Alkyl-aryl ethers, preparation

The reaction between an alkoxide ion and an aryl halide can be used to prepare alkyl aryl ethers only when the aryl halide is one that reacts rapidly by the addition-elim mation mechanism of nucleophilic aromatic substitution (Section 23 6)... 

Section 24.11 Phenoxide anions are nucleophilic toward alkyl halides, and the preparation of alkyl aryl ethers is easily achieved under Sn2 conditions. 

Cleavage conditions for alkyl benzyl ethers prepared from acid-labile benzyl alcohols are similar to those for the corresponding benzyl esters (Table 3.30). Aryl benzyl ethers, however, are generally cleaved more easily by acidolysis than esters or alkyl ethers. Phenols etherified with hydroxymethyl polystyrene, for instance, can even be released by treatment with TFA (Entry 1, Table 3.31). It has also been shown that Wang resin derived phenyl ethers are less stable than Wang resin derived esters towards refluxing acetic acid [29]. Alternatively, boron tribromide may be used to cleave aryl ethers from hydroxymethyl polystyrene [573],... 

Table 7.11. Preparation of alkyl aryl ethers from support-bound phenols.

Alternatively, alkyl aryl ethers can be prepared from support-bound aliphatic alcohols by Mitsunobu etherification with phenols (Table 7.13). In this variant of the Mit-sunobu reaction, the presence of residual methanol or ethanol is less critical than in the etherification of support-bound phenols, because no dialkyl ethers can be generated by the Mitsunobu reaction. For this reason, good results will also be obtained if the reaction mixture is allowed to warm upon mixing DEAD and the phosphine. Both triphenyl- and tributylphosphine can be used as the phosphine component. Tributyl-phosphine is a liquid and generally does not give rise to insoluble precipitates. This reagent must, however, be handled with care because it readily ignites in air when absorbed on paper. 

The condensation of tellurium tetrachloride with aromatic compounds was one of the first methods for the preparation of aryl tellurium trichlorides. Alkyl aryl ethers react easily with tellurium tetrachloride in refluxing chloroform or carbon tetrachloride (Vol. IX, p. 1153). The trichlorotelluro group enters in the /wa-position to the alkoxy group. Several additional monosubstituted benzenes and substituted phenols were found to condense with tellurium tetrachloride (Table 7, p. 306). 

The cleavage of alkyl aryl ethers is more important as a preparative method for phenols than for alkyl halides (method 97). The procedure has been employed as the final step in a synthesis proposed as a means for increasing the carbon chain of an alkyl halide, viz., ... 

Aluminum and boron halides are sometimes used to dealkylate alkyl aryl ethers to phenols. Boron tribromide cleaves aliphatic ethers to alcohols and alkyl halides, but the reaction has no preparative value in the aliphatic series. Aluminum halide and the ether first form a complex from which a molecule of alkyl halide is eliminated upon heating. 

The reaction has been successfully employed to prepare fluorophe-nols and hydroxybenzophenones. Diaryl ethers and alkyl aryl ethers are also cleaved by sodium amide, sodium hydroxide, and by... 

Of the alkylation systems described in Section 1.1.2.5.1, the DEAD-PhsP procedure cannot be used in the preparation of acyclic dialkyl ethers, but alkyl aryl ethers and cyclic ethers have been synthesized. The PhaP-CCU system is also effective for the cyclodehydration of 1,4- and 1,2-diols to tetrahydrofurans and epoxides, respectively. ... 

Preparation of alkyl aryl ethers by loss of water between a phenol and an alcohol is generally of little importance. It may, however, be noted that phloro-glucinol can be converted into di- or tri-alkyl ethers by means of hydrochloric acid 679 also some naphthols, anthracenols, and phenanthrols,680 e.g., oc- and... 

When an excess of the acid is applied, symmetrical alkyl ethers give the corresponding alkyl sulfonate as sole product, since the alcohol formed as intermediate is rapidly esterified this reaction is thus to be recommended for the preparation of alkyl sulfonates, though it should be noted that the water formed slows down the process the aryl-oxygen bond of alkyl aryl ethers is not broken, these compounds giving the alkyl sulfonate and the corresponding phenol. 

Alkyl aryl ethers. Two laboratories have reported independently that alkyl aryl ethers can be prepared by reaction of an alcohol and a phenol with this combination of reagents. The reaction proceeds with inversion in the case of 3j3-cholestanol (but not cholesterol). The reaction proceeds at room temperature inTHF. 

Table 1 shows the experimental conditions for the synthesis of azocellulose polymers through alkyl aryl ether formation via Mitsunobu reaction (Scheme 1). Samples AZOEST21 and AZOEST49 were prepared from ESTERCELL cellulose, and Sample AZOVIS69 was prepared from VISCOCELL cellulose. The degrees of substitution (DS) for these samples are 0.21, 0.49 and 0.69, respectively. 

Purpose. The conditions under which ethers are prepared are explored by the weU-known V lliamson ether synthesis.You will prepare alkyl aryl ethers by Sn2 reactions of alkyl halides with substituted phenoxide anions. The use of phase-transfer catalysis is demonstrated. 

The compounds whose preparations are described in Experiments [Ilk], [22B], [22C], and [22D] are alkyl aryl ethers. The general method of preparation is the Williamson synthesis, an Sn2 reaction spedficaUy between a phe-noxide ion (ArO ) nucleophile and an aUcyl halide. This reaction is often used for the synthesis of symmetrical and unsymmetrical ethers where at least one of the ether carbon atoms is primary or methyl, and thus amenable to an Sn2 reaction. Elimination (E2) is generally observed if secondary or tertiary halides are used, since phenoxide ions are also bases. 

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