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Question: How will you distinguish between the following pairs? Write chemical equation (i) \(C{H_3}OH\) and...

How will you distinguish between the following pairs? Write chemical equation
(i) CH3OHC{H_3}OH and C2H5OH{C_2}{H_5}OH
(ii) Propane-1-ol and Propan-2-ol
(iii) Propane-1-ol and Methylpropan-2-ol
(iv) Ethanol and Propan-1-ol

Explanation

Solution

For the following differentiation of the compound we use Iodoform test. Iodoform test is used to check the presence of carbonyl compound with the structure R−CO−CH3R-CO-C{{H}_{3}} and alcohols with the structure R−CH(OH)−CH3R-CH(OH)-C{{H}_{3}} in the given unknown substance.

Complete Solution :
Iodoform reaction is the reaction of a sample compound with I2{I_2} and NaOH/KOH to produce iodoform. This reaction helps in identification of carbonyl compounds and hydroxyl compounds.
Carbonyl compound with the structure R−CO−CH3R-CO-C{{H}_{3}} and alcohols with the structure R−CH(OH)−CH3R-CH(OH)-C{{H}_{3}} show iodoform reaction.

(i) – From methanol (CH3OHC{H_3}OH) and (C2H5OH{C_2}{H_5}OH), ethanol (C2H5OH{C_2}{H_5}OH) is the one who gives iodoform reaction. Iodoform reactions of these compounds with are:
CH3−OH →NaOHI2 No reactionC{{H}_{3}}-OH\,\xrightarrow[NaOH]{{{I}_{2}}}\text{ No reaction}
C2H5OH→NaOHI2 CHI3+HCOONa{{C}_{2}}{{H}_{5}}OH\xrightarrow[NaOH]{{{I}_{2}}}\text{ }CH{{I}_{3}}+HCOONa

(ii)- From propane-1-ol (CH3−CH2−CH2−OHC{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-OH) and Propan-2-ol (CH3−CH(CH3)−OHC{{H}_{3}}-CH(C{{H}_{3}})-OH), propan-2–ol is the one who give results of iodoform reaction. Iodoform reactions of these compounds with are:
CH3−CH2−CH2−OH →NaOHI2 No reactionC{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-OH\ \xrightarrow[NaOH]{{{I}_{2}}}\text{ No reaction}
CH3−CH(CH3)−OH →NaOHI2 CHI3 + CH3COONaC{{H}_{3}}-CH(C{{H}_{3}})-OH\ \xrightarrow[NaOH]{{{I}_{2}}}\text{ }CH{{I}_{3}}\,+\,C{{H}_{3}}COONa

(iii)- Among Propane-1-ol ( CH3−CH2−CH2−OHC{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-OH) and Methylpropane-2-ol (CH3−C(CH3)2−OHC{{H}_{3}}-C{{(C{{H}_{3}})}_{2}}-OH), Methylpropan-2-ol is the one which give precipitation on iodoform reaction. Iodoform reactions of these compounds with are:
CH3−CH2−CH2−OH →NaOHI2 No reactionC{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-OH\ \xrightarrow[NaOH]{{{I}_{2}}}\text{ No reaction}
CH3−C(CH3)2−OH→NaOHI2 CHI3+CH3−CO−CH3C{{H}_{3}}-C{{(C{{H}_{3}})}_{2}}-OH\xrightarrow[NaOH]{{{I}_{2}}}\text{ }CH{{I}_{3}}+C{{H}_{3}}-CO-C{{H}_{3}}

(iv)- From Ethanol (CH3−CH2−OHC{H_3} - C{H_2} - OH) and Propane-1-ol (CH3−CH2−CH2−OHC{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-OH), Ethanol is the one who gives iodoform reaction. Iodoform reactions of these compounds with are:
C2H5OH→NaOHI2 CHI3+HCOONa{{C}_{2}}{{H}_{5}}OH\xrightarrow[NaOH]{{{I}_{2}}}\text{ }CH{{I}_{3}}+HCOONa
CH3−CH2−CH2−OH →NaOHI2 No reactionC{{H}_{3}}-C{{H}_{2}}-C{{H}_{2}}-OH\ \xrightarrow[NaOH]{{{I}_{2}}}\text{ No reaction}
Therefore, Iodoform reaction is the tool with the help of which we can distinguish the given compound pairs.
So, the correct answer is “Option B”.

Note: The major fact which should be important here is that since ethanol does not have R−CH(OH)−CH3R-CH(OH)-C{{H}_{3}} formula but still shows iodoform reaction . Ethanol is the only primary alcohol which gives yellow precipitate of iodoform.