Hydration of an alkene

You may have noticed that the acid catalyzed hydration of an alkene and the acid catalyzed dehydration of an alcohol are the reverse of each other... 

Acid catalyzed hydration converts alkenes to alcohols with regioselectivity according to Markovnikov s rule Frequently however one needs an alcohol having a structure that corresponds to hydration of an alkene with a regioselectivity opposite to that of Markovnikov s rule The conversion of 1 decene to 1 decanol is an example of such a transformation... 

The combination of hydroboration and oxidation leads to the overall hydration of an alkene. Notice, however, that water is not a reactant. The hydrogen that becomes bonded to carbon comes from the organoborane, and the hydroxyl group from hydrogen peroxide. 

Mechanism of the acid-catalyzed hydration of an alkene to yield an alcohol. Protonation of the alkene gives a carbocation intermediate that reacts with water. 

Hydration of an alkene—the addition of water—is carried out by either of two procedures, depending on the product desired. Oxymercuration involves electrophilic addition of Hg2+ to an alkene, followed by trapping of the cation intermediate with water and subsequent treatment with NaBH4. Hydroboration involves addition of borane (BH3) followed by oxidation of the intermediate organoborane with alkaline H202- The two hydration methods are complementary oxymercuration gives the product of Markovnikov addition, whereas hydroboration/oxidation gives the product with non-Markovnikov syn stereochemistry. 

The hydration of an alkene double bond under strongly acidic conditions is again a classical reaction that involves a carbocation intermediate, which often leads to various competing reaction products.27 The regiochemistry of the water addition follows the Markovnikov rule.28... 

Thus the rate of hydration of an alkene, directly with water,... 

Acid-catalysed hydration of an alkene is the reversal of the similarly acid-catalysed dehydration (by the El pathway, cf. p. 248) of alcohols to alkenes ... 

The hydration of an alkene is best carried out using dilute acid so that the concentration of water is high. 

Fig. 2 Free energy reaction coordinate profiles for the stepwise acid-catalyzed hydration of an alkene through a carbocation intermediate (Scheme 5). (a) Reaction profile for the case where alkene protonation is rate determining (ks kp). This profile shows a change in rate-determining step as a result of Bronsted catalysis of protonation of the alkene. (b) Reaction profile for the case where addition of solvent to the carbocation is rate determining (ks fcp). This profile shows a change in rate-determining step as a result of trapping of the carbocation by an added nucleophilic reagent.

The general reaction for the catalytic hydration of an alkene to produce an alcohol is shown in Figure 3-6, and the mechanism is in Figure 3 7. This process is an excimple of a Markovnikov addition (as seen in Organic Chemistry 1). 

Hydration of an alkene also follows Markovnikov s rule. Hydration takes place when water is added to an alkene in the presence of an acid. Tlxis reaction is the reverse of dehydration of an alcohol. Low temperatures and dilute add drive this reaction toward alcohol formation high temperatures and concentrated acid drive the reaction toward alkene formation. 

We ve already looked at several alcohol synthesis reactions hydration of an alkene, oxymeixruration/demeicu ration, hydroboration, and nucleophilic substitution. 

B is correct. This is hydration of an alkene and follows Markovnikov s rule. 

Dimethyl-1-propanol cannot be prepared by hydration of an alkene, because no alkene can have this carbon skeleton. 

Although this reaction involves two steps, they can be run sequentially in the same flask. This procedure is usually the preferred method for the hydration of an alkene because the yields are higher than the acid-catalyzed addition described in Section 11.3, and rearrangements do not occur. 

Mechanism of the hydration of an alkene using mercuric acetate. 

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.)... 

Overall, this mechanism is similar to that for the hydration of an alkene (described in Section 11.3). o A proton adds to the double bond of dihydropyran. 

Mechanism 8-4 Acid-Catalyzed Hydration of an Alkene 338 8-5 Hydration by Oxymercuration-Demercuration 340 Mechanism 8-5 Oxymercuration of an Alkene 340 8-6 Alkoxymercuration-Demercuration 342 8-7 Hydroboration of Alkenes 343... 

An alkene may react with water in the presence of a strongly acidic catalyst to form an alcohol. Formally, this reaction is a hydration (the addition of water), with a hydrogen atom adding to one carbon and a hydroxyl group adding to the other. Hydration of an alkene is the reverse of the dehydration of alcohols we studied in Section 7-10. 

For dehydrating alcohols, a concentrated dehydrating acid (such as H2SO4 or H3PO4) is used to drive the equilibrium to favor the alkene. Hydration of an alkene, on the other hand, is accomplished by adding excess water to drive the equilibrium toward the alcohol. 

This hydration of an alkene by hydroboration-oxidation is another example of a reaction that does not follow the original statement of Markovnikov s rule (the product is anti-Markovnikov), but still follows our understanding of the reasoning behind Markovnikov s rule. The electrophilic boron atom adds to the less substituted end of the double bond, placing the positive charge (and the hydrogen atom) at the more substituted end. 

The addition of water to a molecule. Hydration of an alkene forms an alcohol, (p. 337)... 

CHAPTER 8 Ionic Addition of HX to an Alkene 332 Free-Radical Addition of HBr to Alkenes 334 Acid-Catalyzed Hydration of an Alkene 338 Oxymercuration of an Alkene 340 Hydroboration of an Alkene 345 Addition of Halogens to Alkenes 350 Formation of Halohydrins 352 Epoxidation of Alkenes 360 Acid-Catalyzed Opening of Epoxides 362 Olefin Metathesis 376... 

For synthesis of an alcohol, acid-catalyzed hydration of an alkene is useful in all of the following instances except ... 

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