Lucas Test

Lucas reagent is a mixture of concentrated HCl and anhydrous ZnCl2 (ZnCl2 acts as a Lewis-acid catalyst that helps ionise the alcohol). At room temperature, a TERTIARY alcohol reacts IMMEDIATELY, giving an insoluble alkyl chloride that appears as turbidity (e.g. 2-methylpropan-2-ol gives 2-chloro-2-methylpropane at once). A SECONDARY alcohol gives turbidity only after about 10 minutes (e.g. propan-2-ol gives 2-chloropropane slowly). A PRIMARY alcohol (e.g. ethanol) shows NO reaction at room temperature; turbidity appears only on heating. The differing rates trac …