Acid-catalyzed addition, of alcohols

Acid catalyzed addition of alcohols to alkenes is sometimes used Indeed before Its use as a gasoline additive was curtailed billions of pounds of tert butyl methyl ether (MTBE) was prepared by the reaction... 

Citral readily forms acetals by acid-catalyzed addition of alcohols or by the use of trialkoxyorthoformates. Citral dimethyl acetal [7549-37-3] is stable under alkaline conditions, whereas citral is not. Neryl and geranyl nitriles can be made by oximation of citral and dehydration of the intermediate oxime. For instance, geranonitrile [31983-27-4] is made as follows ... 

Usually, 3- and 4-substituted thianes are prepared from the 3- and 4-oxothians by the common techniques applicable to alicyclic chemistry. Reduction affords alcohols which may be etherified or halogenated, while oximation and reduction produces the amino derivatives, which are also accessible via the halo compounds. 2-Alkoxy and 2-alkylthio compounds are made by acid catalyzed addition of alcohols and thiols to 3,4-dihydro-2H-thiopyran (75MI22502) in a reaction analogous to the use of dihydropyran for protection of alcohols as THP ethers. 

Exercise 15-39 Write the mechanistic steps involved in the acid-catalyzed addition of alcohols to the cyclic ether 16. Why does cyclohexene react far less readily than 16 with alcohols under acidic conditions Write equations for the steps involved in the hydrolysis of 17 with aqueous acid. 

Alkyl ethers are generally prepared by acid-catalyzed addition of alcohols to an alkene or by Williamson ether synthesis (Scheme 1.18). 

Aldehydes and ketones undergo acid-catalyzed addition of water to form hydrates. Electron donation and bulky substituents decrease the percentage of hydrate present at equilibrium. Most hydrates are too unstable to be isolated. Acid-catalyzed addition of alcohol to aldehydes forms hemiacetals and acetals, and to ketones forms hemiketals... 

Lewis Acid Catalyzed Additions of Alcohols to Alkenes... 

Acid-Catalyzed Addition of Alcohols to Alkenes (Section 11.4C) Proton transfer to the alkene generates a carbocation. Nucleophilic addition of an alcohol to the car-bocation followed by proton transfer to the solvent gives the ether. 

As shown in Table 8.1, the preparation of some alcohols (with one or more hydroxyl [-OH] groups) has been provided earlier. Table 8.2 reminds the reader that (a) enols are in equilibrium with their corresponding carbonyl tautomers (Chapter 5) (b) acid-catalyzed addition of alcohols (R-OH R H) and thiols (R-SH R H) to, for example, alkenes can be used to produce ethers (R-O-R R, R H) and thioethers (R-S-R R, R H), respectively (Chapter 6) (c) ethers are readily formed by nucleophilic substitution of halogen (X = Cl, Br, I) by alkoxide (RO ) (Chapter 7) under the appropriate (SnI or Sn2) conditions and (d) substitution of a halogen on an aromatic ring (Ar-X, X = Cl, Br) can be effected by fusion with molten alkali (e.g., NaOH) (Chapter 7). 

An alternative method of masking the hydroxyl group of alcohols involves acetal formation by a nonaqueous acid-catalyzed addition of alcohol to the carbon-carbon double bond of 3-oxacyclohexene (dihydropyran) (Table 8.6, item 20).The product, an acetal, will also undergo acid-catalyzed hydrolysis, regenerating the alcohol and the hydrate of 3-oxacyclohexene (dihydropyran), 2-hydroxyoxacyclohexane (the cyclic form of 5-hydroxypentanal), as shown in Scheme 8.60. 

Many of the most interesting and useful reactions of aldehydes and ketones involve transformation of the initial product of nucleophilic addition to some other substance under the reaction conditions. An example is the acid-catalyzed addition of alcohols to aldehydes.The expected product, a hemiacetal, is not usually isolable, but reacts with an additional mole of the alcohol to give an acetal. 

Acid-Catalyzed Addition of Alcohols—Acetals (Sections 17-7 and 17-8)... 

