Lewis acids FeClj

In the presence of a Lewis acid (FeClj or FeBrj) benzene undergoes substitution reactions with halogens giving good yields. 

Alkane oxidation. Hydrocarbons are oxidized to carbonyl compounds in reasonably good yields. For example, cyclohexane gives cyclohexanone (60%). The reaction is greatly accelerated by the addition of Lewis acids (FeClj, ZnCL, etc.). 

Cyclopropane is one notable exception, as it undergoes electrophilic addition reactions. Cyclopropane is more reactive than propene toward addition of acids such as HBr and HCI but is less reactive towards addition of CI2 and Br2, so a Lewis acid, FeClj, is needed to catalyze halogen addition (Scheme 4.25). 

Lewis acid CaCl3 InClj Aid 3 FeClj SbCl5 AgOTf... 

In simple mechanisms you encountered in Organic Chemistry 1, methyl and primary carbocations were seriously frowned upon. However, AICI3 and FeClj are such good Lewis acids that even these elusive primary Ccirbocations can form. You should still avoid primary ccirbocations in mechanisms. 

If these reactions are carried out in CS2, fullerene-Lewis acid complexes precipitate [91], The complexation behavior of Cjq and C q is different, with C q complexing much more strongly than Cjq. This phenomenon was taken advantage of in separating the fullerene mixtures. Other Lewis acids that form CSj-insoluble complexes are AlBrj, TiCl4, SnCl4 and FeClj. The parent fullerenes can be recovered from the Lewis acid complexes by reaction with ice water [92]. 

If solutions of CgQ in aromatic hydrocarbons are treated with Lewis acids, such as AICI3, AlBrj, FeBrj, FeClj, GaClj or SbClj, then a fullerylation of aromatics takes place (Scheme 8.11) [66, 88, 90, 91], In this case, the Lewis acid serves as a catalyst and increases the electrophilicity of the fullerene. Mixtures of polyarylated fullerenes are obtained. Depending on the reaction conditions and the aromatic used for the fullerylation, up to 16 aryl groups are covalently bound to the fullerene core [66, 88,... 

Under the influence of a Lewis acid, Cjq can be arylated via a Eriedel-Crafts reaction (see Section 8.6). A similar reaction occurs with CggEjg where ipso substitution of fluorine atoms takes place [68]. The fluorofullerene is treated with FeClj in benzene for two weeks (Scheme 9.8). Electrophilic substitution leads to arylated C5QFjg Ph with n = 1-3. Probably due to steric reasons the 5-substitution is not observed in this arylation. 

A variety of catalysts, including other Lewis acids such as FeClj and BF3, and the protic acids HF, phosphoric acid and sulfuric acid, has been used. In reactions using alcohols, the favoured catalyst is BF3 HF is often used in reactions involving alkenes. 

E4.43 Equation (b) is better in explaining the observ ations described in the exercise. Most notably it contains the Lewis acid-base adduct [FeCblOPC 1,3)4] in which OPCI3 is a Lewis base and coordinates via its O atom, consistent with vibrational data. It also has the Fe Clb/fFeCy (i.e., red/yellow) equilibrium. The titration would have to start in either case from a concentrated (red) solution, and the equivalence point at 1 1 mole ratio FeClj/Et4NCI can be explained based on the reaction ... 

The conventional method for preparation of these aromatic ketones involves reaction of the aromatic hydrocarbon with a carboxylic acid derivative in the presence of a Lewis acid (AICI3, FeClj, BF3, ZnCl2, TiCy or Brpnsted acids (poly-phosphoric acid, FIF). The major drawback of the Friedel-Crafts reaction is the need to use a stoichiometric quantity of Lewis acid relative to the ketone formed. This stoichiometric quantity is required because the ketone (product of the reaction) forms a stable stoichiometric complex with the Lewis acid. The decomposition of this complex is generally performed with water, leading to total destruction and loss of the Lewis acid. 

