Question

The correct statement regarding the following reaction is (A) Dry HCl gas is used to increase electrophilicity of carbonyl (B) \((\mathrm{P})\) is ethylene glycol ketal (C) If (P) is hydrolysed with aqueous acid, it gives back to reactant (D) All of these

Short answer

The correct answer is (D) All of these, as all the statements (A, B, and C) are correct regarding the reaction involving electrophilicity, ketals, and hydrolysis.

Step-by-step solution

Recall the reaction

First, let's write down the given reaction: P + dry HCl -> Reactant

Understand the effect of dry HCl gas

Dry HCl gas is used in this reaction. One common effect of dry HCl gas is to increase the electrophilicity of carbonyl compounds by protonating the carbonyl oxygen atom, making it a better electrophile and more susceptible to a nucleophilic attack.

Determine if (P) is ethylene glycol ketal

Ketals are formed by the reaction of a carbonyl with a diol (a molecule with two alcohol groups). Ethylene glycol is a diol, and the reaction with a carbonyl compound would produce an ethylene glycol ketal. Given statement (B), we should determine if (P) is indeed ethylene glycol ketal.

Hydrolysis of (P) with aqueous acid

Statement (C) states that hydrolysis of (P) with aqueous acid would give back the reactant. This is a typical characteristic of ketals as they can be readily hydrolyzed back to the parent carbonyl compound and the diol under acidic conditions.

Determine the correct statements

Now that we have discussed all the given statements, we can determine which ones are correct: (A) Dry HCl gas is used to increase electrophilicity of carbonyl. This statement is correct as HCl protonates the carbonyl oxygen, increasing its electrophilicity. (B) \((\mathrm{P})\) is ethylene glycol ketal. This statement can be correct as ketals can react with HCl and return back to carbonyl. (C) If (P) is hydrolysed with aqueous acid, it gives back the reactant. This statement is also correct, as this is a characteristic property of ketals in the presence of aqueous acid. Therefore, the correct answer is: (D) All of these.

Key concepts

The Role of Electrophilicity in Carbonyl Compounds

The concept of electrophilicity is fundamental when discussing the reactivity of carbonyl compounds. Electrophilicity refers to the ability of a chemical species to accept electrons. In carbonyl compounds, the carbon atom bonded to the oxygen atom can become an excellent electrophile under the right conditions. This is because the electronegative oxygen atom naturally pulls electron density towards itself, leaving the carbon atom electron-deficient. However, not all carbonyl compounds are equally electrophilic.
When you introduce a catalyst such as dry HCl gas, the electrophilicity increases significantly. The mechanism involves the protonation of the carbonyl oxygen by HCl. This protonation enhances the positive charge on the carbon, making it more susceptible to nucleophilic attack. Increasing electrophilicity is crucial in reactions where a nucleophile, such as a diol, needs to react with the carbonyl more readily.

• Electrophilicity explains the carbonyl's reactivity with diols.
• Protonation of oxygen makes the carbon a stronger electrophile.
• Important for initial steps in ketal formation.

Understanding electrophilicity is important for predicting the behavior of carbonyl compounds in various chemical reactions.

Ketal Formation: A Key Reaction of Carbonyls

Ketal formation is a process whereby a ketone reacts with a diol to form a ketal. This reaction is an excellent example of carbonyl chemistry. Ketals are a type of acetal that is specific to ketones. For a ketone to form a ketal, it typically reacts with a diol like ethylene glycol. This reaction occurs in the presence of an acid catalyst, such as dry HCl gas.
The process involves several key steps. The carbonyl group of the ketone acts as an electrophile, made more reactive by the presence of the acid catalyst. The diol, which contains two hydroxyl (OH) groups, acts as a nucleophile. It attacks the electrophilic carbon, leading to the formation of an intermediate. Subsequent steps, which involve removing water and stabilizing the structure, result in the formation of a stable ketal.

• Ketals form from ketones and diols in acidic conditions.
• Involves nucleophilic attack by the diol on the carbonyl carbon.
• Uses acid catalysts such as dry HCl gas.

Thus, the essence of ketal formation lies in understanding the interaction between nucleophiles and electrophiles.

Understanding Hydrolysis of Ketals

Hydrolysis of ketals is an essential reaction that demonstrates their reversibility. The process sees ketals being converted back into their original carbonyl compounds and diols. This happens when they are treated with aqueous acid, an essential characteristic that differentiates ketals from other carbonyl derivatives. Hydrolysis occurs because ketals are unstable in water, especially when exposed to an acidic environment.
Aqueous acid catalyses the reaction by protonating the ether oxygen in the ketal. This makes the ketal's structure less stable, leading to the hydrolysis process that breaks it down into alcohols and ketones. It's a fascinating process because it illustrates how chemical bonds can be both formed and broken with the right conditions. This reversibility can be practical in protecting carbonyl groups in multi-step syntheses, where you might need to perform temporary modifications without permanent alteration.

• Ketals hydrolyze back to ketones and diols in acids.
• Protonation weakens the ketal, promoting hydrolysis.
• Important for temporary protection in synthesis.

Understanding the hydrolysis of ketals enhances our knowledge about reversible reactions in organic chemistry.