Methods of Phenols Preparation

Phenols are the chemical compounds that have a benzene ring linked to a hydroxyl group. They are sometimes referred to as carbolic acids due to their extreme acidic character. Phenol can be substituted using either one of the Ortho meta para or the numbering system. The parental molecule should be referred to as phenol in any situation, Cresols are common names given to some phenols, for example, phenols.

Phenol Method of Preparation

There are different methods of preparation of phenols-

1. From diazonium salts

2. From Benzene Sulphonic Acid

3. By method of  Decarboxylation of Salicylic Acid

4. By Grignard Reagent

5. From Dakin Reaction

Let’s talk about each of them in detail-

1. From Diazonium salts-

It is the easiest way to prepare phenols. Phenol is formed when benzene diazonium chloride solution is combined with warm water or dilute acid, and the nitrogen gas is released.         

2. From Benzene Sulphonic Acid-

Sodium Phenoxide is produced using benzene sulphonic acid’s sodium salt with sodium hydroxide. Sodium Phenoxide is converted into phenol by treating it with dilute acid or carbon dioxide. 

3. By method of Decarboxylation of Salicylic Acid

Decarboxylation of salicylic acid with soda lime in addition to acidification with dilute hydrochloric acid will produce phenol. 

4. From Grignard Reagent

Chlorobenzene or bromobenzene will be converted into phenyl magnesium halide in the presence of dry ether. The Grignard reagent produces phenol when it reacts with oxygen and is hydrolyzed by mineral acid. 

5. From Dakin Reaction

Dakin Reaction occurs when o-o- and p-p- hydroxyl aldehydes or ketones combine with alkaline hydrogen peroxide, then hydrolysis to give o-o- and p-p-hydroxyphenol.

Industrial Method of Preparation of Phenol –

The various methods for the industrial preparation of phenol are-

1. When benzene, hydrogen chloride, and air combine at high temperature in the presence of a catalyst, cupric chloride and ferric chloride produce chlorobenzene. At a temperature of 698K, it will be hydrolyzed by steam, which gives phenol and HCl. This method of preparation is called Rasching’s process. This is a very recent method of phenol production. 

2. When chlorobenzene is heated with sodium carbonate or a 10 % solution of caustic soda and under high pressure produces a very large amount of phenol. This process is called the Dow process. 

3. When phenol is produced from cumene, then it is called isopropyl benzene. We can prepare cumene by Friedel- Craft alkylation of benzene including propene in the presence of phosphoric acid. When this is oxidized then produces cumene hydroperoxide. Cumene hydroperoxide when hydrolyzed multiple times with an aqueous acid gives phenol and propanone.  

4. Phenol can be extracted from the mid- oil fraction. When the naphthalene is separated, then the fraction is cooled down. We will use sulphuric acid to remove any impurities from the leftover oil.  Dilute caustic soda is used to get the phenol. Use sulphuric acid or even carbon dioxide to separate the aqueous layer to get phenol. We will use the method of fractional distillation to separate the layer of oil.  

Diazonium Salts-

Let’s talk about the formation of phenols from diazonium salts separately. We have discussed the process of the formation above. We know that the primary amine is reacted with nitrous acid at 273-278 K, then we will get diazonium salts. The diazonium salts which are produced are highly reactive in nature. Thus, when the salt comes in contact with warm water, they are hydrolyzed into phenols. These obtained diazonium salts can be converted to a required product of phenols by treating them with dilute acids. 

Conclusion

In this article, we have given the definition of phenols. Phenols are the chemical compounds having benzene rings linked to a hydroxyl group. They are also called carbolic acids due to their extreme acidic character. Phenol can be substituted using either one of the Ortho meta para or the numbering system. The method of preparation of phenol has been discussed in detail. We have talked about multiple methods in detail. The various ways of preparation of phenol are from diazonium salts, benzene sulphonic acid, Dakin reaction, Grignard reagent, and the method of decarboxylation of salicylic acid.