Azirines react with alcohols in the presence of alkoxides to give alkoxyaziridines (67JA4456). Further treatment with alcohol and alkoxide results in the formation of amino ketone acetals. Alkoxyaziridines are not isolated in general from the acid-catalyzed addition of methanol to azirines. Azirines are also known to react with amines (66JOC1423). Frequently the initially produced adducts undergo subsequent transformations. 

The preparation of neopentyl alcohol from diisobutylene herein described represents an example of acid-catalyzed addition of hydrogen peroxide to a branched olefin, followed by an acid-catalyzed rearrangement of the tertiary hydroperoxide formed. In addition to neopentyl alcohol, there are formed acetone and also small amounts of methanol and methyl neopentyl ketone by an alternative rearrangement of the hydroperoxide. 

The formation of alcohols by acid-catalyzed addition of water to alkenes is a fundamental organic reaction. At the most rudimentary mechanistic level, it can be viewed as involving a carbocation intermediate. The alkene is protonated, and the carbocation is then captured by water. 

The acid-catalyzed addition of an aldehyde—often formaldehyde 1—to a carbon-carbon double bond can lead to formation of a variety of products. Depending on substrate structure and reaction conditions, a 1,3-diol 3, allylic alcohol 4 or a 1,3-dioxane 5 may be formed. This so-called Prins reaction often leads to a mixture of products. 

A Alkenes can be converted into alcohols by acid-catalyzed addition of water. Assuming that Vlarkovnikov s rule is valid, predict the major alcohol product from each of the following alkenes. 

Most of the biochemical reactions that take place in the body, as well as many organic reactions in the laboratory, yield products with chirality centers. Fo example, acid-catalyzed addition of H2O to 1-butene in the laboratory yield 2-butanol, a chiral alcohol. What is the stereochemistry of this chiral product If a single enantiomer is formed, is it R or 5 If a mixture of enantiomers i formed, how much of each In fact, the 2-butanol produced is a racemic mix ture of R and S enantiomers. Let s see why. 

The acid-catalyzed addition of water to the double bond of an alkene is a method for the preparation of low molecular weight alcohols that has its greatest utility in large-scale industrial processes. 

The fourth reaction is transformation of the aldehyde into an acetal. This proceeds by acid-catalyzed addition of an alcohol to the carbonyl, loss of H2O, and then addition of the acid O to the carbocation. Other perfectly correct sequences of steps could be written here. 

This protective group is introduced by an acid-catalyzed addition of the alcohol to the vinyl ether moiety in dihydropyran. />-Toluenesulfonic acid or its pyridinium salt is used most frequently as the catalyst,3 although other catalysts are advantageous in special cases. The THP group can be removed by dilute aqueous acid. The chemistry involved in both the introduction and deprotection stages is the reversible acid-catalyzed formation and hydrolysis of an acetal (see Part A, Section 8.1). 

In a clever adaptation of the acid-catalyzed addition of />-quinone ketals to olefins Buchi and Chu condensed 586 with 1,2-dimethylcyclopentene in the presents of stannic chloride and inun ately reduce the two diastereomeric adducts with sodium borohydride The major alcohol 587 was separated, catalytically hydrogenated, and converted to the tetrahydropyranyl derivative 588 (Scheme XLVII). 

The chemistry of 1,3-dioxins containing four double bonds is poorly developed. A few examples of nucleophilic additions have been demonstrated. The proton-catalyzed addition of alcohol or carboxylic acid nucleophiles to anhydro derivatives of acetylsalicylic acid - new prodrugs of aspirin - was reported to give the C-2 O-substituted 1,3-dioxanes in 41-60% yield (Equation 19) <2001TL5231, 2003CRC265>. 

Acid-catalyzed addition of water and alcohols to 4/f-chromenes gives the expected products as predicted by Markovnikov s rule (56JCS4785) an anti-Markovnikov addition of methanol followed by the reintroduction of a double bond in the alternative position gives an overall effect of substitution of hydrogen by methoxy and this is effected by treating methyl 2if-chromene-3-carboxylate (166) with triphenylmethyl perchlorate and addition of methanol to the resulting benzopyrylium salt (167) (72CR(C)(274)650). 

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