Question

n-propyl alcohol and isopropyl alcohol can be chemically distinguished by which reagent:
(A) $PC{{l}_{5}}$
(B) reduction
(C) oxidation with potassium dichromate
(D) ozonolysis

Answer 1

Among n-propyl alcohol and isopropyl alcohol one is a primary alcohol and the other one is a secondary alcohol. Depending on the type of alcohols, whether they are primary or secondary, they give different products on oxidation.

Complete step by step solution:
-Oxidation of n-propyl alcohol and isopropyl alcohol with potassium dichromate allows us to chemically distinguish between n-propyl alcohol and isopropyl alcohol.
-As we know, alcohols on oxidation give carbonyl compounds. When primary alcohol is oxidized, aldehydes and carboxylic acid are formed. Secondary alcohols on oxidation give ketones and tertiary alcohols cannot be oxidized without breaking the molecules carbon-carbon bonds.
-n-propyl alcohol is a primary alcohol and its reaction with potassium dichromate is given below
C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}OH\xrightarrow[{{K}_{2}}C{{r}_{2}}{{O}_{7}}/{{H}_{2}}S{{O}_{4}}]{\left[ O \right]}C{{H}_{3}}C{{H}_{2}}CHO
Thus n-propyl alcohol on oxidation with potassium dichromate gives an aldehyde.
-Isopropyl alcohol is secondary alcohol and it on oxidation with potassium dichromate gives the following reaction,
C{{H}_{3}}CH(OH)C{{H}_{3}}\xrightarrow[{{K}_{2}}C{{r}_{2}}{{O}_{7}}/{{H}_{2}}S{{O}_{4}}]{\left[ O \right]}C{{H}_{3}}COC{{H}_{3}}
Thus, isopropyl alcohol on oxidation with potassium dichromate gives a ketone.
-Therefore, the two alcohols give different products on oxidation with potassium dichromate. Moreover, the clear orange solution of potassium dichromate turns blue-green in the reactions and for isopropyl alcohol this colour change is fast and for n-propyl alcohol the colour change is slow.
-From the above discussion it's clear that the isopropyl alcohol and n-propyl alcohol can be chemically distinguished by oxidation with potassium dichromate.

Thus, the answer is option (C).

Note: It should be noted that isopropyl alcohol and n-propyl alcohol are examples of position isomers. As we know position isomers are constitutional isomers with the same functional groups and same carbon Skeleton but having a different location of functional groups. In isopropyl alcohol, the hydroxyl group is present in the second carbon atom whereas in n-propyl alcohol the hydroxyl group is present in the first carbon atom.