Question

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.

Answer 1

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.

\[\begin{array}{cc}
\ce{O}\phantom{.......}\\
||\phantom{.......}\\
\ce{\underset{Butylbutanoate}{CH3CH2CH2 - C - OCH2CH2CH2CH3}}\
\end{array}\]

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

\[\begin{array}{cc}
\ce{O}\phantom{..............................................}\ce{O}\phantom{...............}\\
||\phantom{...............................................}||\phantom{...............}\\
\ce{\underset{(A)}{\underset{Butylbutanoate}{CH3CH2CH2 - C - OCH2CH2CH2CH3}} ->[dil. H2SO4] \underset{(B)}{\underset{Butanoic acid}{CH3CH2CH2 - C - OH}} + \underset{(C)}{\underset{Butan-1-ol}{CH3CH2CH2CH2OH}}}\
\end{array}\]

\[\begin{array}{cc}
\phantom{................................................}\ce{O}\\
\phantom{................................................}||\\
\ce{CH3CH2CH2CH2 - OH ->[CrO3/CH3COOH][Oxidation] \underset{(B)}{\underset{Butanoic acid}{CH3CH2CH2 - C - OH}}}
\end{array}\]

\[\ce{CH3CH2CH2CH2 - OH ->[Dehydration][-H2O] \underset{But-1-ene}{CH3CH2CH = CH2}}\]