Question

Choose the incorrect option about reaction: $$\mathrm{R}-\mathrm{CHO}+2{\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]}^{\oplus }+3{\mathrm{OH}}^{-}⟶\mathrm{P}+2\mathrm{Q}+2\mathrm{T}+4\mathrm{S}$$ (A) If $\mathrm{R}$ is benzene, then $(\mathrm{P})$ is benzoic acid. (B) If $\mathrm{T}$ is ${\mathrm{H}}_2\mathrm{O}$, then a bright silver mirror is produced due to ' $\mathrm{Q}$ '. (C) Reaction occurs in alkaline medium. (D) ${\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]}^{\oplus }$ is also known as Tollen's reagent.

Short answer

All of the given options (A, B, C, and D) are true; there is no incorrect statement.

Step-by-step solution

Option A

If R is benzene, then (P) is benzoic acid. When the R group is a benzene ring, the reaction will form a carboxylic acid. In this case, benzoic acid is formed, so option A is true.

Option B

If T is H₂O, then a bright silver mirror is produced due to Q. In the presence of Tollen's reagent, aldehydes get oxidized to carboxylic acids, while the silver ions in Tollen's reagent are reduced to metallic silver. The metallic silver forms a bright silver mirror on the surface of the reaction vessel, so option B is true.

Option C

Reaction occurs in an alkaline medium. Tollen's reagent contains a complex of silver ions with ammonia, which requires an alkaline environment to form. The presence of hydroxide ions (OH⁻) in the reaction further indicates that the reaction takes place in an alkaline medium, so option C is true.

Option D

[Ag(NH₃)₂]⁺ is also known as Tollen's reagent. Tollen's reagent is a solution of silver(I) complexed with ammonia, which is represented by the formula [Ag(NH₃)₂]⁺. Therefore, this option is also true. Since all options A, B, C, and D are true, there is no incorrect statement given.

Key concepts

Oxidation of Aldehydes

Aldehydes are organic compounds that contain a carbonyl group (C=O) bonded to at least one hydrogen atom. During chemical reactions, they can be oxidized to form carboxylic acids. - **The oxidation process:** - In the presence of an oxidizing agent, such as Tollen's reagent, aldehydes undergo oxidation. - The aldehyde (R-CHO) reacts to form a carboxylic acid (R-COOH). - **Tollen's reagent role:** - It acts as a mild oxidizing agent, capable of distinguishing aldehydes from ketones, as ketones do not readily oxidize to carboxylic acids under these conditions. This reaction is crucial in identifying aldehydes due to the simplicity of converting them to carboxylic acids efficiently.

Silver Mirror Test

The silver mirror test is a classical method for detecting the presence of aldehydes through a visible chemical reaction.- **How it works:** - Aldehydes, when mixed with Tollen's reagent, reduce the silver ions ( ${\text{Ag}}^{+}$ ) present in the reagent to metallic silver. - The metallic silver deposits on the inner surface of the reaction vessel, forming a lustrous silver mirror.- **Significance:** - This test is specific to aldehydes because ketones do not react similarly. - It is a visual test and serves as a hallmark confirmation for the presence of aldehyde functional groups. The silver mirror test not only identifies aldehydes but also visually demonstrates the reduction aspect of the redox process.

Alkaline Medium Reaction

Tollen's reagent requires an alkaline medium to function effectively, which involves the presence of hydroxide ions (OH⁻).- **Formation of Tollen's reagent:** - Tollen's reagent is prepared by mixing silver nitrate (AgNO₃) with aqueous ammonia (NH₃) in the presence of sodium hydroxide (NaOH). - The presence of OH⁻ ions creates an alkaline environment necessary for the formation of the silver-ammonia complex.- **Role of an alkaline medium:** - The alkaline medium facilitates the stabilization of the silver-ammonia complex, $$[\text{Ag}({\text{NH}}_3{)}_2{]}^{+}$$, which is crucial for its reactivity with aldehydes. - It ensures that the oxidation-reduction reaction proceeds smoothly, allowing the reduction of silver ions to solid silver during the silver mirror test.Thus, the alkaline medium is vital for the successful implementation of Tollen's reagent in aldehyde detection.