Phenol, a versatile compound with applications in various industries, is synthesized through different methods. These methods are crucial in producing phenol on both laboratory and industrial scales. The following synthesis reactions to prepare phenol are given below.
1. Synthesis of Phenols from Haloarenes:
Chlorobenzene, a representative haloarene, is obtained through the monosubstitution of the benzene ring. Under specific conditions, chlorobenzene reacts with sodium hydroxide at 623K and 320 atm to yield sodium phenoxide. Upon subsequent acidification, sodium phenoxide is converted into phenols.
2. Preparation of Phenols from Benzene Sulphonic Acid:
Sulphonation of benzene with oleum produces benzene sulphonic acid, which transforms into sodium phenoxide when heated with molten sodium hydroxide. The final step involves acidifying the sodium salt to yield phenol.
3. Preparation of Phenols from diazonium salts:
Starting from an aromatic primary amine, the formation of diazonium salts occurs upon treatment with nitrous acid (NaNO2 + HCl) at temperatures ranging from 273 to 278 K. Diazonium salts are converted into phenols through hydrolysis, accomplished by heating in water or treating with dilute acids.
4. Preparation of Phenols from Cumene:
Cumene, a hydrocarbon, serves as a precursor for phenol production. When cumene (isopropyl benzene) is exposed to air, it undergoes oxidation to form cumene hydroperoxide. Treating cumene hydroperoxide with dilute acid converts it into phenol and acetone. It’s important to note that this process generates a notable quantity of acetone as a byproduct.
5. Dow Process:
The Dow Process involves the reaction of chlorobenzene with dilute sodium hydroxide at a temperature of approximately 300°C and a pressure of 3000 psi. The schematic below illustrates the key steps in the Dow process.
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