Question

The $ 1 - propanol $ and $ 2 - propanol $ can be distinguished by:
A. Oxidation with alkaline $ KMn{O_4} $ followed by reaction with Fehling’s solution.
B. Oxidation with acidic dichromate followed by reaction with Fehling’s solution.
C. Oxidation by heating with copper followed by reaction with Fehling’s solution.
D. Oxidation with conc. $ {H_2}S{O_4} $ followed by a reaction with Fehling’s solution.

Answer 1

Hint : An alcohol is defined in primary, secondary or tertiary alcohols which depends on how many carbons are attached to the carbon bearing the hydroxyl group. Primary alcohols have no other carbon, secondary ones have one carbon and tertiary alcohols have two carbons attached to the carbon bearing the hydroxyl group.

Complete Step By Step Answer:
Fehling solution is a chemical reagent which is generally used to differentiate water soluble carbohydrates and ketone functional groups. It is also used in tests for reducing and non-reducing sugar.
The reaction between aldehyde and copper ion in Fehling solution can be given as:
 $ RCHO + 2C{u^{2 + }} + 5O{H^ - } \to RCO{O^ - } + C{u_2}O + 3{H_2}O $
In case of alcohols,
According to the recorded data, it comes that $ 1 $ degree alcohol give the positive for the oxidation by heating with copper followed by the reaction with Fehling’s solution. And give a red precipitate in result.
The following reaction take place in case of $ 1 - propanol $ :
  $ C{H_3} - C{H_2} - C{H_2}OH\xrightarrow{{Cu(573K)}}C{H_3} - C{H_2} - CHO $
Gives red ppt. with Fehling′s solution
This red precipitate proves that the alcohol is primary that is 1-propanol.
But secondary alcohol does not give Fehling’s solution test. If we treat Fehling solution with secondary alcohol then there will be no red precipitate. In simple words, it fails to give the Fehling test and therefore $ 2 - propanol $ does not give red precipitate.
 $ C{H_3} - CHOH - C{H_3}\xrightarrow{{Cu(573K)}}C{H_3} - CO - C{H_3} $
(Does not give Fehling′s solution test)
By this test we can easily distinguish between $ 1 - propanol $ and $ 2 - propanol $ .
So, option C is correct.

Note :
Lucas test is also used to differentiate between primary, secondary and tertiary alcohol. Reagent used in this test is called Lucas reagent. Lucas reagent consists of anhydrous zinc chloride and hydrochloric acid.Primary alcohols do not react with Lucas reagents. White turbidity appears after $ 5 $ to $ 10 $ minutes when Lucas reagent reacts with secondary alcohols.Turbidity appears immediately when Lucas reagent reacts with tertiary alcohols.