Chapter 9.SE, Problem 36AP

Interpretation Introduction

a)

Interpretation:

How to convert an alkyne into an alkene, if necessary using more than one step, is to be shown.

Concept introduction:

Alkynes can be converted in to the corresponding alkenes by treating with H₂ in the presence of Pd-BaSO₄.

To show:

How to convert an alkyne into an alkene, if necessary using more than one step.

Answer to Problem 36AP

Alkynes can be reduced to the corresponding alkenes in a single step as shown.

Explanation of Solution

Alkynes when treated with H₂ in the presence of Pd-BaSO₄ add two equivalents of hydrogen to yield an alkane. In the presence of Pd-BaSO₄, the reduction stops in the alkene stage itself as only one equivalent of hydrogen is added by the alkynes.

Conclusion

Alkynes when treated with hydrogen in the presence of Pd-BaSO₄ get reduced to alkenes in a single step.

Interpretation Introduction

b)

Interpretation:

How to convert an alkyne into an alkane, if necessary using more than one step, is to be shown.

Concept introduction:

Alkynes add two equivalents of hydrogen when treated with H₂ in the presence of Raney nickel catalyst.

To show:

How to convert an alkyne into an alkane, if necessary using more than one step.

Answer to Problem 36AP

Alkynes can be reduced to the corresponding alkanes by using the step shown.

Explanation of Solution

Alkynes when treated with H₂ in the presence of Raney Ni add two equivalents of hydrogen to yield the corresponding alkane.

Conclusion

Alkynes can be reduced to the corresponding alkanes by using the step shown.

Interpretation Introduction

c)

Interpretation:

How to convert an alkyne into an aldehyde, if necessary using more than one step is to be shown.

Concept introduction:

Symmetrical internal alkynes yield an aldehyde as a single product during ozonolysis. The alkyne given can be converted in to a higher symmetrical alkyne by treating with NaNH₂ in NH3 and RCl. The symmetrical alkyne thus obtained upon ozonolysis followed by reduction with Zn and acetic acid give an aldehyde as the only product.

To state:

How to convert an alkyne into an aldehyde , if necessary using more than one step.

Answer to Problem 36AP

The terminal alkyne can be converted into an aldehyde through the steps shown.

Explanation of Solution

The alkyne is first converted in to a higher alkyne by treating it with NaNH₂ and then with RCl. The higher alkyne, being symmetrical, upon ozonolysis followed by reduction with Zn and acetic acid gets cleaved to give the aldehyde required as the product.

Conclusion

The terminal alkyne can be converted into an aldehyde through the steps shown.

Interpretation Introduction

d)

Interpretation:

How to convert an alkyne into secondary alkyl halide, if necessary using more than one step, is to be shown.

Concept introduction:

Terminal alkynes when reduced with H₂ in the presence of Pd-BaSO₄ catalyst yield the corresponding alkenes. The alkenes when treated with HCl yield an alkyl halide following Markovnikov regiochemistry.

To state:

How to convert an alkyne into a secondary alkyl halide, if necessary using more than one step.

Answer to Problem 36AP

The alkyne can be converted into a secondary alkyl halide through the steps shown.

Explanation of Solution

The alkyne is first converted in to an alkene by treating it with H₂ in the presence of Pd-BaSO₄catalyst. Addition of HCl to alkenes follows Markovnikov regiochemistry. The chlorine atom adds to the carbon with one substituent and H adds to the terminal carbon without substituents to yield the product required.

Conclusion

An alkyne can be converted into a secondary alkyl halide through the steps shown.

Interpretation Introduction

e)

Interpretation:

How to convert (if necessary using more than one step) an alkyne into a primary alcohol that contains one more carbon is to be shown.

Concept introduction:

Alkynes can be converted into a primary alcohol through the following steps. The alkyne is first reduced to an alkene using H₂ and Pd-BaSO₄. Hydrohalogenation converts the alkene in to an alkyl halide which when treated with NaOH yields the required alcohol.

To state:

How to convert an alkyne into a primary alcohol, if necessary using more than one step.

Answer to Problem 36AP

The alkyne can be converted in to the alcohol through the steps shown.

Explanation of Solution

The alkyne gets reduced to an alkene when treated with H₂ and Pd-BaSO₄. The alkene gets converted in to a primary alkyl halide when treated with HCl in the presence of a peroxide following anti Markovnikov regiochemistry. The alkyl halide yields the alcohol when the nucleophile OH- displaces Cl- when treated with NaOH.

Conclusion

The alkyne can be converted in to the alcohol through the steps shown.

Interpretation Introduction

f)

Interpretation:

How to convert an alkyne into its next higher alkyne, if necessary using more than one step, is to be shown.

Concept introduction:

Terminal alkynes are converted in to acetylides by treating with NaNH₂ in liquid ammonia. The acetylides can be converted to higher alkynes by treating with alkyl halides having required number of carbon atoms.

To state:

How to convert an alkyne into its next higher alkyne, if necessary using more than one step.

Answer to Problem 36AP

The alkyne can be converted in to its next higher alkyne through the steps shown.

Explanation of Solution

The alkyne, being acidic, when treated with NaNH₂ in liquid ammonia is converted in to the sodium acetylide. The acetylide upon treatment with methyl chloride yields the next higher alkyne.

Conclusion

The alkyne can be converted in to its next higher alkyne through the steps shown.

Interpretation Introduction

g)

Interpretation:

How to convert an alkyne into a ketone, if necessary using more than one step, is to be shown.

Concept introduction:

Terminal alkynes when hydrated in the presence of dilute H₂SO₄ in the presence of HgSO₄ are converted in to enols. The addition of water takes place following Markovnikov regiochemistry. The enols upon tautomerization yield ketones as the product.

To state:

How to convert an alkyne into a ketone, if necessary, using more than one step.

Answer to Problem 36AP

The alkyne can be converted in to a ketone using the step shown.

Explanation of Solution

Addition of water takes place to the triple bond when the alkyne is treated with dilute H₂SO₄ in the presence of HgSO₄ following Markovnikov regiochemistry. The OH adds on to the carbon with one substituent and H adds on to the terminal carbon with no substituent to yield an enol. The enol then undergoes tautomerization to give the ketone as the product.

Conclusion

The alkyne can be converted in to a ketone using the step shown.

Interpretation Introduction

h)

Interpretation:

How to convert an alkyne into an epoxide, if necessary using more than one step, is to be shown.

Concept introduction:

Terminal alkynes are converted in to alkenes by treating with H₂ in the presence of Pd-BaSO₄. The alkenes are converted in to epoxides by treating them with peracids like meta - chloroperoxybenzoic acid.

To state:

How to convert an alkyne into an epoxide, if necessary using more than one step.

Answer to Problem 36AP

The alkyne can be converted in to an epoxide using the steps shown.

RCO₃H=meta - chloroperoxybenzoic acid

Explanation of Solution

The terminal alkyne when reduced with H₂ in the presence of Pd-BaSO₄ yield the corresponding alkene. When the alkene is treated with meta -chloroperoxybenzoic acid, transfer of an oxygen atom from the acid to the double bond in alkene takes place with syn stereochemistry to yield the epoxide.

Conclusion

The alkyne can be converted in to the epoxide through the steps shown.

RCO₃H=meta - chloroperoxybenzoic acid.