Preparation of alkanes

Question

Which of the following might be produced by the reaction of C2H5Cl and C3H7Cl with Na? I. CH4 II. C4H10 III. C5H12 A) I only B)IIandIII C)IandIII D) I and II E) I, II and III

Answer 1

Hello Alexa

 

The general reaction for the synthesis of alkanes from alkyl halides is:

 

R-X + R-X + 2Na → R-R + 2Na-X

 

REACTION #1

 

C₂H₅Cl can be re-written as CH₃CH₂-Cl.  Following the above general reaction,

 

CH₃CH₂−Cl + Cl−CH₂CH₃ (I have purposely written the structure in reverse!)

 

               ↑     ↑

 

Remove these two Cls and connect the two carbons of both alkyl groups together with a single bond between them.  This will then give the alkane:

 

CH₃CH₂−CH₂CH₃ = C₄H₁₀ (Answer choice II)

 

 

REACTION #2

 

C₃H₇Cl can be re-written as CH₃CH₂CH₂−Cl (n-propyl chloride.  NOTE!  This can also be isopropyl chloride, but for simplicity, let's leave it as n-propyl chloride).  Following the same sequence as for C₂H₅Cl, we can write this reaction as:

 

CH₃CH₂CH₂−Cl + Cl−CH₂CH₂CH₃ → CH₃CH₂CH₂−CH₂CH₂CH₃ = C₆H₁₄ (NOT an answer choice!)

 

 

REACTION #3

 

CH₃CH₂−Cl + Cl−CH₂CH₂CH₃ → CH₃CH₂−CH₂CH₂CH₃ = C₅H₁₂ (Answer choice III)

 

 

From the above 3 reactions, the final answer choice is B) II and III.