Acid chlorides AICI3 complexes

This reaction was first reported by Baddeley in 1930s. It is the migration of alkyl groups in polyalkylbenzenes or polynuclear aromatic compounds in the presence of anhydrous aluminum chloride or the mixture of protonic acid and Lewis acid. In one of Badde-ley s experiments, when 1,3,4-tri-n-propylbenzene was warmed with AICI3 at 100°C, the 1,3,5-tri-n-propyl was formed, along with the lower and higher alkylated benzenes. After extensive studies, it was found that the amount of a-isomer can be reduced by the addition to the reaction mixture of a variety of substances (e.g., nitrobenzene and excess acid chloride) that complex strongly with aluminum chloride. Likewise, less a-isomer has been observed when this reaction is carried out in nitrobenzene. In addition, isomerization of hindered aromatic ketones occurs if the ketones are melted with an excess amount of aluminum chloride and sodium chloride. ... 

Friedel Crafts acetylation of butadiene complex 56 proceeds smoothly to give a mixture of 1-acetyldienes 58 and 59 via the cationic 7r-allyl complex 57 [16]. Intramolecular Friedel-Crafts acylation with the acid chloride of the diene complex 60, promoted by deactivated AICI3 at 0 °C, gave the cyclopentanones. The (Z)-dienone complex 61 was the major product and the ( )-dienone 62 the minor one [17]. Acetylation of the 1,3-cyclohexadiene phosphine complex 63 proceeded easily at —78°C to give the rearranged complex 65 in 85% yield. Without phosphine coordination, poor results were obtained [18,19], In this reaction, the acetyl group at first coordinates to Fe, and attacks at the terminal carbon of the diene from the same... 

Carbonyl groups form complexes or intermediates with Lewis acids like AICI3, BF3, and SnCl4. For example, in the Friedel-Crafts acylation reaction in nonpolar solvents, an aluminum chloride complex of an acid chloride is often the acylating agent. Because of the basicity of ketones, the products of the acylation reaction are also complexes. For more detail on electrophilic aromatic substitution, see Section 7. 

Acylation of aromatic compounds (Friedel-Crafts, FC, acylation), of great industrial interest, suffers from an important catalysis problem [69]. Most of the Lewis acids used as catalysts (traditionally metal chlorides such as AICI3) complex preferentially with the ketone produced instead of with the acylating agent [70] (Scheme 9.20). Except for bismuth (III) chloride with acid chlorides, rarely does a metal chloride complex preferentially with the acylating agent [71, 72]. 

Finally, it has been reported that sulphur dichloride and trichloro-methanesulphenyl chloride give 1 1 and 2 1 complexes with Lewis acids (SbClg,AICI3,FeClg) with a salt-like behaviour . The instability of the complexes made a full characterization unfeasible. 

Cyclopentadienyl complexes show aromatic properties. This is the origin of the names metallocenes, ferrocene, etc. For example, the Friedel-Crafts acylation proceeds very easily. Ferrocene is acylated 3.3 x 10 times faster than benzene. The acylating reagents are the organic acid chlorides and acid anhydrides. The reaction is catalyzed by the typical Friedel-Crafts catalysts BF3, AICI3, etc. 

Nitroparaffins afford an unique reaction medium for Friedel-Crafts reactions since these solvents will dissolve Lewis acid catalysts such as anhydrous aluminum chloride (AICI3), boron trifluoride (BF3), titanium tetrachloride (TiCl4), and stannic tetrachloride (SnC ). The role of nitromethane as a metal stabilizer for various chlorinated and fluorinated solvents involves its ability to complex with metal salts like aluminum chloride from the solvent-metal reaction. 

Acid chlorides react with benzene under the influence of an equivalent (not a catalytic amount) of AICI3. A molecule of AICI3 is needed for each molecule of product. By now it should be easy to write a general mechanism. A complex is first formed with AICI3. But which complex Unlike alkyl chlorides, acid chlorides contain two nucleophilic sites, the oxygen and chlorine atoms. The evidence is that both complexes are formed, and that the two are in equilibrium. The resonance-stabilized acylium ion can be formed by dissociation of the complex (Fig. 14.43). 

The Friedel-Crafts reactions succeed because relatively stable carbocations can be formed by the reaction of aluminum chloride (an exceptionally strong Lews acid with which an alkyl halide will react) in solvents that are nonnucleophilic. The strongest nucleophile available in the reaction vessel is benzene, which attacks the cation to start the Friedel-Crafts reaction. If stable carbocations cannot be formed, as with methyl chloride or ethyl chloride, the AICI3 complexes can also alkylate benzenes. 

Friedel-Crafts acylation generally involves reaction of an acid halide with a Lewis acid catalyst such as AICI3, SbFs, or BF3. Acid anhydrides are employed in some cases. As in alkylations, the reaction intermediate may be a dissociated organic cation (acylium ion) or a complex of the acid chloride and Lewis acid. " ... 

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... 

Carboxylation of aromatics with carbon dioxide with AI2CI,/AI has been studied by Olah, Prakash, and co-workers425 and shown to be a chemoselective process to give aromatic carboxylic acids in good to excellent yields (20-80°C, CO pressure = 57 atm). Two possible mechanistic pathways with the involment of organoaluminium intermediates and complexes of C02 with AICI3 were postulated. On the basis of extensive experimental studies and theoretical calculations, the authors concluded that the most feasible mechanism involves CO2 activated with superelectrophilic aluminum chloride. Complex 116 reacts with aromatics in a typical electrophilic substitution. 

Trans acylations have been encountered in the acylation of 2-acylthiophenes. Thus the action of benzoyl chloride on 2-acetylthiophene in presence of excess AICI3 has led to a complex mixture, from which 2-benzoyl-, 2,4-dibenzoyl- and 2,5-dibenzoyl-thiophene were isolated (73ZOR1959). Other examples of ipso acylation including acyl-debromination and acyl-de-r-butylation have been recorded. Unexpected products have been reported in some intramolecular cyclizations. Thus cyclization of the acid (103) leads to (104) and not (105) (63AHQD1). Acid-catalyzed cyclization of ylidene-malononitriles has been reported (75JOC1840). Yields are in the range 30-60% (Scheme 19). 

The oldest method of alkylation with ethylene is the liquid phase reaction using anhydrous aluminum chloride as the catalyst. This reaction is a form of the classic Friedel-Crafts reaction and was discovered in 1879 by Balsohn. Most Lewis and Bronsted acids are known to be active for olefin alkylations. Alkylation by H2SO1, and H3PO1, was first shown by Ipatieff, et al, in 1936 who extended the reaction to isoparaffins. For the liquid phase alkylation of benzene with ethylene, however, aluminum chloride is preferred over the other acids, although a co-catalyst or promoter is usually needed to obtain efficient alkylation. AICI3 when dissolved in benzene containing some HCl forms a complex which can be simply described as ... 

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