Question

The reagent that reacts with nitromethane to fo methylhydroxylamine is (a) \(\mathrm{Zn} / \mathrm{NaOH}\) (b) \(\mathrm{Sn} / \mathrm{HCl}\) (c) \(\mathrm{Zn} / \mathrm{NH}_{4} \mathrm{Cl}\) (d) \(\mathrm{Zn} / \mathrm{HCl}\)

Short answer

The reagent is Zn / NH_4 Cl (option c).

Step-by-step solution

Understanding the Reaction

The reaction in question involves the reduction of nitromethane ( CH_3NO_2 ) to methylhydroxylamine ( CH_3NHOH ). This type of reaction is generally a reduction process as it involves the addition of hydrogen or loss of oxygen.

Identifying the Reagents

We need to select the correct reagent pair from the given options that can reduce nitromethane to methylhydroxylamine. The options provided include different combinations of metals and acid/base solutions which are commonly used for reduction reactions.

Evaluating Each Option

Let's evaluate each option: - (a) Zn / NaOH : Zinc with a base might be used in some reductions, but it does not typically reduce nitro groups to hydroxyl-amines. - (b) Sn / HCl : Tin with hydrochloric acid is a strong reducing agent but more known for nitro group reductions to amines, not hydroxylamines specifically. - (c) Zn / NH_4 Cl : Zinc with ammonium chloride is a known system for reducing nitro compounds to hydroxylamines. - (d) Zn / HCl : Zinc with hydrochloric acid would commonly reduce the nitro group all the way to an amine.

Conclusion and Selection

From our evaluation, the Zn / NH_4 Cl system is the most specific and suitable choice for reducing nitromethane to the more selective intermediate, methylhydroxylamine. This method is known for its ability to stop at the hydroxylamine stage rather than proceeding all the way to an amine.

Key concepts

Nitromethane Reduction

Nitromethane reduction is a chemical process where nitromethane \((\text{CH}_3\text{NO}_2)\) is converted into a different compound by adding hydrogen or removing oxygen. In this exercise, the target compound formed from nitromethane is methylhydroxylamine \((\text{CH}_3\text{NHOH})\). Reduction reactions are usually identified by a decrease in the oxidation state of the molecule involved.

In the context of organic chemistry, nitro groups \((-\text{NO}_2)\) are often transformed into other functional groups like amines \((-\text{NH}_2)\) or hydroxylamines \((-\text{NHOH})\) through reduction. This transformation is significant because it allows chemists to modify and synthesize more complex molecules in a controlled fashion.

Reductions can be carried out using various reagents. The choice of reagent affects whether the reaction will stop at the intermediate hydroxylamine stage or proceed further to an amine. Understanding this distinction helps in selecting the suitable reagent for the desired level of reduction.

Methylhydroxylamine Synthesis

Methylhydroxylamine is a specific product obtained from the reduction of nitromethane. The synthesis involves converting the nitro group to a hydroxylamine group, which is a selective process.

To achieve this, chemists often use systems that ensure the reaction does not proceed further to a complete reduction to an amine. This step-control is crucial when methylhydroxylamine is the desired product.

Methylhydroxylamine is an important intermediate often used in further reactions, making its selective synthesis vital. By using specific reagent systems, the process can be controlled effectively, achieving a high yield of methylhydroxylamine. Such selective reaction conditions showcase the skill of chemists in balancing reaction conditions to obtain specific products.

Reagent Selection for Reduction

Choosing the right reagent combination is essential in reduction reactions to achieve the desired transformation. In this exercise, different combinations of metals and acids or bases were evaluated to find the most effective for reducing nitromethane to methylhydroxylamine.

Each reagent system brings its own advantages:

• Zinc with NaOH: Though a good system for various reductions, it doesn’t specifically target nitro-to-hydroxylamine transformation.
• Tin with HCl: A strong reducing pair known for converting nitro groups to amines, but not stopping at hydroxylamines.
• Zinc with NH₄Cl: The best choice here, as this combination is adept at reducing nitro groups to hydroxylamines without further reduction to amines.
• Zinc with HCl: Effective in reductions, yet typically fully reduces nitro groups to amines.

The key to selecting a suitable reagent is understanding the reactivity of the metal and the nature of the accompanying solution (acid or base). For targeting **methylhydroxylamine**, the zinc/ammonium chloride system is particularly useful, as it allows conversion to the hydroxylamine product while preventing further reduction.