InterviewSolution
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InterviewSolution
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Lucas reagent produces cloudiness immediately withA. `2`-methylpropan`1-ol`B. Butan-`2-ol`C. `2`-methylpropan-`2-ol`D. `CH_(3)CH_(2)Cl` |
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Answer» Correct Answer - D Lucas test is based on the difference in reactivity of three classes of alcohols with `HCl` and distinguishes them from one another. The Lucase reagent, conc.`HCl` and anhydrous `ZnCl_(2)`, converts soluble alcohols to the corresponding alkyl chlorides which are insoluble in the reaction mixture and these appear as a cloudiness or a second more dense layer.A `3^(@)ROH` reacts immediately , a `2^(@)` alcohol reacts within `5`minutes and a `1^(@)ROH` does not react at all at room temperature. `ZnCl_(2)`, a strong Lewis acid , encourages an `S_(N)1` mechanism (i.e. formation of intermediate carbocation ) for formation of th ealkyl chlorides. Thus , the rate of reaction of the alcohols (decided by the stability of carbocations) is : `3^(@) gt 2^(@) gt 1^(@)` `CH_(3)-underset((3^(@)"alcohol")"soluble") underset(2-"Methylpropan-2-ol") underset(OH)underset(|)overset(CH_(3))overset(|)(C)-CH_(3)underset("anhyd".ZnCl_(2))overset("Conc.HCl")rarr CH_(3)-underset("Insoluble")underset(Cl)underset(|)overset(CH_(3))overset(|)(C)-CH_(3)` Remember , Lucas test is useful only for lower alcohols with six or fewer carbon atoms because initially the alcohol must be soluble in the reagent to get protonated. Alcohols having more than six carbon atoms are not soluble , so two layers are present at the start. |
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