Q32E - Organic Chemistry (Mcmurry)

Question

Predict the products from reaction of 5-decyne with the following

reagents:

(a) ${\mathbf{H}}_{\mathbf{2}}$, Lindlar catalyst

(b) Li in ${\mathbf{NH}}_{\mathbf{3}}$ 

(c) 1 equiv ${\mathbf{Br}}_{\mathbf{2}}$

d) ${\mathbf{BH}}_{\mathbf{3}}$ in THF, then ${\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{2}}$,$\mathbf{OH}$

(e) ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$, ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$, ${\mathbf{HgSO}}_{\mathbf{4}}$

(f) Excess ${\mathbf{\text{H}}}_{\mathbf{2}}$, Pd/C catalyst

Step-by-Step Solution

Answer

(a) 

(b) 

(c) 

(d) 

(e) 

(f) 

Step 1: Reaction of alkyne with hydrogen and Lindlar’s catalyst

Alkynes are reduced to alkanes when they undergo reaction with hydrogen over a metal catalyst. The hydrogenation can be stopped with alkenes if Lindlar’s catalyst functions as the reagent.

Step 2: Reaction of 5-decyne with hydrogen and Lindlar’s catalyst

(a)The reaction of 5-decyne with ${\text{H}}_{\text{2}}$ and Lindlar’s catalyst produces (Z)-dex-5-ene as the product. The reaction can be given as:

Step 3: Reaction of alkyne with Li in NH 3

Alkynes can be converted to alkenes by using lithium in ammonia as the reagent. The alkene obtained in this reaction is a trans alkene.

Step 4: Reaction of 5-decyne with Li in NH 3

(b)The reaction of 5-decyne with Li in ammonia produces (E)-dec-5-ene as the product. The reaction can be given as:

Step 5: Reaction of alkyne with 1 equivalent of bromine

The reaction of an alkyne with one equivalent of bromine results in a dihaloalkene. These reactions are termed addition reactions.

Step 6: Reaction of 5-decyne with 1 equivalent of Br 2

(c)The reaction of 5-decyne with 1 equivalent of produces (E)-5,6-dibromodec-5-ene as the product. The reaction can be given as:

Step 7: Reaction of alkyne with BH 3 , THF, H 2 O 2 and OH -

Alkynes react with ${\mathbf{BH}}_{\mathbf{3}}$and THF to produce a vinylic borane. This reacts with ${\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{2}}$ and ${}^{\mathbf{-}}\mathbf{OH}$ to yield an enol that further gets converted to a ketone.

Step 8: Reaction of 5-decyne with BH 3 , THF, H 2 O 2 and OH -

(d)The reaction of 5-decyne with ${\text{BH}}_{\text{3}}$, THF, ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ and ${}^{\text{ - }}\text{OH}$ produced decan-5-one as the product. The reaction can be given as:

Step 9: Reaction of alkyne with H 2 O , H 2 SO 4 and HgSO 4

Alkynes react with ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$, ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$ and ${\mathbf{HgSO}}_{\mathbf{4}}$ to form ketones. The reaction of a terminal alkyne with these reagents yields a methyl ketone.

Step 10: Reaction of 5-decyne with H 2 O , H 2 SO 4 and HgSO 4

(e)The reaction of 5-decyne with ${\text{H}}_{\text{2}}\text{O}$, ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ and ${\text{HgSO}}_{\text{4}}$ produces decan-5-one as the product. The reaction can be given as:

Step 11: Reaction of alkyne with excess H 2 and Pd/C catalyst

Alkynes get converted to alkanes when it reacts with ${\mathbf{H}}_{\mathbf{2}}$ in the presence of Pd/C as the catalyst. The conversion stops at alkene if Lindlar’s catalyst serves as the reagent.

Step 12:Reaction of 5-decyne with excess H 2 and Pd/C catalyst

(f)The reaction of 5-decyne with excess ${\text{H}}_2$ and Pd/C as the catalyst produces decane as the product. The reaction can be given as: