Chapter 18.SE, Problem 45AP

Interpretation Introduction

a)

Interpretation:

How to bring out the transformation given is to be shown.

Concept introduction:

Alkenes can be converted in to ethers by the alkoxymercuration-reduction process, in which an alcohol adds to the double bond in alkene following Markovnikov regiochemistry. The alkene is first treated with trifluoromercuric acetate. The organomercuric intermediate compound obtained when reduced with NaBH₄ yields the ether equired.

To show:

How to bring out the transformation given.

Answer to Problem 45AP

Cyclohexene can be transformed into cyclohexyl ethyl ether by subjecting cyclohexene to alkoxymercuration-reduction process.

Explanation of Solution

When cyclohexene is treated with trifluoromercuric acetate, a mercurinium ion is formed. The attack of ethanol on the mercurinium ion leads to the formation of an organomercuric compound. Subsequent treatment of the mercuric compound with NaBH4 breaks the C-Hg bond and yields the ether.

Conclusion

Cyclohexene can be transformed into cyclohexyl ethyl ether by subjecting cyclohexene to alkoxymercuration-reduction process.

Interpretation Introduction

b)

Interpretation:

How to bring out the transformation given is to be shown.

Concept introduction:

Ethers are cleaved by strong acids. The cleavage takes place either by S_N¹ or S_N² mechanisms, depending upon the structure of the substrate. Ethers with only primary and secondary alkyl groups react by S_N² mechanism. The Br- or I- attacks the protonated ether at the less hindered side to yield a single alcohol and a single alkyl halide. Ethers with a tertiary, benzylic or an allylic group cleave either by S_N¹ or E1 mechanism because these can produce a stable carbocations yielding alkenes and alcohols.

To give:

How to bring out the transformation given.

Answer to Problem 45AP

The transformation required can be brought about by treating the ether with HBr.

Explanation of Solution

The ether given has an oxygen atom attached to a primary and a secondary carbon. The protonation of the ethereal oxygen by the acid and the subsequent elimination of methanol by the attack of the bromide ion from the less hindered side through S_N² mechanism results in the formation of 1-bromo-4-methylcyclohexane with inversion of configuration (The methyl and methoxy groups are in the same faces in the reactant while the methyl and bromine are in the opposite faces in the product).

Conclusion

The transformation required can be brought about by treating the ether with HBr.

Interpretation Introduction

c)

Interpretation:

How to transform 4-tert-butylcyclohex-1-ene into 1,2-trans-4-tert-butylcyclohex-1,2-diol is to be shown.

Concept introduction:

Alkenes when treated with peracids yield epoxides. The epoxide ring can be opened by hydrolysis, in the presence of a base, to get the trans diol.

To give:

How to transform 4-tert-butylcyclohex-1-ene into 1,2-trans-4-tert-butylcyclohex-1,2-diol.

Answer to Problem 45AP

4-tert-butylcyclohex-1-ene can be converted into 1,2-trans-4-tert-butylcyclohex-1,2-diol by following the steps shown below.

Explanation of Solution

When 4-tert-butylcyclohex-1-ene is treated peracids like m-chloroperbenzoic acids, an oxygen atom is transformed to the double bond in alkene in a syn manner to produce an epoxide in a single step. The attack of the hydroxide ion on the epoxide leads to the formation of an anionic intermediate which the picks up a proton to yield the diol.

Conclusion

4-tert-butylcyclohex-1-ene can be converted into 1,2-trans-4-tert-butylcyclohex-1,2-diol by following the steps shown below.

Interpretation Introduction

d)

Interpretation:

How to transform 1-hexyne into n-hexyl methyl ether is to be shown.

Concept introduction:

An ether is to be prepared from an alkyne. For this the alkyne is first converted into an alkene by reduction with Lindlar catalyst. Hydroboration-oxidation of an alkene yields an alcohol. Treatment of alcohol with NaH yields its alkoxide which when treated with an alkyl halide gives the ether.

To show:

How to transform 1-hexyne into n-hexyl methyl ether.

Answer to Problem 45AP

1-hexyne can be converted into n-hexyl methyl ether by following the steps shown below.

Explanation of Solution

1-Hexyne when reduced with Lindler catalyst yields 1-hexene as the reduction will stop at the alkene stage. Hydroboration with BH₃ followed by oxidation with H₂O₂, OH- results in 1-hexanol by the addition of water, following anti-Markovnikov regiochemistry, to the double bond. The alcohol is converted into its alkoxide when treated with with NaH which then reacts with methyl iodide to yield n-hexyl methyl ether.

Conclusion

1-hexyne can be converted into n-hexyl methyl ether by following the steps shown below.

Interpretation Introduction

e)

Interpretation:

How to convert 1-hexyne into 2-methoxyhexane is to be shown.

Concept introduction:

An ether is to be prepared from an alkyne. The alkyne is first converted into an alkene by reduction with Lindlar catalyst. The alkene is subjected to alkoxymercuration and the product when reduced with NaBH₄ yields the ether required.

To show:

How to convert 1-hexyne into 2-methoxyhexane.

Answer to Problem 45AP

1-Hexyne can be converted into 2-methoxyhexane by following the steps shown below.

Explanation of Solution

1-Hexyne when reduced with Lindler catalyst yields 1-hexene as the reduction will stop at the alkene stage. Alkoxymercuration of 1-hexene with trifluoromercuric acetate and ethanol yields an intermediate organomercury compound which when reduced with NaBH₄ yields 2-methoxyhexane. The net result is the Markovnikov addition of methanol to the double bond in 1-hexene.

Conclusion

1-Hexyne can be converted into 2-methoxyhexane by following the steps shown below.