Examkin

Question

Difficulty: MediumAlkanols: Classification, Reactions, Industrial Preparation, and Fermentation

When an unknown alkanol is warmed with acidified potassium heptaoxodichromate(VI) (K2Cr2O7K_2Cr_2O_7) solution, the orange solution turns green and an alkanone is produced. Which of the following compounds undergoes this reaction?

  1. Propan-2-olAnswer
  2. B
    Propan-1-ol
  3. C
    2-Methylpropan-2-ol
  4. D
    Ethanol

Answer

Propan-2-ol is a secondary alkanol that undergoes oxidation to form an alkanone (propanone), changing the color of acidified potassium heptaoxodichromate(VI) from orange to green.
Propan-2-ol is a secondary alkanol (CH3−CH(OH)−CH3CH_3-CH(OH)-CH_3). Upon oxidation with acidified K2Cr2O7K_2Cr_2O_7, the orange dichromate(VI) ions (Cr2O72−Cr_2O_7^{2-}) are reduced to green chromium(III) ions (Cr3+Cr^{3+}), and the secondary alcohol is converted into propanone (CH3COCH3CH_3COCH_3), which belongs to the alkanone family.

Step-by-Step Solution

1
Classify the given alkanols by structural type (primary, secondary, or tertiary).
Propan-1-ol and ethanol are primary alkanols; propan-2-ol is a secondary alkanol; 2-methylpropan-2-ol is a tertiary alkanol.
The reaction outcome of alkanol oxidation depends strictly on the classification of the hydroxyl-bearing carbon atom.
2
Determine the oxidation product for each classification type.
Primary alkanols oxidize to alkanals (and further to alkanoic acids); secondary alkanols oxidize to alkanones; tertiary alkanols resist mild oxidation.
Secondary alkanols have one hydrogen atom on the hydroxyl carbon, which allows dehydrogenation to form a carbonyl double bond (C=OC=O) bounded by two alkyl groups (ketone/alkanone).
3
Match the specified product (alkanone) to the correct compound.
Propan-2-ol oxidizes to propanone (CH3COCH3CH_3COCH_3), which is an alkanone.
Only the secondary alkanol propan-2-ol yields an alkanone.

Key Concept

Oxidation of Alkanols (Primary, Secondary, and Tertiary Classification)
Estimated Time:1m 0s
Rate this question

Topics

Alkanols: Classification, Reactions, Industrial Preparation, and Fermentation

More questions from this topic