Question

Write the principal reaction product or products, if any, of \(0-\) cresol with \(\mathrm{CO}_{2}, \mathrm{~K}_{2} \mathrm{CO}_{3}, 240^{\circ}\)

Short answer

The principal reaction product of o-cresol with CO2 and K2CO3 at 240°C is o-hydroxybenzoic acid, formed via the Kolbe-Schmitt reaction.

Step-by-step solution

Identify the reactants and reaction conditions

We have o-cresol as our main reactant, which has the chemical formula C7H8O and structure of a phenolic compound with a methyl group at the ortho position. The reaction conditions include the presence of carbon dioxide (CO2) and potassium carbonate (K2CO3) at a temperature of 240°C.

Determine the role of K2CO3 and CO2 in the reaction

Under the given reaction conditions, potassium carbonate (K2CO3) will first react with o-cresol to form an o-cresolate salt. This is because K2CO3, as a base, will deprotonate the acidic phenolic hydroxyl group of o-cresol. After deprotonation, the phenoxide formed can react with the carbon dioxide (CO2); the o-cresolate salt will act as a nucleophile and CO2 as an electrophile.

Identify the reaction type and expected product(s)

The reaction between the o-cresolate salt and CO2 under increasing temperature is known as the Kolbe-Schmitt reaction or carboxylation reaction. This type of reaction results in the formation of a salicylic acid derivative. In this particular case, with o-cresol as the starting phenol, the product will be o-hydroxybenzoic acid, along with the release of K2CO3. The overall reaction can be represented as: o-Cresol + K2CO3 + CO2 -> o-Hydroxybenzoic acid + 2 K2CO3 (at 240°C)

Key concepts

o-cresol

o-Cresol is a type of phenol, which means it is an organic compound that contains a hydroxyl group (-OH) bonded directly to an aromatic hydrocarbon group. In the case of o-cresol, its structure features a methyl group (CH₃) attached to the benzene ring at the ortho position relative to the hydroxyl group. This arrangement is what gives o-cresol its distinct properties. Being a phenolic compound, o-cresol is slightly acidic and can participate in reactions where the hydroxyl group can donate a proton. This acidity plays an important role in many reactions, including the Kolbe-Schmitt reaction.

• Formula: C₇H₈O
• Structure: Methyl group at ortho position to the OH group
• Properties: Slightly acidic due to phenolic OH group

Understanding the structure and reactivity of o-cresol is essential in predicting the outcome of reactions it is involved in, such as its ability to form o-cresolate ion when reacted with bases like potassium carbonate.

carboxylation reaction

The carboxylation reaction refers to a chemical reaction in which a carboxyl group (-COOH) is introduced into a molecule. This type of reaction is fundamental in organic chemistry, as it converts organic molecules into carboxylic acids. In the specific case of o-cresol, carboxylation occurs through the Kolbe-Schmitt reaction, a well-known process used to synthesize salicylic acid derivatives.
During the reaction, o-cresol first reacts with potassium carbonate to form o-cresolate, which is an intermediate phenoxide ion. This phenoxide then attacks carbon dioxide as a nucleophile. The carbon dioxide acts as an electrophile, facilitating the introduction of a carboxyl group into the aromatic ring of o-cresol.

• Steps: Formation of o-cresolate, followed by electrophilic attack of CO₂
• Products: Conversion of o-cresol into carboxylic acid derivatives
• Importance: Generates compounds with important industrial and pharmaceutical applications

The final product in this carboxylation reaction is o-hydroxybenzoic acid, showcasing the utility of carboxylation in transforming simple phenols into more complex organic acids.

o-hydroxybenzoic acid

o-Hydroxybenzoic acid is the principal product of the Kolbe-Schmitt reaction involving o-cresol. It is characterized by its chemical structure, which includes both hydroxyl and carboxyl groups attached to an aromatic benzene ring. This compound is also known as salicylic acid, a chemical widely used in the pharmaceutical industry, particularly for its role in producing aspirin and as a component in various skin care products.

• Structure: Aromatic ring with ortho OH and COOH groups
• Uses: Essential in pharmaceutical (aspirin) and cosmetic industries
• Relevance: Demonstrates the value of carboxylation in industrial chemistry

Understanding the synthesis and applications of o-hydroxybenzoic acid helps students appreciate the practical applications of organic reactions, such as the Kolbe-Schmitt reaction, in everyday products.