Aromatization with aluminum chloride

Acyl cations (acylium ions) generated by treating an acyl chloride or acid anhydride with aluminum chloride attack aromatic rings to yield ketones The arene must be at least as reactive as a halobenzene Acyl cations are relatively stable and do not re arrange... 

An important use of the Friedel-Crafts alkylation reaction is to effect ring closure. The most common method is to heat with aluminum chloride an aromatic compound having a halogen, hydroxy, or alkene group in the proper position, as, for example, in the preparation of tetralin ... 

Aromatic aldazines undergo oxidative cyclization to 1-arylphthalazines (424 — 425) on treatment with aluminum chloride/triethylamine at 180°C. 

Many fluormated aromatic compounds are alkylated with alkyl halides under Fnedel-Crafts conditions For example, the intramolecular alkylation of 3-fluoro-AHchloroace-tyl)amline with aluminum chloride gives 6-fluorooxindole [5] (equation 5) Similarly, 3 -chloro-4-fluoropropiophenone affords 5-fluoroindanone [6] (equation 6)... 

Chlorobenz[d]isothiazole-l, 1-dioxide ( pseudosaccharin chloride ) (6)3,24.25, lee, 25i, 26i, 262 displays the reactivity of a cyclic imidoyl chloride263 resembling very much carboxylic acid halides. In previous sections preparation of 3, 4, 5, 13, 68, 86, 89 from 6 has been mentioned. Derivatives of 6 substituted in the phenyl ring have been described.250 Interestingly, Meadow observed231 that crude 6 and material that contained phosphorus pentachloride reacted with thiols more readily than the pure compound. In the reaction of 6 with aromatic sulfonamides, aluminum chloride had been added for activation.252... 

An oxidant. Combusdble when exposed to heat and flame. Moderate explosion hazard when exposed to heat or flame. Explosive reacdon with solid or concentrated alkali + heat (e.g., sodium hydroxide or potassium hydroxide), aluminum chloride + phenol (at 120°C), aniline + glycerol + sulfuric acid, nitric + sulfuric acid + heat. Forms explosive mixmres with aluminum chloride, oxidants (e.g., fluorodinitromethane, uranium perchlorate, tetranitromethane, sodium chlorate, nitric acid, nitric acid + water, peroxodisulfuric acid, dinitrogen tetraoxide), phosphorus pentachloride, potassium, sulfuric acid. Reacts violendy with aniline + glycerin, N2O, AgC104. To fight fire, use water, foam, CO2, dry chemical. Incompadble with potassium hydroxide. When heated to decomposidon it emits toxic flames of NOx. See also NITRO COMPOUNDS OF AROMATIC HYDROCARBONS. 

Acylation of aromatic ethers yields the corresponding keto ethers. Typical examples are found in the conversion of anisole with aluminum chloride and appropriate acyl halide to p-methoxybutyrophenone (85%) and p-methoxyphenyl benzyl ketone (84%). Mild catalysts like iodine and phosphorus pentoxide are also effective. 

This reaction was first described as a new synthesis for mixed benzoins. A solution of the aryl glyoxal in the aromatic hydrocarbon is stirred at 0° for 3-20 hours with aluminum chloride. Carbon disulfide may be used as a solvent if necessary. The yields vary from 35% to 90%. The reaction has been extended to the preparation of a-hydroxy ketones of the types RCOCHOHAr and CHjCOCOHlCHjlAr by substituting r-butylglyoxal and biacetyl, respectively, for the aryl glyoxal. 

In early work on organosulfur compounds, Duess (I) and Hil-ditch (2) reported the preparation of various aromatic disulfides by condensation reactions of thiophenol on treatment with aluminum chloride and sulfuric acid, respectively. Macallum (3) was the first to report the preparation of a phenylene sulfide polymer. His procedure involved the reaction of sulfur, sodium carbonate, and dichlorobenzene in a sealed vessel. Polymers made by this scheme generally have more than one sulfur atom between benzene rings, as indicated by the structure —( C6H4S )w-. 

Table 2.3 Aluminum chloride-lithium chloride catalyzed acylation of aromatics with acyl chlorides in 1,2-dichloroethane...

Two further methods of preparing organoboron compounds have been the subject of fairly recent detailed study, namely, reaction of boron halides with hydrocarbons and addition of boron hydrides to olefins. For instance, arylboron dihalides are formed when boron trihalides are heated with aromatic hydrocarbons, aluminum chloride, and aluminum powder,217 and phenyl-boron dibromide has been prepared analogously.218 Further, boron halides such as diboron tetrachloride and tetrafluoride add to olefins, yielding bis-(dichloroboryl) and bis(difluoroboryl) compounds 219... 

When aromatic hydrocarbons are treated with aluminum chloride the autocondensation is accompanied by side reactions (ring contraction, partial hydrogenation, etc.) reactions of phenyl and naphthyl ethers are, however, smoother, and Scholl and Seer278 obtained good yields of 4,4 -diethoxy-l,l -binaphthalene from 1-ethoxynaphthalene and aluminum chloride in nitrobenzene. 

When an aromatic compound is treated with a mixture of carbon monoxide and hydrogen chloride in the presence of aluminum chloride and copper(i) chloride, the derived aromatic aldehyde is obtained. Presumably formyl chloride is formed from the carbon monoxide and hydrogen chloride, although it is stable only as the adduct with aluminum chloride. 

EXPLOSION and FIRE CONCERNS dangerous fire and explosion hazard extremely flammable liquid NFPA rating Health 3, Flammability 3, Reactivity 1 vigorous or explosive reaction above -70°C with alkyl aluminum chlorides and aromatic hydrocarbons violently exothermic polymerization reaction with aluminum chloride, boron trifluoride, sulfuric acid incompatible or reacts strongly with nitric acid, ethylene imine, ethylenediamine, chlorsulfonic acid, oleum, sodium hydroxide combustion will produce carbon dioxide, carbon monoxide, and hydrogen chloride use carbon dioxide, alcohol foam, or dry chemical for firefighting purposes. 

Very active catalysts such as aluminum chloride often lead to significant amounts of meta products, even when the aromatic ring contains activating substituents, 0a,h,9l which is due to the thermodynamic nature of the reaction with aluminum chloride and the thermodynamic preference for the meta product. Excess catalyst and high reaction temperatures also favor more meta product. The use of BF3, sulfuric acid, ferric chloride (FeCl3) and zinc chloride (ZnCl2), in lower concentrations and at lower temperatures, gives primarily the expected ortho-para products. ... 

Cations can be formed from alcohols, and they add to aromatic rings in the usual manner. Sulfuric acid is a common catalyst for alcohols, forming an alkyl sulfate that then reacts with the aromatic substrate. 120 Alcohols are more reactive than halides, although large quantities of the Lewis acid are usually required for Friedel-Crafts reactions.I2l Alcohols form a complex with aluminum chlorides [R(H)0— A1C13], and a complicating side reaction is loss of HCl and formation of an alkyl chloride.122 a full equivalent of the Lewis acid... 

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