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Lewis acid—bases

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]

Thirdly, the intramolecular assodation of a solvent affects the Lewis acid - base equilibrium Upon... [Pg.30]

The XeF+ cation forms Lewis acid—base adduct cations containing N—Xe—F linkages with nitrogen bases that are resistant to oxidation by the strongly oxidizing XeF+ cation having an estimated electron affinity of the XeF+ cation of 10.9 eV (12). The thermally unstable colorless salt,... [Pg.24]

Tetracyanoethylene is colorless but forms intensely colored complexes with olefins or aromatic hydrocarbons, eg, benzene solutions are yellow, xylene solutions are orange, and mesitylene solutions are red. The colors arise from complexes of a Lewis acid—base type, with partial transfer of a TT-electron from the aromatic hydrocarbon to TCNE (8). TCNE is conveniendy prepared in the laboratory from malononitrile [109-77-3] (1) by debromination of dibromoma1 ononitrile [1855-23-0] (2) with copper powder (9). The debromination can also be done by pyrolysis at ca 500°C (10). [Pg.403]

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. [Pg.2002]

R. G. Pearson, J. Am. Chem. Soc. 85 3533 (1963) T. L. Ho, Hard and Soft Acids and Bases in Organic Chemistry, Academic Press, New York, 1977 W. B. Jensen, The Lewis Acid-Base Concept, Wiley-Interscience, New York, 1980, Chapter 8. [Pg.21]

Neutral compounds such as boron trifluoride and aluminum chloride form Lewis acid-base complexes by accepting an electron pair from the donor molecule. The same functional groups that act as lone-pair donors to metal cations can form complexes with boron trifluoride, aluminum chloride, and related compounds. [Pg.234]

The chemistry of Lewis acid-base adducts (electron-pair donor-acceptor complexes) has stimulated the development of measures of the Lewis basicity of solvents. Jensen and Persson have reviewed these. Gutmann defined the donor number (DN) as the negative of the enthalpy change (in kcal moL ) for the interaction of an electron-pair donor with SbCls in a dilute solution in dichloroethane. DN has been widely used to correlate complexing data, but side reactions can lead to inaccurate DN values for some solvents. Maria and Gal measured the enthalpy change of this reaction... [Pg.425]

Drago and co-workers have correlated a large body of enthalpies of adduct formation in Lewis acid-base systems, including some solvents as reactants, with this four-parameter equation ... [Pg.426]

It is clear that some boranes are amphoteric Lewis acid/bases — that is they can act either as electron-pair donors as above or as electron-pair acceptors (e.g. in L.BH3 and L.B1H7). It follows that a borane donor could conceivably ligate... [Pg.164]

SF4 is unusual in apparently acting both as an electron-pair acceptor and an electron-pair donor (amphoteric Lewis acid-base). Thus pyridine forms a stable 1 1 adduct C5H5NSF4 which presumably has a pseudooctahedral (square-pyramidal) geometry. Likewise CsF (at 125°) and Me4NF (at —20°) form CsSFs and [NMe4]+[SFs] (Fig. 15.21a). By contrast, SF4 behaves as a donor to form 1 1 adducts with many Lewis acids the stability decreases in the sequence SbFs > AsFs > IrFs > BF3 > PF5 > ASF3. In view of the discussion on... [Pg.686]

Complex [(CXI )Ir(/j,-pz)(/i,-SBu )(/j,-Ph2PCH2PPh2)Ir(CO)] reacts with iodine to form 202 (X = I) as the typical iridium(II)-iridium(II) symmetrical species [90ICA(178)179]. The terminal iodide ligands can be readily displaced in reactions with silversalts. Thus, 202 (X = I), upon reaction with silver nitrate, produces 202 (X = ONO2). Complex [(OC)Ir(/i,-pz )(/z-SBu )(/i-Ph2PCH2PPh2)Ir(CO)] reacts with mercury dichloride to form 203, traditionally interpreted as the product of oxidative addition to one iridium atom and simultaneous Lewis acid-base interaction with the other. The rhodium /i-pyrazolato derivative is prepared in a similar way. Unexpectedly, the iridium /z-pyrazolato analog in similar conditions produces mercury(I) chloride and forms the dinuclear complex 204. [Pg.208]

Compositions of Lewis acid-based ionic liquids are generally referred to by the mole frac-... [Pg.12]

