Aluminum chloride catalytic effect

The reduction of 4-chloro-4-methyltetrahydropyran with triethylsilane requires more than a catalytic amount of aluminum chloride. No 4-methyltetrahydropyran is obtained after 20 hours at room temperature even when 0.75 equivalents of the catalyst is used, but a 92% yield is obtained after only 30 minutes when two equivalents of catalyst and three equivalents of triethylsilane are used.136 146 This is presumably a result of the ability of the Lewis acid to coordinate at the ring oxygen as well as at the chlorine. The introduction of alkyl groups at C2 appears to introduce enough steric hindrance near the ring oxygen to enable less than one equivalent of aluminum chloride to effect reduction, but also makes the products unstable to the reaction conditions so that the synthetic yields decline compared with the unsubstituted substrate.136... 

H2SnClg 6H20, CISO H + CH OH, CH COOH, as well as ben2ene-, naphthalene-, and -toluenesulfonic acids (44). Zinc chloride is probably the most frequentiy used catalyst. Its activity is sometimes increased by fusion with a small amount of aluminum chloride. In other instances, however, sufficient catalytic effect is obtained with a mineral acid alone. 

Solid Superacids. Most large-scale petrochemical and chemical industrial processes ate preferably done, whenever possible, over soHd catalysts. SoHd acid systems have been developed with considerably higher acidity than those of acidic oxides. Graphite-intercalated AlCl is an effective sohd Friedel-Crafts catalyst but loses catalytic activity because of partial hydrolysis and leaching of the Lewis acid halide from the graphite. Aluminum chloride can also be complexed to sulfonate polystyrene resins but again the stabiUty of the catalyst is limited. 

Lewis acids such as zinc chloride, boron trifluoride, tin tetrachloride, aluminum chloride, methylaluminum dichloride, and diethylaluminum chloride catalyze Diels-Alder reactions.22 The catalytic effect is the result of coordination of the Lewis acid with the dienophile. The complexed dienophile is more electrophilic and more reactive toward electron-rich dienes. The mechanism of the addition is believed to be concerted and enhanced regio- and stereoselectivity is often observed.23... 

Jensen et al.16 also studied the decomposition of 5-ethoxythiatriazole in dibutyl phthalate solution in the presence of trichloroacetic acid, tripentylamine, 4-benzylpyridine, anhydrous aluminum chloride, or trinitrobenzene, but practically no effect on the reaction rate was observed. However, later experiments have shown that the decomposition can indeed by enhanced catalytically by Lewis acids under conditions where the catalyst is not sequestered by complex formation with the solvent.19 Thus the addition of aluminum chloride to 5-phenylthiatriazole in benzene causes a brisk evolution of nitrogen at room temperature, and if instead boron tribromide is added, a rather violent reaction sets in. However, when esters or ethers are used as... 

The reaction conditions generally seem to be more critical with aluminum chloride than with stannic chloride. Yields, perhaps as a result, are more often hard to duplicate. These facts are doubtless due in part to the greater reactivity of aluminum chloride and to the difficulty commonly experienced in obtaining samples of this reagent which do not vary in catalytic effect. A pronounced influence of the grade of the aluminum chloride already has been mentioned. 

Use of Metal Halides. Metal halides and particularly izinc and aluminum chlorides have been found to be effective dehydrochlorinating agents. When pentachloroethane is heated with aluminum chloride, tetrachloreth-ylene is obtained. The pentachloroethane is fed continously into a mixture of tetrachloroethylene and aluminum chloride (or metal aluminum particles) at 120 C. The chloroolefin distills over with hydrogen chloride, and the metal halide becomes converted to an organo aluminum chloride complex of diminishing catalytic activity. Fresh catalyst must consequently be added periodically to maintain high conversion rates. 

AlCU Complex Alkylation. Another catalyst used for paraffin alkylation is a liquid complex made from aluminum chlotide in a hydrocarbon solvent. The complex contains 55-62 per cent by weight aluminum chloride and is understood to-be a kerosene selected for certain impurities which enhance the catalytic effect of the aluminum chloride. 

A number of LrCwis acids have been shown to effect disproportionation of hexaorganoditin compounds. Treatment of hexaethylditin with aluminum chloride in catalytic amounts results in the formation of tetraethyltin, metallic tin, and a diethyltin polymer. 

Lewis acids, particularly aluminum chloride, have been noted to catalyze Diels-Alder cycloadditions.The catalytic effect is attributed to coordination of the Lewis acid with the dienophile. The complexed dienophile is then more electron-... 

It is of interest to note that in several instances the effect of a catalyst such as aluminum chloride or boron fluoride is enhanced by the presence of an acidic assistant. Alkylation by olefins with aluminum chloride as a catalyst is favored by the presence of anhydrous hydrogen chloride, and the condensation of primary alcohols with benzene uting boron fluoride is possible only with the aid of an. assistant such as phosr phoric anhydride, benzenesulfonic acid, or sulfuric acid. It has been foimd also that chlorides of tin, silicon, or titanium increase the catalytic activity of aluminum chloride, whereas ferric chloride decreases the... 

This reaction occurs with 100 % atom economy. Unlike the standard Friedel-Crafts type of reaction, which utilize the catalytic effect of Lewis acid-type acidic halides, particularly aluminum chloride, AICI3, the photochemical process does not require moisture- and air-sensitive, potentially reactive catalytic substances. 

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