The Action of the Catalyst Couple Aluminum Chloride—Hydrogen Chloride on Toluene at Low Temperatures; the Nature of Friedel—Crafts Complexes<sup>1,2</sup>

Brown, Herbert C.; Pearsall, Howard

doi:10.1021/ja01121a049

Cited by 51 publications

(15 citation statements)

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“…An older study of proton transfer to the intermediate strength bases, pyridine and 2-methylpyridine, from HCl, and HCl enhanced by AlCl 3 to give both AlCl 4 À and Al 2 Cl 7 À anions, showedt he Al 2 Cl 7 À anions to be even more weakly basic than AlCl 4 À ,p roviding an electronic environment for the > NH protont hat is close to that of ap yridiniumc ation in free space. [77] For economic reasons, we have been unable to include in our study the "strongest acid" identified by the Reed group, carborane acid. [77] For economic reasons, we have been unable to include in our study the "strongest acid" identified by the Reed group, carborane acid.…”

Section: Resultsmentioning

confidence: 99%

“…[49] Such observations help in understanding not only the exceptional properties of chloroaluminate ionic liquids [72,76] (and their chloroferrate relatives) [73] but also the stabilization (at low temperatures)o ft oluenium cations in the presence of AlCl 4 À and Al 2 Cl 7 À anions, in the classic work of Brown and Pearsall. [77] For economic reasons, we have been unable to include in our study the "strongest acid" identified by the Reed group, carborane acid. [78] We were also unable to include carborane anions' rivals in low basicity,t he very weakly coordinating anions of highly fluorinated aluminates [Al(OR f ) 4 ] À , [79] because of cost and availability.C omparable acidity might be found in the protonated form of the giant bisperfluoropinacolatoborate anion "LiBPFPB" (24 fluorine atoms).…”

Section: Resultsmentioning

confidence: 99%

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On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

Hasani

Yarger

Angell

2016

Chemistry A European J

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The need for reliable means of ordering and quantifying the Lewis basicity of anions is discussed and the currently available methods are reviewed. Concluding that there is need for a simple impurity-insensitive tool, we have sought, and here describe, a new method using NMR spectroscopy of a weak base, a substituted urea, 1,3-dimethyl-2-imidazolidinone (DMI), as it is protonated by Brønsted acids of different strengths and characters. In all cases studied the product of protonation is a liquid (hence a protic ionic liquid). NMR spectroscopy detects changes in the electronic structure of the base upon interaction with the proton donors. As the proton-donating ability, that is, acidity, increases, there is a smooth but distinct transition from a hydrogen-bonded system (with no net proton transfer) to full ionicity. The liquid state of the samples and high concentration of nitrogen atoms, despite the very low natural abundance of its preferred NMR-active isotope ((15) N), make possible the acquisition of (15) N spectra in a relatively short time. These (15) N, along with (13) C, chemical shifts of the carbonyl atom, and their relative responses to protonation of the carbonyl oxygen, can be used as a means, sensitive to anion basicity and relatively insensitive to impurities, to sort anions in order of increasing hydrogen bond basicity. The order is found to be as follows: SbF6 (-) ClO4 (-) >FSO3 (-)

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

Hasani

Yarger

Angell

2016

Chemistry A European J

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“…The study of modern ionic liquids originated from high-temperature inorganic molten salts (studied as heat transfer fluids and electrolytes), which lead to lower melting organic salts, especially chloroaluminate(III) ILs (Fig. 1, left [12,16]. This naturally led to studies of Friedel-Crafts chemistry in the [C 2 mim]Cl-AlCl 3 system [17], which may be considered the starting point of Lewis acid catalysis in chlorometallate ILs, with over 400 citations to date.…”

