Alcohols acid-catalyzed addition

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 ... 

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. 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

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). 

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). 

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. 

Addition of Water Alkenes don t react with pure water, but in the presence of a strong acid catalyst such as sulfuric acid, a hydration reaction takes place to yield an alcohol. An -H from water adds to one carbon, and an -OH adds to the other. For example, nearly 300 million gallons of ethyl alcohol (ethanol) are produced each year in the United States by the acid-catalyzed addition of water to ethylene ... 

These reactions are carried out in the presence of acidic and basic catalysts. The acid-catalyzed addition of ethyl alcohol to acetylene or to a vinyl ether produces acetals (diethers of 1,1-dihydroxyethane). The acid-catalyzed reaction of ethyl alcohol with an aldehyde or ketone also gives acetals. 

Hoffmann and Pete [106] have irradiated D-alk- 3 -e n y I salicylates and obtained products which result from rearrangement reactions of primary ortho adducts (Scheme 31). The authors realized that the linear tricyclic dienes, formed by ring closure of the cyclooctatriene derivatives, are enol ethers which can be converted into acetals by acid-catalyzed addition of an alcohol. This shifts the... 

Methyl-tertiary-butyl ether (MTBE) is one of the leading chemicals currently being made from isobutylene (methyl propene) via the acid-catalyzed addition of methyl alcohol. MTBE has been added to gasoline as a required oxygenate. Eiowever, it is under attack as a groundwater contaminant and is being phased out. 

Some additional examples are provided by the following equations. Note the excellent yields in all of the examples. Also note that the last example proceeds without rearrangement because the intermediate is a mercurinium ion rather than a carbocation. Attempts to prepare this alcohol by acid-catalyzed addition of water result in completely rearranged product. 

The mechanism of the formation of the tetrahydropyranyl ether (see Figure 23.1) is an acid-catalyzed addition of the alcohol to the double bond of the dihydropyran and is quite similar to the acid-catalyzed hydration of an alkene described in Section 11.3. Dihydropyran is especially reactive toward such an addition because the oxygen helps stabilize the carbocation that is initially produced in the reaction. The tetrahydropyranyl ether is inert toward bases and nucleophiles and serves to protect the alcohol from reagents with these properties. Although normal ethers are difficult to cleave, a tetrahydropyranyl ether is actually an acetal, and as such, it is readily cleaved under acidic conditions. (The mechanism for this cleavage is the reverse of that for acetal formation, shown in Figure 18.5 on page 776.)... 

Mercuric Ion-Catalyzed Hydration Alkynes undergo acid-catalyzed addition of water across the triple bond in the presence of mercuric ion as a catalyst. A mixture of mercuric sulfate in aqueous sulfuric acid is commonly used as the reagent. The hydration of alkynes is similar to the hydration of alkenes, and it also goes with Markovnikov orientation. The products are not the alcohols we might expect, however. 

The mechanism for this reaction is shown in Key Mechanism 18-6. The first step is a typical acid-catalyzed addition to the carbonyl group. The acid catalyst protonates the carbonyl group, and the alcohol (a weak nucleophile) attacks the protonated, activated... 

The first half is an acid-catalyzed addition of the alcohol to the carbonyl group. 

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