Summary of Preparations
Phenols and Aryl Halides
The hydroxy group in a phenol molecule exhibits a strong activating effect on the benzene ring because it provides a ready source of electron density for the ring. This directing influence is so strong that you can often accomplish substitutions on phenols without the use of a catalyst.
Halogenation
Phenols react with halogens to yield mono-, di-, or tri-substituted products, depending on reaction conditions. For example, an aqueous bromine solution brominates all ortho and para positions on the ring.
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Likewise, you can accomplish monobromination by running the reaction at extremely low temperatures in carbon disulfide solvent.
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Nitration
Phenol, when treated with dilute nitric acid at room temperature, forms ortho- and para-nitrophenol.
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Sulfonation
The reaction of phenol with concentrated sulfuric acid is thermodynamically controlled. At 25°C, the ortho product predominates while at 100°C, the para product is the major product.
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Notice that at both 25° and 100°, initially an equilibrium is established. However, at the higher temperature, the equilibrium is destroyed and the more thermodynamically stable product is produced exclusively.
Kolbe reaction
The reaction of a phenoxide ion with carbon dioxide to produce a carboxylate salt is called the Kolbe reaction.
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The Kolbe Reaction progresses via a carbanion intermediate.
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In this reaction, the electron deficient carbon atom in carbon dioxide is attracted to the electron rich π system of the phenol. The resulting compound undergoes keto-enol tautomerization to create the product.
