Question

The reaction which is wrongly represented among the following is (a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Cl}+\mathrm{NaI} \underset{\Delta}{\stackrel{\text { acetone }}{\longrightarrow} \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{I}+\mathrm{NaCl}}\) (b) \(\mathrm{CH}_{3} \mathrm{COOAg}+\mathrm{Br}_{2} \stackrel{\mathrm{CCl}_{4} / \mathrm{reflux}}{\longrightarrow} \mathrm{CH}_{3} \mathrm{Br}+\mathrm{AgBr}+\mathrm{CO}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{COOAg}+\mathrm{I}_{2} \stackrel{\mathrm{CCl}_{4} / \text { reflux }}{\longrightarrow} \mathrm{CH}_{3} \mathrm{I}+\mathrm{AgI}+\mathrm{CO}_{2}\) (d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{Cl}_{2} \stackrel{775 \mathrm{~K}}{\longrightarrow} \mathrm{ClCH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{HCl}\)

Short answer

a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Cl}+\mathrm{NaI} \underset{\Delta}{\stackrel{\text { acetone }}{\longrightarrow} \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{I}+\mathrm{NaCl}\) b) \(\mathrm{CH}_{3} \mathrm{COOAg}+\mathrm{Br}_{2} \stackrel{\mathrm{CCl}_{4} / \mathrm{reflux}}{\longrightarrow} \mathrm{CH}_{3} \mathrm{Br}+\mathrm{AgBr}+\mathrm{CO}_{2}\) c) \(\mathrm{CH}_{3} \mathrm{COOAg}+\mathrm{I}_{2} \stackrel{\mathrm{CCl}_{4} / \text { reflux }}{\longrightarrow} \mathrm{CH}_{3} \mathrm{I}+\mathrm{AgI}+\mathrm{CO}_{2}\) d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{Cl}_{2} \stackrel{775 \mathrm{~K}}{\longrightarrow} \mathrm{ClCH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{HCl}\) Answer: d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{Cl}_{2} \stackrel{775 \mathrm{~K}}{\longrightarrow} \mathrm{ClCH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{HCl} \)

Step-by-step solution

Write Each Reaction

Write the given reactions clearly and concisely: a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Cl}+\mathrm{NaI} \underset{\Delta}{\stackrel{\text { acetone }}{\longrightarrow} \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{I}+\mathrm{NaCl}\) b) \(\mathrm{CH}_{3} \mathrm{COOAg}+\mathrm{Br}_{2} \stackrel{\mathrm{CCl}_{4} / \mathrm{reflux}}{\longrightarrow} \mathrm{CH}_{3} \mathrm{Br}+\mathrm{AgBr}+\mathrm{CO}_{2}\) c) \(\mathrm{CH}_{3} \mathrm{COOAg}+\mathrm{I}_{2} \stackrel{\mathrm{CCl}_{4} / \text { reflux }}{\longrightarrow} \mathrm{CH}_{3} \mathrm{I}+\mathrm{AgI}+\mathrm{CO}_{2}\) d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{Cl}_{2} \stackrel{775 \mathrm{~K}}{\longrightarrow} \mathrm{ClCH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{HCl}\)

Analyze Each Reaction

a) The reaction is a nucleophilic substitution reaction (SN2), where the chloride group is replaced by an iodide group. The atoms and charges are conserved, and the reaction is feasible. This reaction seems to be correct. b) The reaction shows the decomposition of silver(I) ethanoate (CH3COOAg) in the presence of bromine. The silver is replaced by a bromine atom, forming methyl bromide (CH3Br) and silver bromide (AgBr). Carbon dioxide (CO2) is also released. This reaction is known as the Hunsdiecker reaction and seems to be correct. c) Similar to reaction b), this reaction shows the decomposition of silver(I) ethanoate in the presence of iodine, resulting in the formation of methyl iodide (CH3I) and silver iodide (AgI), along with the release of carbon dioxide (CO2). This is also a Hunsdiecker reaction and seems to be correct. d) In this reaction, propene (CH3CH=CH2) reacts with chlorine gas (Cl2) at high temperature (775 K). The expected reaction would involve the addition of Cl2 to the double bond, yielding 1,2-dichloropropane (ClCH2CH2CH3) with all of the chlorine atoms participating in the reaction. However, the reaction provided shows the formation of allyl chloride (ClCH2CH=CH2) and HCl, which is not the expected outcome. Therefore, this reaction is incorrect.

Identify Incorrect Reaction

The incorrect reaction among the given reactions is: (d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{Cl}_{2} \stackrel{775 \mathrm{~K}}{\longrightarrow} \mathrm{ClCH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}+\mathrm{HCl}\)

Key concepts

Nucleophilic Substitution Reaction

Nucleophilic substitution reactions are fundamental in organic chemistry. These reactions are characterized by the replacement of a leaving group by a nucleophile. In the specific reaction given in the exercise, \[ \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Cl} + \mathrm{NaI} \underset{\Delta}{\stackrel{\text { acetone }}{\longrightarrow} \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{I} + \mathrm{NaCl}} \] the chloride ion is substituted by an iodide ion. This is an example of an \(S_N2\) reaction, which proceeds through a direct displacement mechanism.Key features of \(S_N2\) reactions include:

• A single concerted step where the nucleophile attacks the electrophilic center from the opposite side of the leaving group.
• Inversion of configuration at the carbon center if it is chiral, known as Walden inversion.
• Dependence on the strength of the nucleophile and the nature of the leaving group, with iodide being a particularly strong nucleophile.

This reaction is facilitated by using a polar aprotic solvent like acetone, which stabilizes the ions and prevents the nucleophile from becoming solvated.

Silver(I) Ethanoate Decomposition

Decomposition reactions involving silver(I) ethanoate are known as Hunsdiecker reactions. In this type of reaction, silver(I) carboxylates react with a halogen, typically yielding an alkyl halide and carbon dioxide. This reaction is represented as:\[ \mathrm{CH}_{3} \mathrm{COOAg} + \mathrm{Br}_{2} \stackrel{\mathrm{CCl}_{4}/ \mathrm{reflux}}{\longrightarrow} \mathrm{CH}_{3} \mathrm{Br} + \mathrm{AgBr} + \mathrm{CO}_{2} \]The mechanism involves several important steps:

• Formation of a halogen-silver intermediate where silver bonds to the halogen.
• Breakdown of the intermediate, facilitating the release of carbon dioxide and formation of the alkyl halide.
• This typically requires the reaction to be conducted under reflux conditions, ensuring sufficient energy to drive the reaction forward.

The importance of this reaction lies in its ability to facilitate the conversion of carboxylate salts to useful organic halide compounds, aiding synthetic processes in chemistry.

Allylic Chlorination

Allylic chlorination is a type of radical substitution in organic chemistry that typically happens at relatively high temperatures. In the described incorrect reaction, \[ \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2} + \mathrm{Cl}_{2} \stackrel{775 \mathrm{~K}}{\longrightarrow} \mathrm{ClCH}_{2}-\mathrm{CH}=\mathrm{CH}_{2} + \mathrm{HCl} \]propene reacts with chlorine to form allyl chloride.Here are key features of allylic chlorination:

• It involves the generation of radical intermediates, which lead to product formation.
• Typically, this reaction will produce halogenated compounds at the allylic position, which is the adjacent position to a double bond.
• The product distribution can be highly dependent on reaction conditions, such as temperature and concentration of reactants.

The actual product in expected allylic chlorination would generally involve a different distribution of substituted chlorines or the addition across the double bond, not just the singular formation of allyl chloride.