study of molecular diffusion within zeolite micropore that the zeolite framework flexibility affects significantly diffusion when the molecules have a size comparable with the micropore size. To get an idea of the order of magnitude of this flexibility, one can consider the hybrid semi-empirical DFT periodic study of chabazite zeolite of Ugliengo et al. V They introduced in the unit cell of chabazite Br0nsted acidic sites which are known to induce an increase of the volume of around 10 This increase of the volume relates with the difference of volume between a Si04 tetraheron and a... 

The uptake of hydrogen cyanide into protonic forms of synthetic zeolites Y, Beta, mordenite, as well as into naturally occurring clinoptilolite, ferrierite, stil-bite and aliunina-pillared clays were studied by Jamis et al. [954] using FTIR measurements of the C=N stretching vibration to characterize the binding of HCN to the various Br0nsted-acid sites of the molecular sieve materials. 

Although homonuclear molecules such as CI2 and F2 are non-polar, NaQ and KCl are highly polar. It emphasised the similarity between many Br0nsted acids, with elimination of molecular compounds and a distinction between primary and secondary affinities. 

The most widely used catalysts for acid-catalyzed aldol condensations are the molecular sieve zeolites, for example, crystalline aluminosilicates of group I and II elements, in which the latter have been replaced by protons. The surface protons confer Br0nsted acidity. Among the acidic zeolites we can mention HZSM-5 (pentasil zeolite), HY (faujasite), or HM (mordenite). Recently, polystyrene-supported sulfonic acids such as those of the macroreticular strongly acidic cation-exchange resins (59) and acid-base functionalized mesoporous materials such as amine and sulfonic acid-containing SBA-15 (60) have been shown to promote the acid-catalyzed aldol condensation of aldehydes with ketones at low temperatures. 

In Fig. 18.19 the spectra relative to the adsorption of NO2 over an ammonia-covered V205-W03/Ti02 commercial catalyst are reported. Ammonia adsorption (Fig. 18.19a) occurs in two modes, as ammonium ions on Br0nsted acidic sites (broad bands at 3,020,2,800 cm NH4 stretchings, peaks at 1,668 and 1,444 cm NH4 asymmetric deformations), and in the coordinated molecular form over Lewis sites (NH3 stretchings at 3,395, 3,320, 3,250 and 3,168cm , NH3 deformation at 1,608 cm ). After contact with NO2 gas, the spectrum is significantly modified (Fig. 18.19b) this is evident as the sharp peaks at 3,400-3,200 cm disappear. 

Eder F, Lercher JA (1997) Alkane, sorption in molecular sieves the contribution of ordering, intermolecular interactions, and sorption on Br0nsted acid sites. Zeolites 18(1) 75-81... 

In Fig. 1.21a, the differential heats of adsorption of CO on H—BEA zeolite and on MFI-Silicalite are reported as a function of the adsorbed amounts. Volumetric isotherms are illustrated in the figure inset. In both cases the adsorption was fully reversible upon evacuation of the CO pressure, as typical of both physical and weak, associative chemical adsorption. For H-BEA a constant heat plateau at 60kJ mol was measured. This value is typical of a specific interaction of CO with coordinative unsaturated Al(III) atoms, as it was confirmed by combining adsorption microcalorimetry and molecular modeling [73, 74, 78, 89] Note that the heat value was close to the heat of adsorption of CO at cus Al(III) sites on transition catalytic alumina, a typical Lewis acidic oxide [55, 73], Once saturated the Al(III) defects, the heat of adsorption started decreasing down to values typical of the H-bonding interaction of CO with the Br0nsted acidic sites (- 30 kJ mol , as reported by Savitz et al. [93]) and with polar defects, either confined in the zeolite nanopores or at the external surface. 

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