Reaction of alcohol with hydrogen halide

Alcohols react with hydrogen halides to give alkylhalides.
ROH + HX --------> R-X + H2O
The alcohol may be primary, secondary or tertiary and hydrogen halide may be HCl, HBr or HI.
For example,
CH3CH2CH2OH + HI ------------> CH3CH2CH2I + H2O

alcohol-reaction-with-hydrogen-halides HBr

alcohol-reaction-with-hydrogen-halides HCl

To increase the yield of haloalkane a dehydrating agent like anhydrous ZnCl2 is used to remove the water formed.
In this reaction, the reactivity of alcohols decreases in the order tertiary > secondary > primary. Among hydrogen halides reactivity decreases in the order HI > HBr > HCl

 Related post Chemical properties of Alcohols and Phenols

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