Ionic liquids derived from Lewis acids based on Ti, Nb, Sn, Sb [NR3R ]X/SbE5 Atofma, France 2001 25... [Pg.31]

Moreover, these experiments reveal some unique properties of the chlorostan-nate ionic liquids. In contrast to other known ionic liquids, the chlorostannate system combine a certain Lewis acidity with high compatibility to functional groups. The first resulted, in the hydroformylation of 1-octene, in the activation of (PPli3)2PtCl2 by a Lewis acid-base reaction with the acidic ionic liquid medium. The high compatibility to functional groups was demonstrated by the catalytic reaction in the presence of CO and hydroformylation products. [Pg.235]

Borane is very reactive because the boron atom has only six electrons in its valence shell. In tetrahydrofuran solution, BH3 accepts an electron pair from a solvent molecule in a Lewis acid-base reaction to complete its octet and form a stable BH3-THF complex. [Pg.223]

Reduction Conversion of Nitriles into Amines Reduction of a nitrile with LiAIH4 gives a primary amine, RNH . The reaction occurs by nucleophilic addition of hydride ion to the polar C=N bond, yielding an imine anion, which still contains a C=N bond and therefore undergoes a second nucleophilic addition of hydride to give a dianion. Both monoanion and dianion intermediates are undoubtedly stabilized by Lewis acid-base complexafion to an aluminum species, facilitating the second addition that would otherwise be difficult Protonation of the dianion by addition of water in a subsequent step gives the amine. [Pg.769]

The Lewis acid-base model is the most general of the three we have considered. [Pg.410]

When a complex ion is formed from a simple cation, the electron pairs required for bond formation come solely from the ligands. Reactions such as these, in which one species donates an electron pair to another, are referred to as Lewis acid-base reactions. In particular—... [Pg.410]

More recently considered candidates are large molecular anions with delocalized anionic charge, which offer low lattice energies, relatively small ion-ion interaction, and hence sufficient solubility and relatively large conductivity. Delocalization of the charge is achieved by electron-with drawing substituents such as -F or - CF3. Furthermore, these anions show a good electrochemical stability to oxidation. In contrast to Lewis acid-based salts they are chemically more stable with various solvents and often also show excellent thermal stability. [Pg.462]


See other pages where Lewis acid—bases is mentioned: [Pg.242]    [Pg.245]    [Pg.719]    [Pg.230]    [Pg.25]    [Pg.244]    [Pg.250]    [Pg.21]    [Pg.236]    [Pg.161]    [Pg.384]    [Pg.194]    [Pg.207]    [Pg.207]    [Pg.3]    [Pg.12]    [Pg.1128]    [Pg.611]    [Pg.957]    [Pg.132]    [Pg.228]    [Pg.229]    [Pg.232]    [Pg.233]    [Pg.234]   
See also in sourсe #XX -- [ Pg.281 ]




