Acylative cleavage of ethers

With regard to the mechanism of this reaction and the nature of the catalyst, the authors do not believe the graphite itself is the catalyst. In fact, diethyl and di-n-butyl ethers are inert toward benzoyl chloride in the presence of graphite B. It is also known that metal chlorides, especially FeCh [82], are catalysts for this reac- 

An equimolar (10 mmol) mixture of benzoyl chloride and n-butyl oxide adsorbed on 5 g graphite A was sequentially irradiated with 90 W incident power. The conversion reached 80% (Yield of isolated n-butyl benzoate (69) 62%). With ethyl oxide, the yield of ethyl benzoate (68) was lower, but noteworthy considering the volatility of this oxide, and the significant retentive power of graphite towards organic compounds. These preliminary results have not yet been expanded, but it is certain that more reactive ethers, like those substituted with sec- or teri-alkyl, benzylic or allylic groups, are deavable in the same way. 

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Scheme 5.1-15 The acylative cleavage of ethers in an ionic liquid.

Use of graphite-supported methodology has been reported for three types of reaction - the Friedel-Crafts acylation [15, 16, 27, 66], the acylative cleavage of ethers [15, 16], and the ketodecarboxylation of carboxylic diacids [67, 68], either with conventional heating (GS/A) or MW irradiation (GS/MW coupling) these are discussed below. First, however, we describe the analysis of two commercial graphites of different purity which are used for these experiments. 

Esterification reactions readily occur in ionic liquids. A simple example is the reaction of acetic, decanoic and octadecanoic acid with alcohols such as methanol, 1-butanol or 1-octanol. Here, Tang et al. used the ionic liquid [H-MIM][BF4] (this is a simple mixture of 1-methylimidazole and tetrafluoroboric acid) as a solvent and catalyst for the reaction [189]. Singer and coworkers have shown that benzoyl chloride reacts with ethers to give alkyl benzoates [190] in chloroaluminate(iii) ionic liquids. This reaction results in the acylative cleavage of ethers, and a number of reactions with cyclic and acyclic ethers were investigated in the ionic liquid [EMIMjl-AICI3 (X = 0.67). Two examples are shown in Scheme 5.2-79. 

Green, L., Hemeon, L, Singer, R.D. (2000). l-Ethyl-3-methylimidazolium halogenoaluminate ionic liquids as reaction media for the acylative cleavage of ethers. Tetrahedron Lett., 41, 9, (February 2000) 1343-1346, ISSN 0040-4039... 

B.2.2. Dialkyl Ether Cleavage. Varying the mole fraction of AICI3 in an ionic liquid can optimize reactions that are sensitive to the strength of Lewis acidity. When the ionic liquids [EMIM]C1/A1C13 were applied for the acylative cleavage of dialkyl ethers (Scheme 6), the reaction was found to be sensitive to the bulk Lewis acidity of the ionic liquid solvent 138). 

The acylative cleavage of the cyclic ether tetrahydrofuran showed an excellent yield (95%) to 4-iodobutylbenzoate when fully acidic ionic liquid [EMIM]Al2Cl7 was used, but the yield to di-functionalized product (61%) suffered when the mildly acidic halogenoaluminate ionic liquid (which has a mole fraction of AICI3 (x) at a value of 0.52) was used as the solvent. In contrast, for 1,5-dimethyltetrahydrofuran and tetrahydropyran, a good yield to the cleavage products was obtained when the mildly acidic chloroaluminate was used. 

Alcoholysis of trihalides 0-6 Hydrolysis of ortho esters 0-20 Alcoholysis of acyl halides 0-21 Alcoholysis of anhydrides 0-22 Esterification of carboxylic acids 0-23 Transesterification 0-24 Alkylation of carboxylic acid salts 0-25 Cleavage of ethers with anhydrides 0-26 Alkylation of carboxylic acids with diazo compounds... 

Cleavage of ethers Organoaluminum reagents, 202 Decarbonylation of acyl halides Tetrakis(triphenylphosphine)palla-dium(0), 289 Dehalogenation... 

Cleavage of ethers. A few reports have mentioned that acyl iodides can cleave ethers in the absence of a Lewis acid. Since acyl iodides are not readily available, Oku et al. have used Nal and an acyl chloride as a possible equivalent. In any case, the system does cleave both cyclic and acyclic ethers selectively at the less substituted a-C—O bond. Although any acyl chloride can be used, use of pivaloyl chloride is particularly attractive because the resulting pivaloyl esters are readily hydrolyzed. Indeed this system is particularly useful for deprotection of methyl ethers. 

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],... 

There are cases when a substrate is not used for growth, but is metabolized in the presence of a second substrate that is used to support microorganism reproduction. This type of transformation is called cometabolism. Cometabolic conversions that apparently involve a single enzyme include hydroxylations, oxidations, denitrations, deaminations, hydrolyses, acylations, and cleavages of ether bonds. Many of these conversions are complex and involve several enzymes. This may be explained by the existence of enzymes that perform a single type of reaction, but which act on a series of closely related molecules. 

Cleavage of Ethers. In aprotic, anhydrous solvents, BFs-MeOH is useful for the cleavage of trityl ethers at rt. Under these conditions, O- and Ai-acyl groups, 0-sulfonyl, W-alkoxycarbonyl, O-methyl, O-benzyl, and acetal groups are not cleaved. 

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