Question

The compound which reacts with excess bromine to produce \(2,4,6\)-tribromophenol, is : (1) 1,3 -cyclohexadiene (2) 1, 3-cyclohexanedione (3) salicylic acid (4) cyclohexanone

Short answer

Salicylic acid

Step-by-step solution

Understand the Problem

Identify the correct compound that reacts with excess bromine to form 2,4,6-tribromophenol. Notice the bromination pattern specifically on the phenol ring.

Analyze the Options

Evaluate each compound and determine if they are capable of forming a phenol structure that can be brominated at the 2,4, and 6 positions. Check each compound step by step.

Examine 1,3-cyclohexadiene

1,3-cyclohexadiene is a diene, and does not contain the phenol functional group. Thus, it is not a candidate.

Examine 1,3-cyclohexanedione

1,3-cyclohexanedione contains keto groups but does not possess a phenol group, hence it cannot form 2,4,6-tribromophenol.

Examine Salicylic Acid

Salicylic acid contains a phenol group and a carboxylic acid group at the ortho position. With excess bromine, it can undergo bromination at the 2,4, and 6 positions on the phenol ring to form 2,4,6-tribromophenol.

Examine Cyclohexanone

Cyclohexanone is a ketone and does not have a phenol group, making it unable to form 2,4,6-tribromophenol.

Select the Appropriate Compound

After examining all options, Salicylic acid is the only compound that can react with excess bromine to produce 2,4,6-tribromophenol.

Key concepts

Bromination

Bromination is a chemical reaction that introduces bromine atoms into a compound. This process is especially significant in organic chemistry to convert aromatic compounds into more reactive derivatives.
In our scenario, bromination is used to add three bromine atoms to the phenol ring in salicylic acid. The presence of the phenol group and the ortho positioning of substituents makes it easier for bromine to attack at the 2, 4, and 6 positions. Excess bromine ensures that all three positions are brominated, resulting in 2,4,6-tribromophenol.
This type of specific and controlled bromination is an excellent example of electrophilic aromatic substitution, where bromine acts as the electrophile.

Phenol Functional Group

The phenol functional group is a crucial player in organic reactions. It consists of a hydroxyl group (-OH) attached to a benzene ring. This setup enhances the reactivity of the benzene ring, enabling various substitutions.
Phenols are more reactive towards electrophilic substitution reactions compared to benzene, due to the electron-donating effect of the hydroxyl group. This makes positions ortho and para to the hydroxyl group more susceptible to attack by electrophiles, like bromine.
In the case of salicylic acid, which has a phenol group, this enhanced reactivity results in the substitution of hydrogen atoms at the 2, 4, and 6 positions on the benzene ring when reacted with excess bromine, forming 2,4,6-tribromophenol.

Salicylic Acid

Salicylic acid is a well-known compound often used in skincare for its anti-inflammatory and exfoliating properties. This aromatic compound contains both a phenol group and a carboxylic acid group.
In our exercise, salicylic acid's phenol group is key to forming 2,4,6-tribromophenol. Reacting salicylic acid with excess bromine leads to the bromination of its phenol ring at the 2, 4, and 6 positions. This process is facilitated by the electron-donating nature of the hydroxyl group, which activates the benzene ring for electrophilic attack.
The carboxylic acid group at the ortho position influences the bromination pattern slightly but does not interfere with the main phenol-led mechanism. Therefore, salicylic acid is the ideal starting compound for the formation of 2,4,6-tribromophenol.