Predict the final product (Z) in the following sequence of...

Predict the final product $(Z)$ in the following sequence of reactions:
$$
p \text {-Cresol } \xrightarrow{\mathrm{NaOH}} \xrightarrow{\text { (ii) } \mathrm{CO}_2 / \text { Pressure }} \xrightarrow{\text { (iii) } \mathrm{H}_3 \mathrm{O}^{\oplus}}(\mathrm{Z})
$$

Key Concepts

Kolbe-Schmitt Reaction

The Kolbe-Schmitt reaction is a carboxylation process in which a phenolate ion reacts with carbon dioxide under high pressure and temperature to form a salicylic acid derivative. This reaction is important in organic synthesis for installing a carboxylic acid group onto an aromatic ring, particularly in positions ortho to an activating hydroxyl group.

Phenolate Ion Formation

Phenolate ion formation is the first step in the Kolbe-Schmitt reaction, where a phenol is deprotonated by a base such as sodium hydroxide. This deprotonation increases the electron density on the aromatic ring and makes it more reactive towards electrophilic attack, setting the stage for subsequent carboxylation.

Electrophilic Aromatic Carboxylation

Electrophilic aromatic carboxylation involves the introduction of a carboxyl group directly onto an aromatic ring. In the context of the Kolbe-Schmitt reaction, the phenolate ion acts as a nucleophile that attacks carbon dioxide, an electrophile, under high pressure conditions. This process is a specific application of electrophilic aromatic substitution, where the incoming electrophile (CO2) is added to the aromatic system.

Directed Ortho Substitution

Directed ortho substitution is a concept that explains the regioselectivity observed in many electrophilic aromatic substitutions. In the Kolbe-Schmitt reaction, the negative charge on the phenolate ion is delocalized over the ring with a preference for the ortho positions relative to the hydroxyl group. This directive effect ensures that the carboxylation occurs predominantly at the position ortho to the -OH group, leading to the formation of salicylic acid derivatives.

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