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Ether cleavage
Ether cleavage refers to chemical substitution reactions that lead to the cleavage of ethers. Due to the high chemical stability of ethers, ether cleavage is only possible under strongly acidic or extremely basic conditions.
In organic chemistry, ether cleavage is an acid catalyzed nucleophilic substitution reaction. Depending on the specific ether, cleavage can follow either SN1 or SN2 mechanisms. Distinguishing between both mechanisms requires consideration of inductive and mesomeric effects that could stabilize or destabilize a potential carbocation in the SN1 pathway. Usage of Hydrohalic acids takes advantage of the fact that these agents are able to protonate the ether oxygen atom and also provide a halide anion as a suitable nucleophile. However, as ethers show similar basicity as alcohols (pKa of approximately 16), the equilibrium of protonation lies on the side of the unprotonated ether and cleavage is usually very slow at room temperature.
In organometallic chemistry, ether cleavage refers to the decomposition of etheric solvents by extremely basic metallorganic agents. Cyclic ethers are especially susceptible to ether cleavage, but acyclic ethers can be cleaved as well.
== SN1 Ether cleavage ==
The unimolecular SN1 mechanism proceeds via a carbocation (provided that the carbocation can be adequately stabilized). In the example, the oxygen atom in methyl ''tert''-butyl ether is reversibly protonated. The resulting oxonium ion then decomposes into methanol and a relatively stable ''tert''-butyl cation. The latter is then attacked a nucleophile halide (here bromide), yielding ''tert''-butyl bromide.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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