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Question
Primary, secondary and tertiary alcohol cannot be differentiated by:
Primary, secondary and tertiary alcohol cannot be differentiated by:
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Solution
The correct option is D PCl3
Distinction of primary, secondary and tertiary alcohol by following methods:
(a) Oxidation test
(b) Lucas test
(c) Victer meyer test (best method)
(d) Catalytic dehydrogenation by Cu/300°C.
Lucas test:Lucas test is based on the difference in reactivity of primary, secondary and tertiary alcohols with hydrogen chloride. In Lucas test, an alcohol is treated with Lucas reagent (conc. HCl and ZnCl2). Turbidity is produced as halides of the substituted alcohol are immiscible in Lucas reagent. The time taken to achieve turbidity is noted and following observations are made:
In case of primary alcohol, turbidity is not produced at room temperature. However, on heating, an oily layer is formed.
In case of secondary alcohol, an oily layer is produced in 5-6 minutes. Thus, the reaction takes some time to produce turbidity.
In case of tertiary alcohol, turbidity is immediately produced as halides are easily formed.
Oxidation Test:
In oxidation test, the alcohols are oxidized with sodium dichromate. The rate of oxidation varies between primary, secondary and tertiary alcohol. On the basis of their oxidation rates, alcohols can be distinguished as:
Primary alcohol gets easily oxidized to an aldehyde and can further be oxidized to carboxylic acids too.
Secondary alcohol gets easily oxidized to ketone but further oxidation is not possible.
Tertiary alcohol doesn’t get oxidized in presence of sodium dichromate
Reaction with copper:
When the vapour of the alcohols is passed over finely-divided copper seated to 300°, primary alcohols are decomposed into hydrogen and aldehydes, secondary alcohols give hydrogen and ketones, and tertiary alcohols yield water and unsaturated hydrocarbons.
Distinction of primary, secondary and tertiary alcohol by following methods:
(a) Oxidation test
(b) Lucas test
(c) Victer meyer test (best method)
(d) Catalytic dehydrogenation by Cu/300°C.
Lucas test:Lucas test is based on the difference in reactivity of primary, secondary and tertiary alcohols with hydrogen chloride. In Lucas test, an alcohol is treated with Lucas reagent (conc. HCl and ZnCl2). Turbidity is produced as halides of the substituted alcohol are immiscible in Lucas reagent. The time taken to achieve turbidity is noted and following observations are made:
In case of primary alcohol, turbidity is not produced at room temperature. However, on heating, an oily layer is formed.
In case of secondary alcohol, an oily layer is produced in 5-6 minutes. Thus, the reaction takes some time to produce turbidity.
In case of tertiary alcohol, turbidity is immediately produced as halides are easily formed.
Oxidation Test:
In oxidation test, the alcohols are oxidized with sodium dichromate. The rate of oxidation varies between primary, secondary and tertiary alcohol. On the basis of their oxidation rates, alcohols can be distinguished as:
Primary alcohol gets easily oxidized to an aldehyde and can further be oxidized to carboxylic acids too.
Secondary alcohol gets easily oxidized to ketone but further oxidation is not possible.
Tertiary alcohol doesn’t get oxidized in presence of sodium dichromate
Reaction with copper:
When the vapour of the alcohols is passed over finely-divided copper seated to 300°, primary alcohols are decomposed into hydrogen and aldehydes, secondary alcohols give hydrogen and ketones, and tertiary alcohols yield water and unsaturated hydrocarbons.
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