Q43 E - Organic Chemistry (Mcmurry)

Question

How would you carry out the following reactions to introduce deuterium into organic molecules?

(a)

b. 

c. 

d.

Step-by-Step Solution

Answer

a.

b.

c. 

d. 

Step 1a: Lindlar Catalyst

Lindlar catalyst is used mainly for the selective hydrogenation of alkynes to the alkene. It is the selective catalyst used for the hydrogenation of triple bonds to cis-double bonds.

Step 2b: Sodium in liquid

Sodium in liquid ammonia is used to convert internal alkyne to trans alkene. Sodium is ionized to $N{a}^{+}$an electron.

Step 3c: D 2 O exchange

${\mathbf{D}}_2\mathbf{O}$exchange is a hydrogen-deuterium exchange reaction in which covalently bonded hydrogen is replaced by deuterium.

Due to the acidic nature of hydrogen, they can be replaced by or exchanged by deuterium using ${\mathbf{D}}_2\mathbf{O}$as a reagent.

Step 4d: exchange

${\mathbf{D}}_2\mathbf{O}$exchange is a hydrogen-deuterium exchange reaction in which covalently bonded hydrogen is replaced by deuterium.

Due to the acidic nature of hydrogen, they can be replaced by or exchanged by deuterium using ${\mathbf{D}}_2\mathbf{O}$as a reagent.

Step 5: Mechanism of reaction

a.

In this reaction, deuterium is passed in the presence of the Lindlar catalyst.  So the Lindlar catalyst converts internal alkyne to the cis alkene.

b.

c.

d.