Section: Chlorometallate Ionic Liquids 21 Historical Contextmentioning

confidence: 99%

Lewis Acidic Ionic Liquids

Brown

Hogg

Swadźba‐Kwaśny

2017

Topics in Current Chemistry Collections

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Until very recently, the term Lewis acidic ionic liquids (ILs) was nearly synonymous with halometallate ILs, with a strong focus on chloroaluminate(III) systems. The first part of this review covers the historical context in which these were developed, speciation of a range of halometallate ionic liquids, attempts to quantify their Lewis acidity, and selected recent applications: in industrial alkylation processes, in supported systems (SILPs/SCILLs) and in inorganic synthesis. In the last decade, interesting alternatives to halometallate ILs have emerged, which can be divided into two subsections: (1) liquid coordination complexes (LCCs), still based on halometallate species, but less expensive and more diverse than halometallate ionic liquids, and (2) ILs with main-group Lewis acidic cations. The two following sections cover these new liquid Lewis acids, also highlighting speciation studies, Lewis acidity measurements, and applications.

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“…Electrophilic substitution, considered to be the most characteristic reaction of aromatic systems, is typically described in textbooks, monographs, and reviews by the two-stage S E Ar mechanism depicted in Fig. 1 (5)(6)(7)(8)(9)(10)(11). Arenium ion (σ-complex) intermediates are often ascribed to Wheland (9) inaccurately, since Pfeiffer and Wizinger (10) laid out the principles of such species for bromination in 1928.…”

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confidence: 99%

“…Arenium ion (σ-complex) intermediates are often ascribed to Wheland (9) inaccurately, since Pfeiffer and Wizinger (10) laid out the principles of such species for bromination in 1928. Following Brown and Pearsall (11), they are widely believed to have σ-complex structures. Arenium ions (σ-complexes) (9)(10)(11) are widely accepted to be obligatory intermediates and are used to rationalize ortho/para vs. meta position orientation preferences (6)(7)(8)(9)(10)(11).…”

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confidence: 99%

Arenium ions are not obligatory intermediates in electrophilic aromatic substitution

Galabov

Koleva

Hadjieva

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Our computational and experimental investigation of the reaction of anisole with Cl 2 in nonpolar CCl 4 solution challenges two fundamental tenets of the traditional S E Ar (arenium ion) mechanism of aromatic electrophilic substitution. Instead of this direct substitution process, the alternative addition-elimination (AE) pathway is favored energetically. This AE mechanism rationalizes the preferred ortho and para substitution orientation of anisole easily. Moreover, neither the S E Ar nor the AE mechanisms involve the formation of a σ-complex (Wheland-type) intermediate in the rate-controlling stage. Contrary to the conventional interpretations, the substitution (S E Ar) mechanism proceeds concertedly via a single transition state. Experimental NMR investigations of the anisole chlorination reaction course at various temperatures reveal the formation of tetrachloro addition by-products and thus support the computed addition-elimination mechanism of anisole chlorination in nonpolar media. The important autocatalytic effect of the HCl reaction product was confirmed by spectroscopic (UV-visible) investigations and by HCl-augmented computational modeling.organic chemistry | reaction mechanisms | alternative computed routes | autocatalysis

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The Action of the Catalyst Couple Aluminum Chloride—Hydrogen Chloride on Toluene at Low Temperatures; the Nature of Friedel—Crafts Complexes^1,2

Cited by 51 publications

References 1 publication

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

Lewis Acidic Ionic Liquids

Arenium ions are not obligatory intermediates in electrophilic aromatic substitution

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The Action of the Catalyst Couple Aluminum Chloride—Hydrogen Chloride on Toluene at Low Temperatures; the Nature of Friedel—Crafts Complexes1,2

Cited by 51 publications

References 1 publication

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity

Lewis Acidic Ionic Liquids

Arenium ions are not obligatory intermediates in electrophilic aromatic substitution

Contact Info

Product

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The Action of the Catalyst Couple Aluminum Chloride—Hydrogen Chloride on Toluene at Low Temperatures; the Nature of Friedel—Crafts Complexes^1,2