Aluminum fluoride Lewis acid

In a generalized sense, acids are electron pair acceptors. They include both protic (Bronsted) acids and Lewis acids such as AlCb and BF3 that have an electron-deficient central metal atom. Consequently, there is a priori no difference between Bronsted (protic) and Lewis acids. In extending the concept of superacidity to Lewis acid halides, those stronger than anhydrous aluminum chloride (the most commonly used Friedel-Crafts acid) are considered super Lewis acids. These superacidic Lewis acids include such higher-valence fluorides as antimony, arsenic, tantalum, niobium, and bismuth pentafluorides. Superacidity encompasses both very strong Bronsted and Lewis acids and their conjugate acid systems. 

The Eries rearrangement of phenol esters gives a mixture of 2- and 4-acylphenols (56). The reaction is cataly2ed by Lewis acids such as aluminum chloride or by Brmnsted acids like hydrogen fluoride. This reaction is used in the production of 4-hydroxyacetophenone [99-93-4] a raw material for... 

Fluorides with fluorine-phosphorus bonds also react with Lewis acids tert-Butylpentafluorocyclotriphosphazenes are arylated in the presence of aluminum chlonde [26] (equation 18)... 

A wide range of Lewis acids have been used in the extensive studies of the conversion of perfluoro(2-melhyloxirane)28 into hexafluoroacetone. including antimony(V) fluoride,31-32 aluminum trichloride,30 aluminum chlorofluoride (from A1C1, and CFClj).23-33 alumina pre-... 

If lithium aluminum deuteride is used, then controlled introduction of deuterium is achieved84. Other solvents such as THF or DME have also been employed76. Under normal circumstances, fluorides are inert but vinyl fluorides may be selectively replaced (equation 8)85-87. Other fluorides may also been reduced if cerium salts or other Lewis acids are added88. 

Although it is perhaps not used as extensively as aluminum chloride, aluminum bromide is also widely used as a Lewis acid catalyst. Aluminum fluoride is used in the preparation of cryolite, Na3AlF6, which is added to alumina to reduce its melting point and increase its electrical conductivity in the electrolytic production of aluminum. One reaction that can be employed to produce the fluoride is... 

In another gas-phase process, chloroformates can be converted with a large excess of anhydrous hydrogen fluoride in the presence of a Lewis acid catalyst, which may be steel, chromium(lll) oxide, oxides and fluorides of aluminum and the fluorides of cerium, lanthanium or magnesium. 

Fluorine-containing aldehydes, ketones and acid fluorides undergo photoinitiated cycloaddition reactions with fluorinated alkenes to give oxetanes.90 91 The addition of hexafluoroacetone (11) to fluoroalkenes can also be performed in the presence of the Lewis acid, aluminum chloride fluoride.92-1 22-1 23 Unlike the photochemical cycloaddition of hexafluoroacetone with trifluoroethene, the Lewis acid catalyzed addition is regioselective.92 Fluorooxetanes (c. g., 14) have also been synthesized by the addition of formaldehyde to fluoroalkenes in hydrogen fluoride.94 Examples of the formation of fluorooxetanes by [2 + 2]-cycloaddition reactions arc-given in Table 8. 

The combination of LAH with Lewis acid has a powerful reducing ability. The use of aluminum chloride or cerium chloride under more drastic conditions enables primary alkyl fluorides to be converted to the corresponding saturated hydrocarbons in good to excellent yields. 

Nucleophilic addition of the trifluoromethyl group to aldehydes, ketones and other carbonyl compounds leads primarily to the corresponding trimethylsilyl ether this must subsequently be hydrolyzed to the alcohol. Because typical reaction conditions are very mild, the method is widely applicable, even for sensitive substrates. In contrast with most other methods, fluoride-induced perfluoroalkylation via silicon compounds also works for enolizable carbonyl compounds. With c(, -un-saturated substrates 1,2-addition directly to the carbonyl group is strongly preferred [64b]. If the oxygen is coordinated to a bulky Lewis acid, for example aluminum tri(2,6-bis(tert-butyl)phenoxide (ATPH), the 1,4-addition products are obtained selectively [73f] (Scheme 2.128). 

