Problem 134 - A Complete Resource Book in Chemistry for JEE Main

Question

The ether c1ccc(COc2ccccc2)cc1 when treated with HI produces (1) CCc1ccccc1 (2) OCc1ccccc1 (3) Ic1ccccc1 (4) Oc1ccccc1 (a) 1,3 (b) 1,2 (c) 1,4 (d) all of these

Step-by-Step Solution

Answer

Correct answer is (a) 1,3.

Step 1: Identify the Ether

The given ether is represented by the SMILES notation `c1ccc(COc2ccccc2)cc1`, which corresponds to phenyl phenyl ether, also known as diphenyl ether. Its structure includes two phenyl groups connected by an ether linkage (-O-).

Step 2: Recognize the Reaction Type

The ether is treated with hydroiodic acid (HI), a reagent known to cleave ethers. This reaction will typically break the C-O bond, resulting in the formation of two products: one will contain iodine (as a result of the attack by I-) and the other will contain an OH group.

Step 3: Predict the Cleavage Products

When phenyl phenyl ether is cleaved by HI, the bond between the oxygen and one of the phenyl rings breaks. A hydrogen atom from HI will attach to the oxygen, forming a phenol, and the iodine atom will attach to the phenyl ring.

Step 4: Determine the Expected Products

The reaction would yield iodophenol and phenol. In SMILES notation, these products correspond to `Ic1ccccc1` and `Oc1ccccc1`, respectively.

Step 5: Match with Given Options

The given options are (1) `CCc1ccccc1`, (2) `OCc1ccccc1`, (3) `Ic1ccccc1`, and (4) `Oc1ccccc1`. The correct products are represented by options (3) and (4), which match iodophenol and phenol.

Key Concepts

HI Reaction with Ethers

The HI reaction with ethers is a classic chemical process used to break the C-O bonds in ethers. Ethers are compounds with an oxygen atom connected to two alkyl or aryl groups. When reacting with strong acids like hydroiodic acid (HI), the ether's oxygen atom usually gets protonated, which weakens the C-O bond.
This leads to the cleavage of the bond, resulting in two separate molecules. One of the cleavage products contains an iodine atom because the iodide ion (I-) from HI acts as a nucleophile, attacking one carbon atom.

• HI breaks ethers by splitting them into two smaller molecules.
• The oxygen of the ether gets protonated, facilitating the breakage.
• An iodide ion bonds with one carbon, while part of the molecule forms an alcohol or phenol group.

Understanding this reaction is essential because it helps predict the outcomes of ether transformations in chemical reactions.

Diphenyl Ether

Diphenyl ether is the specific type of ether involved in the described reaction. It consists of two phenyl groups (C₆H₅) connected via an oxygen atom, giving it the formula C₆H₅OC₆H₅. Its structure is symmetrical, leading to interesting reaction possibilities when treated with HI.
This compound's noteworthy feature is its stability, although it becomes reactive in the presence of strong acids like HI.

• Its structure can be shown as two benzene rings linked by oxygen.
• Formation includes two aromatic rings that make it a crucial substrate for electrophilic and nucleophilic reactions.

When HI is introduced, the symmetric structure allows the cleavage to occur in two different positions, leading to two unique products.

Iodophenol Formation

In the reaction of diphenyl ether with HI, one key product is iodophenol. This formation happens when the C-O bond splits, and the iodide ion from HI bonds to one of the phenyl carbons.
The process involves the iodide ion becoming attached to a phenyl ring, replacing one of the hydrogen atoms in the aromatic ring. This change defines the transformation into an iodophenol.

• The iodine atom adds to a carbon attached to the now-broken ether linkage.
• Results in the presence of both an iodine atom and a hydroxyl group on different aromatic rings.
• Represents how nucleophilic substitution can modify aromatic compounds.

This transformation highlights how HI can modify aryl ethers into derivatives containing iodine.

Phenol Formation

Phenol formation is another result of the HI treatment on diphenyl ether. Here, the splitting of the C-O bond under HI's influence results in a hydroxyl group bonding with a phenyl ring. This interaction produces phenol (C₆H₅OH), a simple yet essential aromatic compound.

• The bond-ending oxygen receives a proton from HI, facilitating the hydroxyl group's formation.
• Phenol is recognized for its hydrogen bonding capabilities and acidic properties.
• Commonly, the presence of a phenol group markedly increases a molecule's reactivity due to the electron-donating nature of the hydroxyl group.

Understanding the formation of phenol through this reaction is significant in organic chemistry, showcasing how ethers can be converted into aromatic alcohols through acid cleavage.