Chapter 18.SE, Problem 24MP

Interpretation Introduction

a)

Interpretation:

The products formed and the mechanism by which they are formed when tert-butyl ethyl ether is treated with HBr is to be given.

Concept introduction:

Ethers are cleaved by strong acids. The cleavage takes place either by SN¹ or SN² mechanisms, depending upon the structure of the substrate. Ethers with only primary and secondary alkyl groups react by SN² 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 SN¹ or E1 mechanism because these can produce a stable carbocations yielding alkenes and alcohols.

To give:

The products formed and the mechanism by which they are formed when tert-butyl ethyl ether is treated with HBr is to be given.

Answer to Problem 24MP

The products formed when tert-butyl ethyl ether is treated with HBr are ethanol and tert-butylbromide.

The mechanism by which they are formed is given below.

Explanation of Solution

The reaction occurs following SN¹ mechanism. The acid protonates the ether initially and the protonated ether eliminates ethanol to produce a stable tert-butyl carbocation. In the next step the bromide ion attacks the carbocation to yield tert-butyl bromide as the product.

Conclusion

The products formed when tert-butyl ethyl ether is treated with HBr are ethanol and tert-butylbromide.

The mechanism by which they are formed is given below.

Interpretation Introduction

b)

Interpretation:

The products formed and the mechanism by which they are formed when tert-butyl phenyl ether is treated with HBr is to be given.

Concept introduction:

Ethers are cleaved by strong acids. The cleavage takes place either by SN¹ or SN² mechanisms, depending upon the structure of the substrate. Ethers with only primary and secondary alkyl groups react by SN² 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 SN¹ or E1 mechanism because these can produce a stable carbocations yielding alkenes and alcohols.

To give:

The products formed and the mechanism by which they are formed when tert-butyl phenyl ether is treated with HBr.

Answer to Problem 24MP

The products formed when tert-butyl phenyl ether is treated with HBr are phenol and tert-butyl bromide.

The mechanism by which they are formed is given below.

Explanation of Solution

The reaction occurs following SN¹ mechanism. The acid protonates the ether initially and the protonated ether eliminates phenol to produce a stable tert-butyl carbocation. In the next step the bromide ion attacks the carbocation to yield tert-butyl bromide.

Conclusion

The products formed when tert-butyl phenyl ether is treated with HBr are phenol and tert-butyl bromide.

The mechanism by which they are formed is given below.

Interpretation Introduction

c)

Interpretation:

The products formed and the mechanism by which they are formed when tert-butyl isopropyl ether is treated with HI is to be given.

Concept introduction:

Ethers are cleaved by strong acids. The cleavage takes place either by SN¹ or SN² mechanisms, depending upon the structure of the substrate. Ethers with only primary and secondary alkyl groups react by SN² 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 SN¹ or E1 mechanism because these can produce a stable carbocations yielding alkenes and alcohols.

To give:

The products formed and the mechanism by which they are formed when tert-butyl isopropyl ether is treated with HI.

Answer to Problem 24MP

The products formed when tert-butyl isopropyl ether is treated with HI are tert-butyl bromide and 2-propanol.

The mechanism by which they are formed is given below.

Explanation of Solution

The reaction occurs following SN¹ mechanism. The acid protonates the ether initially and the protonated ether eliminates 2-propanol to produce a stable ^tert-butyl carbocation. In the next step the iodide ion attacks the carbocation to yield ^tert-butyl iodide.

Conclusion

The products formed when tert-butyl isopropyl ether is treated with HI are tert-butyl bromide and 2-propanol.

The mechanism by which they are formed is given below.

Interpretation Introduction

d)

Interpretation:

The products formed and the mechanism by which they are formed when ethyl 1-methylcyclohexyl ether is treated with HI is to be given.

Concept introduction:

Ethers are cleaved by strong acids. The cleavage takes place either by SN¹ or SN² mechanisms, depending upon the structure of the substrate. Ethers with only primary and secondary alkyl groups react by SN² 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 SN¹ or E1 mechanism because these can produce a stable carbocations yielding alkenes and alcohols.

To give:

The products formed and the mechanism by which they are formed when ethyl 1-methylcyclohexyl ether is treated with HI.

Answer to Problem 24MP

The products formed when ethyl 1-methylcyclohexyl ether is treated with HI are 1-iodo-1-methylcyclohexane and ethanol.

The mechanism by which they are formed is given below.

Explanation of Solution

The reaction occurs following SN1 mechanism. The acid protonates the ether initially and the protonated ether eliminates ethanol to produce a stable tert-butyl carbocation. In the next step the iodide ion attacks the carbocation to yield tert-butyl iodide.

Conclusion

The products formed when ethyl 1-methylcyclohexyl ether is treated with HI are 1-iodo-1-methylcyclohexane and ethanol.

The mechanism by which they are formed is given below.

All the reactions (a), (b), (c) and (d) occur through SN1 mechanism.

All the reactions, (a), (b), (c) and (d) take place following SN¹ mechanism. The protonated epoxide first loses an alcohol to yield a stable tert-butyl carbocation which is then attacked by the halide ion.