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Karnataka Board PUCPUC Science 2nd PUC Class 12

An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B).

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Questions

An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-1-ene. Write equations for the reactions involved.

An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to get a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives But-1- ene. Identify (A), (B) and (C) and write chemical equations for the reactions involved.

Chemical Equations/Structures
Very Long Answer
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Solution

  1. An organic compound A with molecular formula C8H16O2 gives a carboxylic acid (B) and an alcohol (C) on hydrolysis with dilute sulphuric acid. Thus, compound A must be an ester.
  2. Further, alcohol C gives acid B on oxidation with chromic acid. Thus, B and C must contain an equal number of carbon atoms. Since compound A contains a total of 8 carbon atoms, each of B and C contains 4 carbon atoms.
  3. Again, on dehydration, alcohol C gives but-1-ene. Therefore, C is of straight chain, and hence, it is butan-1-ol. On oxidation, Butan-1-ol gives butanoic acid. Hence, acid B is butanoic acid.

Hence, the ester with molecular formula C8H16O2 is butylbutanoate.

All the given reactions can be explained by the following equations:

\[\ce{\underset{\underset{(A)}{Butyl butanoate [C8H16O2]}}{CH3CH2CH2COOCH2CH2CH2CH3} + H3O+ ->\underset{\underset{(B)}{Butanoic acid}}{CH3CH2CH2COOH} + \underset{\underset{(C)}{Butanol}}{CH3CH2CH2CH2OH}}\]

\[\ce{\underset{\underset{(C)}{Butanol}}{CH3CH2CH2CH2OH}->[{[O]} Oxidation][Chromic acid (H2CrO4)]\underset{\underset{(B)}{Butanoic acid}}{CH3CH2CH2COOH}}\]

\[\ce{\underset{\underset{(C)}{Butanol}}{CH3CH2CH2CH2OH}->[Dehydration][-H2O]\underset{But-1-ene}{CH3CH2CH=CH2}}\]

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Chapter 8: Aldehydes, Ketones and Carboxylic Acids - Exercises [Page 256]

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NCERT Chemistry Part 1 and 2 [English] Class 12
Chapter 8 Aldehydes, Ketones and Carboxylic Acids
Exercises | Q 8.11 | Page 256

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