Explain the reactions of alcohol compounds involving the cleavage of the $C-O$ bond.

(N/A) Reactions involving the cleavage of the $C-O$ bond occur in alcohols. In phenols,the $C-O$ bond cleavage only occurs upon heating with zinc dust.
$(a)$ Reaction of alcohols with $HX$ (hydrogen halides) and Lucas test:
$(i)$ Alcohols react with hydrogen halides $(HX)$ to form alkyl halides.
$R-OH + HX \rightarrow R-X + H_2O$
In this reaction,the $C-O$ bond is broken,a $C-X$ bond is formed,and the $-OH$ group is removed. This reaction proceeds via nucleophilic substitution mechanisms ($S_N1$ and $S_N2$).
The order of reactivity of hydrogen halides $(HX)$ with alcohols is $3^{\circ} > 2^{\circ} > 1^{\circ}$.
$(ii)$ Alkyl bromides are formed by heating alcohols with $48\% \ HBr$.
$(iii)$ Reaction with $HCl$ (Lucas test):
The catalyst $ZnCl_2$ is required for the reaction of primary and secondary alcohols with $HCl$. The Lucas reagent is a mixture of concentrated $HCl$ and $ZnCl_2$. $1^{\circ}, 2^{\circ},$ and $3^{\circ}$ alcohols can be distinguished using the Lucas test.
Alcohols are soluble in the Lucas reagent,but the resulting alkyl halides are immiscible,causing turbidity in the solution.
Tertiary alcohols react immediately with the Lucas reagent to form alkyl halides,causing immediate turbidity and the formation of a separate layer.
Secondary alcohols react slowly with the Lucas reagent,producing turbidity after some time,followed by the formation of a separate layer.
Primary alcohols do not react with the Lucas reagent at room temperature,so no turbidity or separate layer is observed for a long time.
Thus,the reactivity order of alcohols is $3^{\circ} > 2^{\circ} > 1^{\circ}$,allowing for the identification of $3^{\circ}, 2^{\circ},$ and $1^{\circ}$ alcohols using the Lucas test.