Ethers are relatively non-reactive in comparison to other functional classes. Thus they are often used as solvents when harsh very basic reactions conditions, such as Grignard, organ lithium and sodium compounds, Ethers are sensitive to acidic cleavage and will undergo oxidation slowly.
When an ether is reacted with excess H-X the ether is converted to the corresponding alkyl halides.
The first alkyl halide is generated as follows. Protonation activates the ether for subsequent nucleophilic attack by the halide(X-).
The alcohol from above is then converted to the second alkyl halide as follows.
Ethers containing tertiary alkyl groups will undergo SN1 and sometimes elimination.
With phenyl ethers, the final products are phenol and an alkyl halide. Recall that phenol can not undergo SN1 or SN2 reactions so it is not converted to the corresponding halide.