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Acid-base chemistry Lewis

Acid-base chemistry Lewis theory

Acid-base chemistry acids Lewis bases

Acid-base competition, Lewis

Acid-base concepts Lewis

Acid-base concepts Lewis theory

Acid-base interactions measurement Lewis acidic properties

Acid-base interactions, Lewis

Acid-base theory Lewis

Acids Lewis acid-base model

Acids Lewis acid-base reactivity

Acids and Bases The Lewis Definition

Al-based Lewis acids

Amine base-chiral Lewis acid

Amino acid derivatives Lewis bases

Anion-exchange reactions Lewis-acid-based

Bases Lewis acid-base model

Bases Lewis acid-base reactivity

Bases combined with Lewis acids

Bifunctional catalysts Lewis acid/base

Boron trifluoride Lewis acid/base complex with

Boron trifluoride Lewis acid/base complex with diethyl ether

Brpnsted acids Lewis base-, system

Carbon dioxide Lewis acid/base interactions

Carbonyl compounds Lewis acid-base interactions

Central atom concepts Lewis acids/bases

Chemical reactions Lewis acid-base

Chiral Bronsted Base-Lewis Acid Bifunctional Catalysis

Complexes, alkyne-metal Lewis acid-base

Coordination complexes, from Lewis acid-base

Coordination complexes, from Lewis acid-base arrangements

Coordination complexes, from Lewis acid-base interaction

Coordination compounds Lewis acid-base definitions

Covalent bonds Lewis acid-base interactions

Curing Lewis acids/bases

Cyclohexene Lewis acid-base reaction

Electron pair, Lewis acid-base definition

Electron-Pair Donation and the Lewis Acid-Base Definition

Equilibria Lewis acid/base

Frustrated Lewis acid-base pair catalysis

Frustrated Lewis acid-base pairs

Glass 87 Lewis acid-base reaction

Hard Lewis acids and bases

Hard-soft acid base theory bases, Lewis

Hydroxyl Groups as Bronsted Acids and Lewis Bases

Ionic Lewis acid-based

Lewis Acid-Base Behavior in Aqueous

Lewis Acid-Base Behavior in Aqueous Solution: Some Implications for

Lewis Acid-Base Behavior in Aqueous Solution: Some Implications for Metal

Lewis Acid-Base Interaction Parameter

Lewis Acid-Bronsted Base Catalyst

Lewis Acid-based Ionic Liquids

Lewis Concept of Acids and Bases

Lewis acid and base strength

Lewis acid-base , spectroscopic

Lewis acid-base adduct

Lewis acid-base adduct, formation

Lewis acid-base catalysis

Lewis acid-base character

Lewis acid-base complexes

Lewis acid-base definition

Lewis acid-base definition adduct

Lewis acid-base definition complex ions

Lewis acid-base definition complex ions and

Lewis acid-base definition defined

Lewis acid-base definition identifying

Lewis acid-base definition metal cations

Lewis acid-base definition with electron-deficient atoms

Lewis acid-base interaction electrostatic attraction/covalent

Lewis acid-base interactions bond length

Lewis acid-base interactions complex stability

Lewis acid-base interactions crown ethers

Lewis acid-base interactions nitrogen donor

Lewis acid-base interactions rings

Lewis acid-base interactions selectivity

Lewis acid-base interactions sulfur donors

Lewis acid-base interactions systematics

Lewis acid-base model

Lewis acid-base model resonance

Lewis acid-base properties

Lewis acid-base properties, metal

Lewis acid-base reaction theory

Lewis acid-base reactions

Lewis acid-base reactions, definition

Lewis acid-base system

Lewis acid-base, rate

Lewis acid-base, rate complex formation

Lewis acid-bases boron based

Lewis acid-bases mercury based

Lewis acid-bases molecular addition complexes

Lewis acid-bases stability constants

Lewis acid/base basic behaviour

Lewis acid/base basicity

Lewis acid/base bifunctional catalysts, reactions

Lewis acid/base catalysts, allylation

Lewis acid/base intramolecular

Lewis acids aluminium-based

Lewis acids and bases

Lewis acids and bases, catalyst

Lewis acids boron-based

Lewis acids iron-based

Lewis acids metal-based

Lewis acids titanium-based

Lewis acids titanium-based catalysts

Lewis acids transition metal-based

Lewis acids-bases enzymes

Lewis acids-bases multiple bonds

Lewis acids/bases strengths

Lewis acid—base reactions electrophilic addition

Lewis base organocatalysis amino acids-derived bases

Lewis base-Br0nsted acid

Lewis base-Br0nsted acid system

Lewis theory of acids and bases

Lewis, Gilbert acid-base theory

Lewis, Gilbert acids/bases

Lewis-acid-based

Lewis-type acid-base interactions

Maximum Hardness Index of Lewis Acids and Bases

Metal oxide Lewis acid-base reactions

Nitrogen Lewis acid-base interactions

Organic reactions, Lewis acid-base processes

Oxygen Lewis acid-base interactions

Reactivity Lewis acid-base

Review of Lewis Acids and Bases

Scandium-based Lewis acid

Skill 10.1 Analyzing acids and bases according to acid-base theories (i.e., Arrhenius, Bronsted-Lowry, Lewis)

Soft Lewis acid/hard Bronsted base

Soft Lewis acids and bases

Solid Bronsted acid-Lewis base catalysis

Solid surfaces, acid-base character Lewis acidity

Structure, acid-base strength Lewis

Supramolecular chemistry Lewis acid-base interactions

The Lewis Acid-Base Definition

The Lewis Acid-Base Model

The Lewis Definition of Acids and Bases

The Lewis Theory of Acids and Bases (Optional)

What Are Lewis Acids and Bases

Yttrium-based Lewis acid catalyst

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