Acid-catalyzed alkene hydration

Relative Rates of Acid-Catalyzed Hydration of Some Representative Alkenes... 

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... 

Oxidation of tridecylborane gives 1 decanol The net result is the conversion of an alkene to an alcohol with a regioselectivity opposite to that of acid catalyzed hydration... 

Although 2 methylpropene undergoes acid catalyzed hydration m dilute sulfuric acid to form tert butyl alcohol (Section 6 10) a different reaction occurs m more concentrated solutions of sulfuric acid Rather than form the expected alkyl hydrogen sulfate (see Sec tion 6 9) 2 methylpropene is converted to a mixture of two isomeric C Hig alkenes... 

Acid catalyzed hydration of alkenes (Section 6 10) Water adds to the double bond in accordance with Markovnikov s rule... 

Epoxidation of an alkene followed by lithium aluminum hydride reduction of the result mg epoxide gives the same alcohol that would be obtained by acid catalyzed hydration (Section 610) of the alkene... 

This elimination reaction is the reverse of acid-catalyzed hydration, which was discussed in Section 6.2. Because a carbocation or closely related species is the intermediate, the elimination step would be expected to favor the more substituted alkene as discussed on p. 384. The El mechanism also explains the general trends in relative reactivity. Tertiary alcohols are the most reactive, and reactivity decreases going to secondary and primary alcohols. Also in accord with the El mechanism is the fact that rearranged products are found in cases where a carbocation intermediate would be expected to rearrange ... 

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. 

Oxymercuration/demercuration provides a milder alternative for the conventional acid-catalyzed hydration of alkenes. The reaction also provides the Markovnikov regiochemistry for unsymmetrical alkenes.33 Interestingly, an enantioselective/inverse phase-transfer catalysis (IPTC) reaction for the Markovnikov hydration of double bonds by an oxymercuration-demercuration reaction with cyclodextrins as catalysts was recently reported.34 Relative to the more common phase-transfer... 

The acid-catalyzed hydration of alkenes follows Markovnikov s rule => the reaction does not yield 1° alcohols except in the special case of the hydration of ethene. 

Because rearrangements often occur, the acid-catalyzed hydration of alkenes... 

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 results of studies of the acid-catalyzed hydration of oxygen-, sulfur-, seleno-and nitrogen-substituted alkenes and the relevance of this work to partitioning of the corresponding carbocation intermediates (Chart 1) between deprotonation and nucleophile addition was reviewed in 1986.70. We present here a brief summary of this earlier review, along with additional discussion of recent literature. 

Different rate-determining steps are observed for the acid-catalyzed hydration of vinyl ethers (alkene protonation, ks kp) and hydration of enamines (addition of solvent to an iminium ion intermediate, ks increasing stabilization of a-CH substituted carbocations by 71-electron donation from an adjacent electronegative atom results in a larger decrease in ks for nucleophile addition of solvent than in kp for deprotonation of the carbocation by solvent. 

Alkene and alkyne Bromination, acetic acid Chlorination, acetic acid Acid-catalyzed hydration, water... 

Other cations (Cu2+, Pd2+, Ru3+, Ni2+, Rh3+) incorporated into Nafion-H have been found to promote hydration.36 Other metals that catalyze hydration of alkynes include gold(III),37 ruthenium(in),38 and platinum(II) (Zeise s salt39 40 and halides40), p-Methoxybenzenetellurinic acid is very effective in the hydration of terminal alkynes 41 Similar to the hydration of alkenes, photochemical acid-catalyzed hydration of alkynes is possible ... 

The use of silica-supported Zn(BH4)2 is a useful procedure for the hydration of unactivated alkenes and alkynes.559 The main products are usually formed as a result of anti-Markovnikov addition. In contrast to acid-catalyzed hydration (see Section 6.1.2), this procedure allows the transformation of alkynes to alcohols. 

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