Reactions with Ethers

REACTIONS WITH ETHERS

One way to make an ether is to prepare them from alcohols or their conjugate bases. The Williamson Ether Synthesis reaction involves the mixing of an alkoxide nucleophile with an alkyl halide. It becomes more difficult when an asymmetric ether is being made as some side chains are preferred to be made over others. In this reaction, a RO-Na+ salt is mixed with a brominated alkane, causing a combination of the two to make an ether.

The acid-catalyzed dehydration of small primary alcohols is a special way of making symmetrical ethers. It the reaction, sulfuric acid (H2SO4) plus ethanol (CH3CH2OH) at 110-130 degrees Celsius will make diethyl ether. If you’ll remember this type of reaction at high temperatures (over 150 degrees Celsius), the reaction favors the making of the alkene instead. This type of reaction doesn’t work for mixed ethers (asymmetrical ethers) because it gives more than one product.

Cleavage of ethers can occur with the addition of an acidic halide molecule, like HI, HBr, or HCl. This will result in an alcohol formation plus an alkane. This works well in situations of aliphatic ethers but does not work as well with aromatic (aryl) ethers. If a phenoxy-aliphatic ether is treated with these acidic molecules, phenol is always made because it is difficult to cleave the oxygen atom from the phenyl (benzene) side chain. What this looks like is seen in figure 66:

Figure 66.

Ethers that have a benzene group on either side will not be able to be cleaved by the addition of acids. Overall, however, the most common reaction of ethers is the cleavage of the CO bond by adding strong acids. The intermediary seen is the conjugate acid of the ether molecule. Typical reactions involve mixing a halide acid and getting a breakdown product that includes the alkyl halide plus water. Figure 67 shows this reaction type:

Figure 67.