Problem 17 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The products of reaction of alcoholic silver nitrite with ethyl bromide are(a) ethane (b) ethene (c) nitroethane (d) ethyl alcohol (e) ethyl nitrite

Step-by-Step Solution

Answer

The main product is (c) nitroethane (C_2H_5NO_2).

Step 1: Understand the Reaction

The reaction involved here is between ethyl bromide and alcoholic silver nitrite. This is a nucleophilic substitution reaction where silver nitrite ( AgNO_2 ) is used. Determine the type of products formed by this substitution.

Step 2: Identify Nucleophile Behavior

Silver nitrite ( AgNO_2 ) can produce two nucleophiles: the nitrite ion ( NO_2^- ) and nitrosyl ion ( ONO^- ). Assess which one will primarily react with ethyl bromide ( C_2H_5Br ).

Step 3: Determine Main Reaction Pathway

With ethyl bromide, the major pathway involves the nitrite ion's nitrogen acting as the nucleophile, leading to the formation of nitro compounds, predominantly C_2H_5NO_2 (nitroethane).

Step 4: Account for Possible Side Products

While the formation of nitroethane is predominant, the nitrosyl ion can also react to some extent, but less favorably, potentially leading to the formation of ethyl nitrite ( C_2H_5ONO ).

Step 5: Determine the Correct Option

Since nitroethane ( C_2H_5NO_2 ) is predominantly formed in the reaction, evaluate the options to see if this matches any. Based on this analysis, the answer would logically be nitroethane.

Key Concepts

Ethyl Bromide

Ethyl bromide, also known as bromoethane, is a chemical compound often used in various organic synthesis reactions. It is classified as an alkyl halide, featuring a bromo group (-Br) attached to an ethyl group. This structure makes ethyl bromide a prime candidate for nucleophilic substitution reactions, where the bromine atom can be replaced by a nucleophile.
Key characteristics of ethyl bromide include:

• Clear and colorless liquid.
• Used as an intermediary in pharmaceutical and chemical manufacturing.
• A density of about 1.46 g/cm³ and a boiling point of approximately 38 °C.

In the context of reactions, the presence of a leaving group like the bromine atom, which is stable when detached, facilitates the overall process of substitution. When ethyl bromide comes into contact with strong nucleophiles, these nucleophiles can replace the bromine atom, resulting in various reaction products.

Silver Nitrite

Silver nitrite (AgNO_2) is an inorganic compound that plays a crucial role in substitution reactions. In its form, it features both a cation (Ag⁺) and anions like nitrite ion (NO_2⁻). This composition allows AgNO_2 to act as a source of nitrite ions, which then become the key nucleophile in substitution processes.
Important points about silver nitrite include:

• Appears as a white to grayish solid.
• Decomposes upon exposure to light, requiring storage in dark, airtight containers.
• Its reaction with alkyl halides, like ethyl bromide, leads to prominent usage in chemical synthesis.

In reactions, the nitrite ion, derived from silver nitrite, replaces the bromine atom on the alkyl halide, typically favoring the nitrogen atom in the nitrite ion as the reactive site. This results in the formation of nitro compounds.

Nitroethane

Nitroethane is an organic compound synthesized predominately through the reaction of ethyl bromide with silver nitrite. It primarily results from the nucleophilic substitution reaction where the nitrite ion's nitrogen atom is the key participating base. This compound is crucial in various industrial applications, including solvent use and chemical synthesis.
Characteristics of nitroethane include:

• Colorless and oily liquid with a sweet, fruity odor.
• Boiling point of about 114 °C and density around 1.05 g/cm³.
• Used as a precursor to pharmaceuticals and pesticides.

In a substitution reaction, nitroethane emerges as the main product when the nitrite ion reacts with ethyl bromide. It is noteworthy that although ethyl nitrite can also form, nitroethane is significantly favored due to the nitrite ion's orientation.

Reaction Mechanism

The reaction between ethyl bromide and silver nitrite follows a classic nucleophilic substitution mechanism. In this process, the nitrite ion acts as the nucleophile, targeting the carbon atom bonded to the bromine. This leads to the cleavage of the C-Br bond, with the bromine leaving and the nitrite replacing it.
This mechanism encompasses:

• A nucleophile (nitrite ion) pairing with an electrophile (carbon in ethyl bromide).
• The departure of bromine as a leaving group.
• Substitution resulting primarily in nitroethane.

The detailed pathway involves the nitrite ion’s nitrogen being the primary point of attachment due to its reactivity, driving the overall reaction towards the formation of nitroethane. While some ethyl nitrite may manifest as a side product, the orientation and structure of the nitrite ion confer a higher tendency towards forming nitro compounds, illustrating a preference in reactivity.