Br0nsted acids compounds

The tendency for a Br0nsted acid to act as a proton donor, expressed in terms of the compound s dissociation constant in water. 2. The term also refers to the tendency to form a Lewis adduct, as measured by a dissociation constant. 

Rare-earth exchanged [Ce ", La ", Sm"" and RE (RE = La/Ce/Pr/Nd)] Na-Y zeolites, K-10 montmorillonite clay and amorphous silica-alumina have also been employed as solid acid catalysts for the vapour-phase Beckmann rearrangement of salicylaldoxime 245 to benzoxazole 248 (equation 74) and of cinnamaldoxime to isoquinoline . Under appropriate reaction conditions on zeolites, salicyl aldoxime 245 undergoes E-Z isomerization followed by Beckmann rearrangement and leads to the formation of benzoxazole 248 as the major product. Fragmentation product 247 and primary amide 246 are formed as minor compounds. When catalysts with both Br0nsted and Lewis acidity were used, a correlation between the amount of Br0nsted acid sites and benzoxazole 248 yields was observed. 

The hydrogen-bond complex 5 and ion pair 6 are activated form of the carbonyl compounds. The nucleophilic addihon of carbon nucleophile to carbonyl compounds and imines may be accelerated by acid catalysis. Nucleophilic attack to carbonyl compounds or imine took place either by way of 5 or 6 to furnish addihon product. If HX activates carbonyl compound by forming hydrogen-bond complex 5 and nucleophilic addition takes place to give an adduct, the reaction is a hydro-gen-bond catalyzed reaction (Scheme 2.5). In contrast, when ion pair 6 is formed and nucleophilic addihon occurs, the reachon is a Br0nsted-acid-catalyzed reachon. 

The observed effects of structure on rate and on orientation, confirmed by the Brown selectivity relationship, show that there is no basic difference between heterogeneous catalytic alkylation of aromatic compounds and homogeneous electrophilic aromatic substitution, cf. nitration, sul-phonation etc. This agreement allows the formulation of the alkylation mechanism as an electrophilic attack by carbonium ion-like species formed on the surface from the alkene on Br0nsted acidic sites. The state of the aromatic compound attacked is not clear it may react directly from the gas phase (Rideal mechanism ) [348] or be adsorbed weakly on the surface [359]. 

There have been a number of reports of improved selectivity with sulfonic acid resin catalysts compared with conventional liquid acid catalysts[6—9]. Various explanations have also been proposed. If mechanisms usually postulated for condensation reactions with liquid Br0nsted acid [10] and solid acid catalysts [11] are adopted, the sequence of steps shown in Fig. 2 could be considered for the condensation of MFC. Both mechanisms incorporate the essential features of known carbenium ion chemistry, i.t., electrophilic attack on the aromatic ring by polar carbenium ion intermediates. Note that MDU is formed by this attack on the benzene ring of MPC, while the N—benzyl compound by the attack on nitrogen atom. 

Bromoethynes, in iron cluster compounds, 6, 296 4-Bromothiazoles, synthesis, 9, 38-39 Br0nsted acids, in fluoride abstraction, 1, 735 Buckyferrocenes, synthesis, 6, 187 Butadienes... 

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 most important. S, .S -acetals in organic chemistry are the six-membered ring S,S-acetals, the so-called dithianes (formulas A, C, and F in Figure 7.22). Dithianes are produced from carbonyl compounds and 1,3-propanedithiol usually in the presence of Lewis instead of Br0nsted acids. 

Despite their normalization to/oc, A)qc values for individual pesticide compounds stiU vary among different soils and sediments, though to a much lesser extent than Kp values (Curtis et al, 1986). These variations in Koc, which typically span a factor of 10 or less for individual pesticide compounds (e.g., Mackay et al., 1997), are presumed to arise from variations in the sorption properties of the biogenic materials of which NOM is comprised (Shin et al, 1970), changes in the chemical properties of NOM caused by weathering (Chiou, 1998) or, for ionic compounds or Br0nsted acids, variations in solution properties such as pH and salinity (Schwarzenbach et al, 1993). 

One of the fundamental properties of compounds containing hydrogen is their ability to act as proton donors, that is, as Br0nsted acids. 

Among organic compounds, we can expect appreciable Lowry-Br0nsted acidity from those containing O—H, N—H, and S-H groups. 

Protonated aliphatic/alicyclic nitro compounds have not been studied to the same extent as the nitroarenes. However, the isomeric [C2H6N02]+ ions and their rearrangement in the gas phase have been subject to studies . The protonated ethyl nitrite and nitroethane were generated by proton transfer from different Br0nsted acids. In addition, protonated ethyl nitrite was obtained as a result of addition of NO+ to ethanol. The existence of two different [C2H6N02]" structures, i.e. protonated ethyl nitrite and protonated nitroethane, was demonstrated. Slow isomerization of protonated nitroethane to protonated ethyl nitrite has been elucidated see Scheme 40. 

Clays catalyze numerous carbon-carbon bond-forming reactions as solid acids [8-10]. Montmorilonites of smectite hydrophilic clays are composed of negatively charged two-dimensional layers and an interlayer with cationic species, which can be easily exchanged for other cations. It is well known that proton forms of montmorillonite (H+-mont) acted as a Br0nsted acid catalyst [1, 2], which mediates addition reactions of 1,3-dicarbonyl compounds to alkenes and alcohols (Scheme 6.6) (93). 

However, perchloric acid and other Br0nsted acids do not conduct electricity in oxygen-free solvents. Thus, they are covalent compounds under these conditions. Cationically polymerizable monomers are, however, Br nsted bases, so Equation (18-79) must be replaced by... 

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