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Give characteristics tests of Lucas reagent with alcohols. |
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Answer» Solution :Lucas reagent isa mixture of concentrated HCI and anhydrous ` ZnCI_(2)` . It is used to distinguish between primary , secondary and tertiary alcohols. Alcohol with Lucas reagent forms an alkyl chkloride ,R -CI which is insoluble and gives cloudiness and forms separate layer. The time REQUIRED for cloudiness to appear is based on the type of the alcohol and its reactivity. (1) Primary alcohol : It reacts with the Lucas reagent very slowly and on heating forms alkyl chloride . The separation of a layer takes PLACE after a long time on heating . ` underset(" ETHYL alcohol") (C_(2)H_(5) -OH) + underset("conc.")(HCI) overset(" anhydrous" ZnCl_(2)) underset(Delta) tounderset(" ethyl chloride")(C_(2)H_(5)-CI) + H_(2)O` (2) Secondary alcohol : It reacts with the Lucas reagent much faster to form alkyl chloride. The cloudiness and separtion of layer takes place after five minutes. `CH_(3)-underset("isopropyl alcohol")underset(OH)underset(|)(CH)-CH_(3)+ underset("conc.")("HCI") overset("anhydrous "ZnCl_(2))underset("room TEMP.")to CH_(3)-underset("isopropyl chloride")underset("CI")underset(|)(CH) - CH_(3) + H_(2)O` (3) Tertiary alcohol : It reacts immediately with the Lucas reagent at room temperature to form alkyl chloride. The cloudiness and separation of layer takes place instantaneously . `CH_(3)- underset("tert-butyl alcohol")underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-OH+HCl underset(ZnCl_(2))overset("room temp.")to CH_(3)- underset("tert-butyl chloride")underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-Cl +H_(2)O` |
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