Substitution Reactions of Alcohols, Enols, and Phenols at Oxygen

Substitution Reactions of Alcohols, Enols, and Phenols at Oxygen 

As noted above, most of the reactions that might be listed as substitution at oxygen are to be considered as addition reactions in this work. However, it is worthwhile emphasizing a few of those reactions here. 

When simple primary alkyl halides are permitted to react with alkoxide anions, substitution of the alkoxide for the halide occurs or, alternatively, the alkyl group has been substituted for the hydrogen which was on oxygen. Variants of this reaction, the Williamson ether synthesis, have been seen before as a substitution reaction at carbon (of the alkyl hahde) and will be seen again as an addition reaction of alcohols. 

the reaction between methyl iodide and the anion of 2-methyl-2-propanol (terr-butoxide) to form tm-butyl methyl ether is used to demonstrate the process in which a methyl group has been substituted for the proton originally on the oxygen of 2-methyl-2-propanol (tert-butanol) (Equation 8.21). The example of Equation 8.21 is also used to emphasize that the ether (rm-butyl methyl ether) cannot be prepared from the reaction between methoxide anion and 2-iodo-2-methylpropane (or indeed any 2-halo-2-methylpropane) because elinnnation would intrude (Equation 8.22). 

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