What happens when tertiary butyl alcohol is passed over heated copper at ${300}^{\mathrm{o}}\mathrm{C}$ ?

What is $\mathrm{Z}$ in the following sequence of reactions?

$\mathrm{Z}\stackrel{{\mathrm{PCl}}_5}{\to }\mathrm{X}\stackrel{\mathrm{AlC}.\mathrm{KOH}}{\to }\mathrm{Y}\underset{\left(\mathrm{ii}\right){\mathrm{H}}_2\mathrm{O}; \mathrm{boil}}{\overset{\left(\mathrm{i}\right)\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }}\mathrm{Z}$

Phenol $\frac{{\text{ NaNO }}_2}{\text{ conc. }{\mathrm{H}}_2{\mathrm{SO}}_4}$ Green colour $\stackrel{{\mathrm{H}}_2\mathrm{O}}{⟶}$ red colour $\stackrel{\mathrm{NaOH}}{⟶}$Blue colour

This reaction is associated with the name of :