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Brpnsted

Many solids have foreign atoms or molecular groupings on their surfaces that are so tightly held that they do not really enter into adsorption-desorption equilibrium and so can be regarded as part of the surface structure. The partial surface oxidation of carbon blacks has been mentioned as having an important influence on their adsorptive behavior (Section X-3A) depending on conditions, the oxidized surface may be acidic or basic (see Ref. 61), and the surface pattern of the carbon rings may be affected [62]. As one other example, the chemical nature of the acidic sites of silica-alumina catalysts has been a subject of much discussion. The main question has been whether the sites represented Brpnsted (proton donor) or Lewis (electron-acceptor) acids. Hall... [Pg.581]

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... [Pg.718]

Fig. XVIII-20. Spectra of pyridine adsorbed on a water-containing molybdenum oxide (IV)-Al203 catalyst L and B indicate features attributed to pyridine adsorbed on Lewis and Brpnsted acid sites, respectively. (Reprinted with permission from Ref. 191. Copyright 1976 American Chemical Society.)... Fig. XVIII-20. Spectra of pyridine adsorbed on a water-containing molybdenum oxide (IV)-Al203 catalyst L and B indicate features attributed to pyridine adsorbed on Lewis and Brpnsted acid sites, respectively. (Reprinted with permission from Ref. 191. Copyright 1976 American Chemical Society.)...
A more general theory of acids and bases was devised independently by Johannes Br0n sted (Denmark) and Thomas M Lowry (England) m 1923 In the Brpnsted-Lowry approach an acid is a proton donor, and a base is a proton acceptor The reaction that occurs between an acid and a base is proton transfer... [Pg.33]

The acid dissociation constant has the same form m Brpnsted-Lowry as m the Arrhenius approach but is expressed m the concentration of H30" rather than The concentration terms [H30" ] and [H" ] are considered equivalent quantities m equilibrium constant expressions... [Pg.35]

Even though water is a reactant (a Brpnsted base) its concentration does not appear m the expression for because it is the solvent The convention for equilibrium constant expressions is to omit concentration terms for pure solids liquids and solvents... [Pg.35]

Water can also be a Brpnsted acid donating a proton to a base Sodium amide (NaNH2) for example is a source of the strongly basic amide ion which reacts with water to give ammonia... [Pg.35]

Consider first the case of adding a strong acid such as HBr to water The equation for the Brpnsted acid-base reaction that occurs between them is... [Pg.43]

Analyzing acid-base reactions according to the Brpnsted-Lowry picture provides yet another benefit Table 1 7 which lists acids according to their strength m descending... [Pg.44]

The same G N Lewis who gave us electron dot formulas also suggested a way of think mg about acids and bases that is more general than the Brpnsted-Lowry approach Where Brpnsted and Lowry viewed acids and bases as donors and acceptors of protons (positively charged) Lewis took the opposite view and focused on electron pairs (negatively charged) According to Lewis an acid is an electron pair acceptor and a base is an electron pair donor... [Pg.45]

Clearly the two reactions are analogous and demonstrate that the reaction between hydroxide ion and hydrogen bromide is simultaneously a Brpnsted acid-base reaction and a Lewis acid Lewis base reaction Br0nsted acid-base reactions constitute a sub category of Lewis acid Lewis base reactions... [Pg.46]

This chapter sets the stage for all of the others by reminding us that the relationship between structure and properties is what chemistry is all about It begins with a review of Lewis structures moves to a discussion of the Arrhenius Brpnsted-Lowry and Lewis pictures of acids and bases and the effects of structure on acidity and basicity... [Pg.47]

Section 1 13 According to the Brpnsted-Lowry definitions an acid is a proton donor and a base is a proton acceptor... [Pg.49]

Basicity constants are not necessary in the Brpnsted-Lowry approach Basicity is measured according to the pA of the conjugate acid The weaker the conjugate acid the stronger the base... [Pg.50]

This IS a very useful relationship You should practice writing equations according to the Brpnsted-Lowry definitions of acids and bases and familiarize yourself with Table 1 7 which gives the s of various Br0n sted acids... [Pg.50]

We saw m Chapter 1 especially m Table 1 7 that alcohols resemble water m respect to their Brpnsted acidity (ability to donate a proton/rom oxygen) They also resemble water m their Brpnsted basicity (ability to accept a proton on oxygen) Just as proton transfer... [Pg.153]

