What is 'Z' in the following reaction sequence?
(Alcohol = colorless)
$$
\mathrm{C_3H_6} \xrightarrow[\text{CCl}_4]{\mathrm{Br_2}} \mathrm{X} \xrightarrow[\Delta]{\text{i) KOH/alcohol} \\ \text{ii) NaNH}_2} \mathrm{Y} \xrightarrow[\mathrm{Hg}^{2+}, \mathrm{H}^+]{333\,K} \mathrm{Z}
$$