Examkin

Question

Difficulty: HardAlkanoic Acids, Esterification, Saponification, Fats, and Oils

Propanoic acid is heated under reflux with ethanol in the presence of concentrated tetraoxosulfate(VI) acid to produce a sweet-smelling liquid ester. This ester is separated and subsequently boiled under reflux with aqueous potassium hydroxide until saponification is complete. Which pair of organic products is isolated from the saponification mixture?

  1. Potassium propanoate and ethanolAnswer
  2. B
    Potassium ethanoate and propan-1-ol
  3. C
    Propanoic acid and ethanol
  4. D
    Ethanoic acid and propan-1-ol

Answer

The isolated products of the alkaline hydrolysis are potassium propanoate and ethanol.
In the initial esterification reaction, propanoic acid and ethanol react in the presence of concentrated tetraoxosulfate(VI) acid catalyst to form ethyl propanoate (C2H5COOCH2CH3\text{C}_2\text{H}_5\text{COOCH}_2\text{CH}_3). When ethyl propanoate is subsequently hydrolyzed under basic conditions with aqueous potassium hydroxide (saponification), the carbonyl-oxygen ester linkage is irreversibly cleaved. This forms the potassium salt of the carboxylic acid (potassium propanoate) and regenerates the alcohol (ethanol).

Step-by-Step Solution

1
Identify the ester formed in the esterification step
Propanoic acid (C2H5COOH\text{C}_2\text{H}_5\text{COOH}) + Ethanol (C2H5OH\text{C}_2\text{H}_5\text{OH}) →conc. H2SO4\xrightarrow{\text{conc. H}_2\text{SO}_4} Ethyl propanoate (C2H5COOCH2CH3\text{C}_2\text{H}_5\text{COOCH}_2\text{CH}_3) + Water (H2O\text{H}_2\text{O})
Esterification combines the alkanoic acid acyl group (C2H5CO-\text{C}_2\text{H}_5\text{CO-}) with the alkoxy group (-OCH2CH3\text{-OCH}_2\text{CH}_3) of the alkanol.
2
Determine the saponification reaction of ethyl propanoate with potassium hydroxide
Ethyl propanoate (C2H5COOCH2CH3\text{C}_2\text{H}_5\text{COOCH}_2\text{CH}_3) + KOH(aq)→\text{KOH(aq)} \rightarrow Potassium propanoate (C2H5COOK\text{C}_2\text{H}_5\text{COOK}) + Ethanol (C2H5OH\text{C}_2\text{H}_5\text{OH})
Alkaline hydrolysis cleaves the ester bond to produce the potassium salt of the alkanoic acid and the free alkanol.

Key Concept

Alkaline Hydrolysis (Saponification) of Esters
Estimated Time:2m 0s
Rate this question

Topics

Alkanoic Acids, Esterification, Saponification, Fats, and Oils

More questions from this topic