Protecting groups tertiary butyl ethers

Because the hydrogenolysis of the phenylmethyl (benzyl) ether in the final step occurs under neutral conditions, the tertiary alcohol function survives untouched. A tertiary butyl ether would have been a worse choice as a protecting group, because cleavage of its carbon-oxygen bond would have required acid (Section 9-8), which may cause dehydration (Section 9-2). 

The formation of mixed ethers directly from two alcohols usually gives a mixture of three products. However, it is possible to form mixed ethers in which one alkyl group is tertiary and the other is primary or secondary (Section 16.4). We carry out this acid-catalyzed reaction, converting the tertiary alcohol to a tertiary carbocation, which then reacts with the other alcohol. For example, we can protect the hydroxyl group of cyclohexanol with a tcrr-butyl group. 

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