For preparative purposes, a Lewis acid such as AICI3 or FeClj is often used to catalyze chlorination. Chlorination of benzene using AICI3 is overall third order. ... 

Oxidation. Primary alcohols are oxidized to aldehydes under solvent-free conditions with this reagent and aluminum chloride as catalyst. Reaction in the presence of other Lewis acids including FeClj, BiClj, and ZnCl2 are less efficient. 

Cycloaddition of allenes to alkenes. This cycloaddition to give methylenecyclobutanes (3) can be realized in the presence of certain Lewis acids as catalysts (listed in approximate order of decreasing reactivity) C2H5AICI2, GaCls, AlBrj, AICI3, FeClj. 

Lithiated polystyrene resins can be obtained either via convenient bromine-lithium exchange reaction using nBuLi starting from 4-bromo-substituted polystyrene 102,111-115 qj. jjy direct lithiation of polystyrene using nBuLi in cyclohexane in the presence of TMEDA 11L116 pjjjj method, however, yields a mixture of para- and meta isomers. The bromination of microporous resins in the presence of the Lewis-acid catalysts was carried out in the dark whereby the degree of functionalisation could conveniently be controlled by the amount of bromine used in the reaction.iii Macroreticular resins were brominated using Br and FeClj or stoichiometric amounts of thallium acetate as Lewis acid catalysts. 2 ... 

The reaction of fullerenes with the Lewis acid BH3 were used to synthesize hydrogenated fullerenes (Scheme 7). Also, other Lewis acids, for example AlBr3, TiCl4, SnCl4, and FeClj, have been allowed to react with Cgg [172-174]. If these reactions are carried out in CS2,fullerene-Lewis acid complexes precipitate. 

FeClj acts as Lewis acid and abstracts Cl from Cl and thus helps in the formation of CF (electrophile)... 

The Schmidt reaction of ketones with hydrazoic acid requires the presence of an acid catalyst. Sulfuric acid is the most common catalyst, but Lewis acids have also been utilized. Hydrazoic acid is usually made in situ by treatment of sodium azide with sulphiuic acid. The strongly acidic conditions can bring about decomposition of acid-sensitive substrates and result in undesired by-products. However, the Schmidt reaction can be conducted under mild conditions. For example, various ketones are converted to the corresponding amides or lactams using trimethylsilyl azide or sodium azide in the presence of FeClj in dichloroethane at room temperature. ... 

Halogenation (Section 22.1 A) The electrophile is a halonium ion formed as an ion pair by interaction of chlorine or bromine with a Lewis acid. The mechanism involves an initial reaction between Clj and FeClj to generate a molecular complex that can rearrange to give a C1+, FeCl " ion pair. The C1+ reacts as a very strong electrophile with the weakly nucleophilic aromatic 77 cloud to form a resonance-stabilized cation intermediate that loses a proton to give the aryl chloride product. 

Metal oxides are usually utilized in their pure form or in different mixtures as solid catalysts in fine chemical preparation since they are commercially available or easily synthesized, they are stable toward moisture, and their properties can be tailored by doping with convenient metal ions [74]. Dimethylbenzophenones can be obtained in high yield (88-97%) by reaction between benzoyl chloride and the three isomeric xylenes (xylene/benzoyl chloride ratio=1.5) in the presence of iron(III) oxide. Various researchers have observed leaching of FeClj (produced by reaction of iron oxide with HCl) into solution, suggesting a possible catalytic contribution from this homogeneous iron-based Lewis acid. 

The catalytic efficiency of various Lewis acids, such as InClj, BiClj, ZnClj, and FeClj was tested for this transformation. The reactions were not clean with the above Lewis acids and also the products were obtained as a mixture of isomers while molecular iodine was found to be the most effective. In the absence of iodine, the reactions did not proceed even after 12 h indicating that molecular iodine is essential to fadhtate the reaction. Out of the solvents studied, DCM appeared to give the best results. 

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