A number of oi ganoaluminum reagents, especially Me2AlCl, have been found to be effective catalysts for reactions of enol silyl ethers with aldehydes.It is possible that in these reactions, aluminum enol-ates may be involved as the intermediates. Similarly, bismuth trichloride has been reported to be an efficient catalyst.Since BiCh is considered to be a weak Lewis acid, the involvement of a bismuth enolate is perhaps implicated. Enolate intermediates are definitely generated when tetraalkylammonium fluorides or tris(dialkylamino)sulfonium (TAS) difluorotrimethylsiliconates (104) are used as reagents to promote the reactions of enol silyl ethers. Their chemistry will therefore not be discussed in this chapter. 

Deviations from this general behavior are found with various alkyl aluminum alcoholates. Since alkoxy ions, OR, are stronger Lewis bases than the halogen ions, the Lewis acidity of the dialkylalkoxy alanes formed with the hypothetical Lewis acid R2A1+ (32) is low, i.e., there is little tendency to form complexes with weak bases. Accordingly, diethylaluminum alcoholate forms stable salts with potassium and cesium fluoride but not with sodium fluoride. The tendency to form complexes (e.g., with KF and NaH) increases in going from R2A10R to RAl(OR)2 (Fig. 9) (156, 322). Thus the... 

In similar fashion and in contrast to its isomerization by fluoride ion and other bases to perfluoropropionyl fluoride (6), HFPO is transformed by Lewis acids such as antimony pentafluoride ° or aluminum chlorofluoride into another isomer, hexafluoroacetone (20). 

The reaction of perfluorinated cyclic amines with strong Lewis acids, such as SbFs or aluminum chlorofluoride (ACF), at elevated temperature results in rapid cleavage of amine, leading to the formation of cyclic perfluorinated imidoyl fluorides (Fig. 9.23). In contrast to AICI3 reactions, this process is catalytic. The outcome of the reaction depends on the structure of amine. For example, the reaction of A-alkyl piperidines or morpholines leads to the elimination of perfluoroalkane... 

Alkylation of Aromatics. Aromatic hydrocarbons containing a replaceable hydrogen can be alkylated unless steric effects prevent introduction of the alkyl group (61,78-82). The reaction is called the Friedel-Crafts alkylation, first realized in the presence of aluminum chloride, which is the catalyst still the most frequently used and studied in Friedel-Crafts reactions. In addition, many other acid catalysts are effective (80,82-84). These include other Lewis acids (other aluminum halides, gallium chloride, boron trifluoride, ferric chloride, zinc chloride, stannous and stannic chloride, antimony chloride) and protic acids (hydrogen fluoride, concentrated sulfuric acid, phosphoric acid, polyphosphoric acid, trifluo-romethanesulfonic acid, and alkane- and arenesulfonic acids). 

Additions to Conjugated Systems. The reaction of TMSCF3 with a, 8-unsaturated aldehydes or ketones under fluoride activation affords almost exclusively the 1,2-addition products. " Moreover, the 1,4-addition pathway may also participate in some cases, and occurs predominantly in 2-perfluoroalkyl chromones and related systems (eq 22). A 1,6-addition process in a suitably substituted substrate has also been described. A more general method for the 1,4-addition of CF3 groups to different enones consisted in the prior complexa-tion of the carbonyl with a bulky Lewis acid [aluminum tris(2,6-diphenylphenoxide)]. ... 

However, before doing so, an alternative synthesis approach to an equally Lewis acidic aluminum fluoride phase that can be obtained by a very simple reaction as shown by Equation (6.7) will be briefly introduced, since both phases exhibit very similar catalytic properties ... 

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