Question

The correct set of reagent to carry out following conversion is $$\mathrm{CH}_{3}-\mathrm{COOH} \longrightarrow \mathrm{HCOOH}$$ (A) (i) \(\mathrm{N}_{3} \mathrm{H}, \mathrm{H}_{2} \mathrm{SO}_{4}\) (ii) \(\mathrm{CHCl}_{3}, \mathrm{NaOH}\) (iii) \(\mathrm{H}_{3} \mathrm{O}^{+}\) (B) (i) \(\mathrm{SOCl}_{2}\) (ii) \(\mathrm{CH}_{2} \mathrm{~N}_{2}\) (iii) \(\mathrm{Ag}_{2} \mathrm{O}\) (iv) \(\mathrm{H}^{+}\) (C) (i) \(\mathrm{NH}_{3}, \Delta\) (ii) \(\mathrm{NaOBr}\) (iii) \(\mathrm{NaNO}_{2} / \mathrm{HCl}\) (D) None of these

Short answer

The correct set of reagents to carry out the given conversion (CH3COOH to HCOOH) is found in option (B): (i) SOCl2 (ii) CH2N2 (iii) Ag2O (iv) H+

Step-by-step solution

Check Option (A)

Option (A) provides us with three steps: (i) N3H, H2SO4 (ii) CHCl3, NaOH (iii) H3O+ However, this set of reagents doesn't provide the required reduction and will not lead to the desired product. So, option (A) is not the correct choice.

Check Option (B)

Option (B) provides four steps: (i) SOCl2 (ii) CH2N2 (iii) Ag2O (iv) H+ In this set of reagents, SOCl2 will convert the carboxyl group to an acyl chloride, followed by the conversion of acyl chloride to diazo compound with CH2N2, then reduction with Ag2O, and finally, acidification with H+. This set of reagents does follow the required reduction process and will lead to the desired product: Formic acid (HCOOH). Therefore, option (B) is the correct choice.

Check Option (C)

Option (C) provides three steps: (i) NH3, Δ (ii) NaOBr (iii) NaN02/HCl Although these reagents can provide a reaction pathway, they will not lead to the desired Formic acid product. So, option (C) is not correct.

Conclusion

Based on our analysis, the correct set of reagents to carry out the given conversion (CH3COOH to HCOOH) is found in option (B): (i) SOCl2 (ii) CH2N2 (iii) Ag2O (iv) H+

Key concepts

Reagent Selection

Reagent selection is a crucial step in any organic conversion reaction. The right reagents enable chemists to carry out desired transformations in an efficient and controlled manner. In our given problem, we are tasked with converting acetic acid (\(\mathrm{CH}_3\mathrm{COOH}\)) to formic acid (\(\mathrm{HCOOH}\)). This transformation requires careful selection of reagents that enable not only the reduction of the molecule but also appropriate modification of functional groups.
By examining option (B), we identify a series of transformations:

• Using \(\mathrm{SOCl}_2\) converts the carboxylic group into an acyl chloride by replacing the hydroxyl group (-OH) with a chloride (-Cl). This step is crucial because it primes the structure for further conversion.
• The introduction of \(\mathrm{CH}_2\mathrm{N}_2\) facilitates the conversion to a diazo compound, a vital intermediary step in our transformation.
• Finally, using \(\mathrm{Ag}_2\mathrm{O}\) and \(\mathrm{H}^+\) triggers the reduction required, completing the conversion to formic acid.

Together, this set of reagents takes advantage of specific chemical properties and transformations, allowing a precise and effective transformation from acetic acid to formic acid.

Carboxylic Acid Transformation

Carboxylic acid transformation involves changing the functional group of a carboxylic acid into another functional group, often to alter reactivity or to form a new structure entirely. In the context of converting acetic acid (\(\mathrm{CH}_3\mathrm{COOH}\)) into formic acid (\(\mathrm{HCOOH}\)), it requires several key steps.
The first step in option (B) is the conversion of the carboxyl group into an acyl chloride using \(\mathrm{SOCl}_2\). This step replaces the carboxylic group's hydroxyl with a more reactive chloride. This change makes it easier to transform into other functional groups.
Next, the formed acyl chloride reacts with \(\mathrm{CH}_2\mathrm{N}_2\) to create a diazo compound. This is a transient and reactive intermediate that can undergo further transformation. By carefully managing the conditions under which this reaction occurs, chemists can direct this intermediate towards the desired product with minimal side reactions.
Finally, the diazo compound can be reduced using \(\mathrm{Ag}_2\mathrm{O}\) followed by acidification with \(\mathrm{H}^+\). This sequence of steps successfully transforms the acetic acid into formic acid, showcasing the power and precision of carboxylic acid transformations in organic chemistry.

Oxidation and Reduction in Organic Chemistry

Oxidation and reduction reactions are among the most fundamental chemical reactions in organic chemistry. These reactions involve the transfer of electrons, which leads to changes in the oxidation states of the molecules involved. In organic transformations like the conversion from acetic acid (\(\mathrm{CH}_3\mathrm{COOH}\)) to formic acid (\(\mathrm{HCOOH}\)), understanding the balance between oxidation and reduction processes is vital.
In the examined option (B), the reduction occurs in the latter stages of the transformation. The diazo intermediate formed after \(\mathrm{CH}_2\mathrm{N}_2\) reacts with the acyl chloride undergoes a reduction reaction. The reagent \(\mathrm{Ag}_2\mathrm{O}\) is crucial as it promotes the reduction process, facilitating the rearrangement of bonds and electron movement toward the desired product.

• Oxidation generally involves the increase of oxygen atoms or the removal of hydrogen, whereas reduction usually involves adding hydrogen or removing oxygen.
• In this conversion, starting from a more oxidized form (acetic acid) to a less oxidized form (formic acid), it implies the removal of a carbon atom in form of a diazomethane transformation and further reduction to the acid.

Understanding oxidation and reduction allows chemists to predict the outcomes of reactions and to tailor transformations to craft specific molecules, as demonstrated with the acetic to formic acid conversion.