Ethers by acids

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

A -3-Ketones readily form A -dien-3-ol ethers by acid-catalyzed reaction with orthoformates. Under these conditions A" -3-ketones can be selectively protected in the presence of 17- and 20-ketones (72) (73)]. 

Preparation of ethers by acid dehydration of secondary or tertiaiy alcohols is not a suitable method. Give reason. 

The thermal rearrangement of allyl ethers is a process entirely different from. the rearrangement of saturated alkyl phenyl ethers by acidic catalysts.103 The latter process seems to be intermolecular, gives consider-... 

Protection of alcohols. Primary and secondary alcohols are converted into the 2-tetrahydrothienyl (THT) ethers by acid-catalyzed exchange with 1. The ethers can be cleaved quantitatively by HgCU in aqueous acetonitrile in fact the THT group is cleaved faster than the methylthiomethyl group (6, 302). 

We have already discussed the cleavage of ethers by acids (Sec. 17.7). Cleavage of methyl aryl ethers by concentrated hydriodic acid is the basis of an important analytical procedure (the Zeisel procedure See. 17.16). 

Stereoselective syntheses of substituted cyclic ethers by acid-catalyzed cyclization of vinylsilanes bearing an hydroxy group 03SL143. 

Example Formation of an ether by acid catalyzed dimerisation of an alcohol. Response surface model from a 3 factorial design. [3]... 

The formations of an ether by acid catalyzed dimerisation of an alcohol was studied. 

Catalytic hydrogenolysis of trimethylsilyl enol ethers by acidic ruthenium dihydrogen complexes... 

CATALYTIC HYDROGENOLYSIS OF TRIMETHYLSILYL ENOL ETHERS BY ACIDIC RUTHENIUM DIHYDROGEN COMPLEXES... 

The cleavage of the ether by acid involves nucleophilic attack by halide ion on the protonated ether. This causes displacement of the weakly basic alcohol molecule as illustrated ... 

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