Advices For Studying Organic Chemistry

1. Dialkyl ethers react with very few reagents other than acids.
   
   
   1. Reactive sites of a dialkyl ether: C–H bonds and –O– group.
   
   
   2. Ethers resist attack by nucleophiles and by bases.
   
   
   3. The lack of reactivity, coupled with the ability of ethers to solvate cations makes
      ethers especially useful as solvents for many reactions.
   
   
   
   


2. The oxygen of the ether linkage makes ethers basic ⇒ Ethers can react with
   proton donors to form oxonium salts.
   CH 3 CH 2 OCH 2 CH 3 + HBr H 3 CH 2 C O+ CH 2 CH 3 Br−
   An oxoniH um salt


3. Heating dialkyl ethers with very strong acids (HI, HBr, and H 2 SO 4 ) cleaves the
   ether linkage:

CH 3 CH 2 OCH 2 CH 3 + (^22) HBr CH 3 CH 2 Br+H 2 O Cleavage of an ether

A Mechanism for the Reaction

Ether Cleavage by Strong Acids

Step 1

CH 3 CH 2 OCH O+

O

2 CH 3 +HBr H 3 CH 2 C CH 2 CH 3

H

+ Br^ −

H 3 CH 2 C CH 3 CH 2 Br

H

+

Ethanol Ethyl bromide

In step 2 the ethanol (just formed) reacts with HBr (present in excess) to form a

second molar equivalent of ethyl bromide.

Step 2

H 3 CH 2 C O O+ O

H

+H Br H 3 CH 2 C

H

Br^ −+ H CH 3 CH 2 −Br

H

+ H