The synthesis of 3 - octyne is achieved by adding a bromoalkane into a mixture of sodium amide and an alkyne. The bromoalkane and alkyne respectively are
A
BrCH2CH2CH2CH2CH3andCH3CH2C≡CH
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B
BrCH2CH2CH3andCH3CH2C≡CH
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C
BrCH2CH2CH2CH2CH3andCH3C≡CH
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D
BrCH2CH2CH2CH3andCH3CH2C≡CH
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Solution
The correct option is DBrCH2CH2CH2CH3andCH3CH2C≡CH Higher alkynes are prepared from terminal alkynes.
By treating terminal alkyne with sodium metal at high temperature or with sodamide (NaNH2) will result in the formation of its sodium salt.
The carbanion formed is a good nucleophile and can undergo nucleophilic substitution reactions with 1oor2o alkyl halides to produce an alkyne.
(a) CH3CH2C≡CH+Br−CH2CH2CH2CH2CH3→CH3CH2−C≡C−CH2CH23−nonyneCH2CH2CH3
(b) CH3CH2C≡CH+Br−CH2CH2CH3→CH3CH2C≡C−CH2CH2CH3
(c) CH3C≡CH+Br−CH2CH2CH2CH2CH3→CH3−C≡C−CH2CH22−octyneCH2CH2CH3
(d) CH3CH2C≡CH+Br−CH2CH2CH2CH3→CH3CH2−C≡C−CH2CH23−octyneCH2CH3
Thus, reactants of option (d) gives 3-Octyne.