Ethers cleavage with sulfuric acid

Carboxylic acid anhydrides generally react with sulfur tetrafluoride in the same manner as carboxylic acids to give acid fluorides, then trifluoromethyl derivatives. Various cyclic anhydrides, which are particularly stable under acidic conditions, react without cleavage to give, in a stepwise fashion, difluoro lactones and a,a,a, a -tetrafluoro ethers. Conversely, the corresponding diacids are readily dehydrated by sulfur tetrafluoride to give anhydrides in the first step of the reaction. Therefore, in this section reactions of carboxylic acids and carboxylic acid anhydrides are discussed together. 

Aliphatic and cycloaliphatic monocarboxylic acids react with sulfur tetrafluoride to give, in general, 1,1,1-trifluoroalkanes as the main products together with considerable amounts of bis(l,1-difluoroalkyl) ethers. Yields of the ethers are related to the nature of the acid and to the reaction conditions. The optimum conditions for the formation of the ethers are dependent on the stability of the ethers towards protolytic cleavage in highly acidic reaction media and on the reactivity of the acids towards sulfur tetrafluoride. 

In contrast to linear unsaturated acids and anhydrides vide supra), 3,4,5,6-tetrahydrophthalic anhydride reacts with sulfur tetrafluoride to give mainly bicyclo products, lactone 31 and tetrafluoro ether 32, with the trifluoromethyl derivatives 33 and 34 as minor products. The ratio of products strongly depends on the reaction conditions at elevated temperature (> 150°C) cleavage of the C —O —C bond and dehydrogenation occur resulting in l,2-bis(tri-fluoromethyl)benzene (35) in high yield.252... 

Regioselective debenzylation can be achieved by treatment with Lewis acids such as ferric chloride and S11CI4 or under acetolysis conditions with acetic anhydride and sulfuric acid, and several examples are depicted in Scheme 2.3.9 Acetolysis results in cleavage of the most acid-sensitive benzyl group. In general, primary benzyl ethers can be selectively acetolysed in the presence of secondary benzyl ethers. The regioselectivity of the reaction can be explained as follows sulfuric acid protonates acetic anhydride followed by the formation of an acetyl ion and acetic acid. The acetyl ion reacts with the sterically most accessible oxygen which is at... 

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

The solution of aluminum trihydride used in this synthesis is prepared by the reaction of 100% sulfuric acid with lithium tetrahydridoaluminate(l —) in dry tetrahydrofuran.3 Under nitrogen flow, a stoichiometric amount of the sulfuric acid is added dropwise by syringe at 0° to a solution of lithium tetrahydridoaluminate(l —) in dry tetrahydrofuran. The apparatus used is just like that shown in Fig. 2, except that an ice bath is used to cool the reaction flask and thus prevent ether cleavage. As the sulfuric acid is added to the lithium tetrahydridoaluminate(l —), a precipitate of lithium sulfate forms and hydrogen is evolved. For this reason, the reaction must be carried out in a hood. After all the sulfuric acid has been added, the resulting slurry is stirred for 2 hr, then filtered in a glove box.4,5 The filtrate, a clear solution of aluminum trihydride in tetrahydrofuran, is stored in the refrigerator at -20° until it is needed. 

The main applications of oxidation with chromium trioxide are transformations of primary alcohols into aldehydes [184, 537, 538, 543, 570, 571, 572, 573] or, rarely, into carboxylic acids [184, 574], and of secondary alcohols into ketones [406, 536, 542, 543, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584]. Jones reagent is especially successful for such oxidations. It is prepared by diluting with water a solution of 267 g of chromium trioxide in a mixture of 230 mL of concentrated sulfuric acid and 400 mL of water to 1 L to form an 8 N CrOj solution [565, 572, 579, 581, 585, 556]. Other oxidations with chromic oxide include the cleavage of carbon-carbon bonds to give carbonyl compounds or carboxylic acids [482, 566, 567, 569, 580, 587, 555], the conversion of sulfides into sulfoxides [541] and sulfones [559], and the transformation of alkyl silyl ethers into ketones or carboxylic acids [590]. 

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