Question

100. Compound ‘A’ on treatment with copper at $300°\mathrm{C}$ gives ‘B’ and a gas ‘C’. It is possible to get back ‘A’ from B and C. In presence of ‘D,’ both B and A on treatment with a certain reagent give the same compound ‘E,’ which on treatment with ‘A,’ gives compound F with a fruity smell. Identify the compounds and isomer of ‘F’.

Answer 1

Part 1: Generally alcohols when treated with Copper $\left(\mathrm{Cu}\right)$ at $300°\mathrm{C}$ give aldehyde and hydrogen gas.

For example, when Methanol $\left({\mathrm{CH}}_3\mathrm{OH}\right)$ is treated with Copper at $300°\mathrm{C}$, Methanal $\left(\mathrm{HCHO}\right)$ and hydrogen gas $\left({\mathrm{H}}_2\right)$ are formed.

The reaction involved is: $\underset{\mathrm{Methanol}}{{\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right)}\underset{300°\mathrm{C}}{\overset{\mathrm{Cu}}{\to }}\underset{\mathrm{Methanal}}{\mathrm{HCHO}}\left(\mathrm{l}\right)+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Part 2: Methanal on reduction with hydrogen gas in the presence of Sodium borohydride $\left({\mathrm{NaBH}}_4\right)$ gives Methanol.

The reaction involved is: $\underset{\mathrm{Methanal}}{\mathrm{HCHO}\left(\mathrm{l}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}\stackrel{{\mathrm{NaBH}}_4}{\to }\underset{\mathrm{Methanol}}{{\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right)}$

Part 3: Both Methanol and Methanal on treated with acidified Potassium dichromate $\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$ gives the same compound Methanoic acid $\left(\mathrm{HCOOH}\right)$.

The reaction involved is: $\underset{\mathrm{Methanol}}{{\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right)}+\left[\mathrm{O}\right]\stackrel{\mathrm{acidified}{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7}{\to }\underset{\mathrm{Methanoic}\mathrm{acid}}{\mathrm{HCOOH}\left(\mathrm{l}\right)}$

$\underset{\mathrm{Methanal}}{\mathrm{HCHO}\left(\mathrm{l}\right)}+\underset{\mathrm{Nascent}\mathrm{Oxygen}}{\left[\mathrm{O}\right]}\stackrel{\mathrm{acidified}{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7}{\to }\underset{\mathrm{Methanoic}\mathrm{acid}}{\mathrm{HCOOH}\left(\mathrm{l}\right)}$

Part 4: Methanoic acid when reacts with Methanol, Methyl methanoate $\left({\mathrm{HCOOCH}}_3\right)$ and water $\left({\mathrm{H}}_2\mathrm{O}\right)$is formed. This reaction is called esterification reaction. The ester Methyl methanoate formed has a fruit like smell.

The reaction involved is: $\underset{\mathrm{Methanoic}\mathrm{acid}}{\mathrm{HCOOH}\left(\mathrm{l}\right)}+\underset{\mathrm{Methanol}}{{\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right)}\to \underset{\mathrm{Methyl}\mathrm{methanoate}}{{\mathrm{HCOOCH}}_3\left(\mathrm{l}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Part 5: Isomer of Methyl methanoate is Acetic acid or Ethanoic acid $\left({\mathrm{CH}}_3\mathrm{COOH}\right)$.

Hence,

• Compound A is Methanol.
• Compound B is Methanal.
• Gas C is hydrogen gas.
• Compound D is acidified Potassium dichromate.
• Compound E is Methanoic acid.
• Compound F is Methyl methanoate.
• An isomer of F is Ethanoic acid.