The first step of this new mechanism is exactly the same as that seen earlier for the reaction of tert butyl alcohol with hydrogen chloride—formation of an alkyloxonmm ion by proton transfer from the hydrogen halide to the alcohol Like the earlier exam pie this IS a rapid reversible Brpnsted acid-base reaction... [Pg.164]

Step 3 IS new to us It is an acid-base reachon m which the carbocation acts as a Br0n sted acid transferrmg a proton to a Brpnsted base (water) This is the property of carbo cations that is of the most significance to elimination reactions Carbocations are strong acids they are the conjugate acids of alkenes and readily lose a proton to form alkenes Even weak bases such as water are sufficiently basic to abstract a proton from a carbocation... [Pg.206]

Step 3 Deprotonation of tert butyloxonium ion Water acts as a Brpnsted base... [Pg.248]

The second stage is a Brpnsted acid-base reaction and is fast... [Pg.337]

The mechanism of enolization involves two separate proton transfer steps rather than a one step process m which a proton jumps from carbon to oxygen It is relatively slow m neutral media The rate of enolization is catalyzed by acids as shown by the mechanism m Figure 18 1 In aqueous acid a hydronium ion transfers a proton to the carbonyl oxygen m step 1 and a water molecule acts as a Brpnsted base to remove a proton from the a car bon atom m step 2 The second step is slower than the first The first step involves proton transfer between oxygens and the second is a proton transfer from carbon to oxygen... [Pg.759]

Step 2 A water molecule acts as a Brpnsted base to remove a proton from the a carbon atom of the protonated aldehyde or ketone... [Pg.760]

Two molar equivalents of amine are required m the reaction with acyl chlorides and acid anhydrides one molecule of amine acts as a nucleophile the second as a Brpnsted base... [Pg.859]

Citing amine basicity according to the of the conjugate acid permits acid-base reac tions involving amines to be analyzed according to the usual Brpnsted relationships For example we see that amines are converted to ammonium ions by acids even as weak as acetic acid... [Pg.919]

Base According to the Arrhenius definition (Section 1 12) a substance that ionizes in water to produce hydroxide ions According to the Brpnsted-Lowry definition (Section 1 13) a substance that accepts a proton from some suitable donor According to the Lewis definition (Section 1 17) an electron pair donor... [Pg.1277]

Conjugate acid (Section 1 13) The species formed from a Brpnsted base after it has accepted a proton Conjugate addition (Sections 1010 and 1812) Addition reaction in which the reagent adds to the termini of the con jugated system with migration of the double bond synony mous with 1 4 addition The most common examples include conjugate addition to 1 3 dienes and to a 3 unsaturated car bonyl compounds... [Pg.1279]

Conjugate base (Section 1 13) The species formed from a Brpnsted acid after it has donated a proton... [Pg.1279]

Satisfactory Brpnsted correlations for a-substituted azoles offer further evidence of the lesser importance of steric effects in the azole series (78AHC(22)7l). [Pg.52]

As Olah et al. have reported (81JOC2706), iV-nltropyrazole in the presence of Lewis or Brpnsted acid catalysts is an effective nitrating agent for aromatic substrates. The greater lability of the N—NO2 bond in iV-nltropyrazole compared with aliphatic nltramines was discussed on the basis of its molecular structure as determined by X-ray crystallography. [Pg.270]


See other pages where Brpnsted is mentioned: [Pg.224]    [Pg.584]    [Pg.719]    [Pg.734]    [Pg.735]    [Pg.56]    [Pg.837]    [Pg.837]    [Pg.920]    [Pg.937]    [Pg.229]    [Pg.156]   
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Acid-base theory Brpnsted

