Friedel-Crafts reaction, aromatic hydrocarbons

From Hydrocarbons, Friedel-Craft.—The aromatic hydrocarbons yield ring carboxy acids by other reactions than those effecting oxidation of a side chain. Carbon dioxide may be introduced directly into a benzene ring, thus converting a hydrogen into.carboxyl. This may be accomplished in the presence of aluminium chloride, Friedel-Craft reagent. 

Methods of producing B —C bonds include hydroboration, nucleophilic displacement at a boron atom in BX., (X = halogens or B(0R>3) by e.g. a Grignard reagent, and a psewiio-Friedel-Crafts reaction with an aromatic hydrocarbon, BX3, and AICI3. 

TTie true ketones, in which the >CO group is in the side chain, the most common examples being acetophenone or methyl phenyl ketone, C HjCOCH, and benzophenone or diphenyl ketone, C HjCOC(Hj. These ketones are usually prepared by a modification of the Friedel-Crafts reaction, an aromatic hydrocarbon being treated with an acyl chloride (either aliphatic or aromatic) in the presence of aluminium chloride. Thus benzene reacts with acetyl chloride... 

The Friedel-Crafts Reaction, in which an aromatic hydrocarbon reacts with an alkyl halide under the influence of aluminium chloride ... 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Aromatic hydrocarbons substituted by alkyl groups other than methyl are notorious for their tendency to disproportionate in Friedel-Crafts reactions. This tendency has previously limited the application of the isomerization of para- or ortho-) m ky -benzenes to the corresponding meta compounds. At the lower temperature of the present modification, disproportionation can be minimized. 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

Friedel-Crafts reaction org chem A substitution reaction, catalyzed by aluminum chloride in which an alkyl (R —) or an acyl (RCO —) group replaces a hydrogen atom of an aromatic nucleus to produce hydrocarbon or a ketone. fre del krafs re.ak shan ... 

Unsaturated 5(4H)-oxazolones undergo a Friedel-Crafts reaction with aromatic hydrocarbons in the presence of a Lewis acid. In particular, a 2-aryl-4-benzylidene-5(4H)-oxazolone 598 reacts with o- or p-xylene in the presence of aluminum chloride via ring opening and subsequent dearylation to yield 599 as indicated in Scheme 7.191. ... 

At higher temperatures, C—H and C—C bonds may be similarly broken. Thus, zeolite catalysts may be used for (i) alkylation of aromatic hydrocarbons (cf. the Friedel-Crafts reactions with AICI3 as the Lewis acid catalyst), (ii) cracking of hydrocarbons (i.e., loss of H2), and (Hi) isomerization of alkenes, alkanes, and alkyl aromatics. 

A short review in Chinese covers Friedel-Crafts reactions of alkenyl halides with aromatic hydrocarbons.49 High yields of the allylated aromatic products have been... 

Crystalline adducts between antimony trichloride and aromatic hydrocarbons have been known since the nineteenth century (272,273) and have been investigated in detail since the 1970s (274). Since such adducts have been postulated as intermediates in Friedel-Crafts reactions, their structure is of interest. 

A small perfectly mixed discontinuous reactoms used at laboratory scale to conduct the Friedel-Crafts reaction Ar-H -i- RCl —> Ar-R -i- HCl. Three factors and two or more levels of each parameter have been used in an experimental plan in order to separate and compare their influence on the aromatic hydrocarbon conversion. The following factors and levels have been used ... 

Polyfluoroalkylation Some of the chemistry of polyfluoroalkyl anions, generated by reaction of fluoroalkenes with fluoride ion, was discussed in Chapter 7, where the analogy between the role of fluoride ion in fluorocarbon chemistry and the role of the proton in hydrocarbon chemistry was emphasised. This analogy has been extended to include reactions of polyfluorinated anions, generated in the same way, with activated poly-fluoro-aromatic systems in what may be regarded as the nucleophilic counterpart of Friedel-Crafts reactions [119] (Figure 9.50). 

These compounds are prepared by the aid of the Friedel-Craft reaction. Dichloro-p-arsinobenzoyl chloride readily condenses with aromatic hydrocarbons and phenyl ethers in carbon disulphide solution... 

From Hydrocarbons.—An interesting method sometimes applicable for the preparation of aromatic aldehydes is from the hydrocarbons by means of the Friedel-Craft reaction, as modified by Gattermann and Koch with carbon monoxide and hydrochloric acid in the presence of CuCl. In this reaction formyl chloride, which is unknown in the free condition, is probably first formed by the union of the carbon monoxide and hydrochloric acid. 

Aromatic hydrocarbons, such as benzene add to alkenes using a ruthenium catalyst a catalytic mixture of AuCVAgSbFs, or a rhodium catalyst, and ruthenium complexes catalyze the addition of heteroaromatic compounds, such as pyridine, to alkynes. Such alkylation reactions are clearly reminiscent of the Friedel-Crafts reaction (11-11). Palladium catalysts can also be used to for the addition of aromatic compounds to alkynes, and rhodium catalysts for addition to alkenes (with microwave irradiation). " Note that vinyhdene cyclopropanes react with furans and a palladium catalyst to give aUylically substituted furans. ... 

Aromatic hydrocarbons are best identified and characterized by uv and nmr spectroscopy, but the Friedel-Crafts reaction produces a characteristic color with certain aromatic hydrocarbons. 

Commercial benzene (bp 80°) and toluene (bp 111°) contain thiophene and methylthiophene as the main impurities. These impurities are more reactive than benzene or toluene in aromatic substitution reactions and therefore should be removed before using the material for reactions such as the Friedel-Crafts reaction. The thiophenes may be removed by shaking or stirring the hydrocarbon with one-tenth its volume of concentrated sulfuric acid for one-half hour. Because of the reactivity of toluene, the temperature should be maintained under 35° by occasional cooling. This treatment is, however, rarely necessary since thiophene-free benzene and toluene are commercially available at a reasonable cost. 

PREPARATION OF AROMATIC HYDROCARBONS BY THE FRIEDEL-CRAFTS REACTION... 

Introduction. The object of this and of the two following experiments is to illustrate the application of the Friedel-Crafts reaction to the synthesis of organic compounds. In the present experiment the preparation of aromatic hydrocarbons will be considered. 

The Friedel-Crafts reaction can also be used for the preparation of the homologous aromatic hydrocarbons, since in place of the add-chloride, halogen alkyls may be caused to act on the hydrocarbons 1... 

The conventional method for preparation of these aromatic ketones involves reaction of the aromatic hydrocarbon with a carboxylic acid derivatives using a Lewis acid (AICI3, FeCb, BF3, ZnCb, TiCl4) or Bronsted acids (polyphosphoric acid, HF). The major drawback of the Friedel-Crafts reaction is the need to use a stoicheiometrical quantity of Lewis acid relative to the formed ketone. This quantity is required due to the fact that the... 

Thiophen Analogues of Polycyclic Aromatic Hydrocarbons Analogues of Anthracene and Phenanthrene. - Keto-enol tautomerism in a naphtho- and several anthra-thiophen systems [such as (241) (242)] has been studied. The system (241) (242) was obtained via the Friedel-Crafts reaction of thiophen with naphthalene-2,3-dicarboxylic anhydride followed by ring-closure. A [c] -fused system was similarly obtained by starting from... 

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