Acidity Brpnsted

Acidity Brpnsted and

Acidity Brpnsted-Lowry concept

Acids Brpnsted-Lowry concept

Acids Brpnsted-Lowry definition

Acids Brpnsted-Lowry theory

Acids and Bases The Brpnsted-Lowry Definition

Acid—base reactions Brpnsted-Lowry

Alcohols as Brpnsted bases

Aldols asymmetric catalysis, Brpnsted acids

Amination reactions Brpnsted base catalysis

Bases Brpnsted-Lowry concept

Bases Brpnsted-Lowry definition

Basicity Brpnsted Lowry

Baylis-Hillman reactions Brpnsted acid catalysts

Bifunctional Brpnsted base/acid catalysis

Brpnsted Acid Catalysis Hydrogen-Bonding Activation

Brpnsted Acid Catalyzed Enantioselective Additions

Brpnsted Acid-Catalyzed Cascade Reactions

Brpnsted Acidity and Basicity

Brpnsted a-values

Brpnsted acid

Brpnsted acid activation

Brpnsted acid catalysis Mannich reactions

Brpnsted acid catalysis asymmetric aldol reaction

Brpnsted acid catalysis bases

Brpnsted acid catalysis catalysts

Brpnsted acid catalysis natural products

Brpnsted acid catalysis reactions

Brpnsted acid catalysis reductions

Brpnsted acid catalyzed enantioselective

Brpnsted acid catalyzed transfer

Brpnsted acid chiral

Brpnsted acid dissociation

Brpnsted acid reduction

Brpnsted acid sites

Brpnsted acid sites in zeolites

Brpnsted acid sites interaction

Brpnsted acid-base systems

Brpnsted acid-promoted reactions

Brpnsted acid/base

Brpnsted acidic strength

Brpnsted acidic surface

Brpnsted acidity characterization

Brpnsted acidity, catalyst activity

Brpnsted acids Lewis base-, system

Brpnsted acids addition

Brpnsted acids and bases

Brpnsted acids catalysis

Brpnsted acids dissociation constants

Brpnsted acids glycosylation

Brpnsted acids reaction

Brpnsted acids super

Brpnsted acids, proton transfer from

Brpnsted adds

Brpnsted base catalysis

Brpnsted base catalysis bifunctional catalysts

Brpnsted base catalysis compounds

Brpnsted base catalysis nucleophiles

Brpnsted base catalysis reactions

Brpnsted base chiral

Brpnsted base/acid catalysis bond formation

Brpnsted base/acid catalysis organocatalysis

Brpnsted base/acid catalysis structure

Brpnsted bases

Brpnsted basicity

Brpnsted catalysis equation

Brpnsted catalysis law

Brpnsted coefficient

Brpnsted equation

Brpnsted parameters

Brpnsted plots

Brpnsted plots biphasic

Brpnsted plots nucleophilic substitution

Brpnsted relation

Brpnsted relationship

Brpnsted relationship measurements

Brpnsted sites

Brpnsted slope

Brpnsted superacids

Brpnsted theory

Brpnsted, Johannes

Brpnsted-Evans-Polanyi

Brpnsted-Evans-Polanyi relation

Brpnsted-Evans-Polanyi relationship

Brpnsted-Lewis Superacids

Brpnsted-Lowiy bases

Brpnsted-Lowry

Brpnsted-Lowry acid, ionization

Brpnsted-Lowry acid-base

Brpnsted-Lowry acid-base definition

Brpnsted-Lowry acid-base theory

Brpnsted-Lowry acidity

Brpnsted-Lowry acids and bases

Brpnsted-Lowry acids, and

Brpnsted-Lowry bases alkenes

Brpnsted-Lowry concept

Brpnsted-Lowry model

Brpnsted-Lowry proton transfer

Brpnsted-Lowry theory of acids and

Brpnsted-Lowry theory of acids and bases

Carbonyl compounds Brpnsted base catalysis

Catalyst Brpnsted acidity

Catalysts Brpnsted acid

Chiral Brpnsted Acid-Organocatalyzed Biginelli Reactions

Conjugate additions Brpnsted base catalysts

Hydrogen ions , Brpnsted-Lowry acid

Hydrogen-bonding activation Brpnsted acids

Imines Brpnsted acid catalysis

Ketones Brpnsted acid catalysts

Kinetics Brpnsted acid-catalysis

Lewis acidity, and Brpnsted

Lewis-Brpnsted acid , asymmetric

Lewis-Brpnsted acid , asymmetric protonation

Lewis-Brpnsted mesoporous

Lowry-Brpnsted acids

Lowry-Brpnsted bases

Metal oxides with Brpnsted acids

Michael addition Brpnsted base catalysis

Michael additions Brpnsted acid

Nucleophilic reactions Brpnsted base catalysts

Prolines Brpnsted acid catalysts

Proton Brpnsted sense

Proton transfer Brpnsted-Lowry acid-base definition

Pyridine, Brpnsted acid catalysis

Strong Brpnsted acids

Superacids conjugate Brpnsted-Lewis

The Acid-Base Concept According to Brpnsted and Lowry

The Brpnsted Catalysis Law

The Brpnsted-Lowry Theory

Theories Brpnsted-Lowry

Thiourea Brpnsted acid catalysts

Water Brpnsted-Lowry theory

Water as a Brpnsted base

Zeolite catalysis Brpnsted acid sites

Zeolites Brpnsted acid sites

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