Or industrial methods of preparation of phenols.
Most of the industrial methods used for preparing phenols are same as used in the laboratory. However, certain phenols(including the most important one, Phenol) are produced commercially by some special methods which are quite inconvenient to use as laboratory method.
Phenol is a highly important industrial chemical because it serves as the raw material for a large number of commercial products such as aspirin , dyes, phenol-formaldehyde polymer etc. worldwide production of phenol is more than 3 million tonnes per year. A small portion of phenols, as well as cresol produced per year, comes from coal-tar but nearly all the phenols produced commercially are synthetic. Several methods have been used to synthesised phenols commercially. Some important methods for the commercial production are described as below.
The general method for the preparation of phenols is as follows.
1. From haloarenes: Dows process.
When chlorobenzene is heated with caustic soda at 3000C and 200 atm pressure, sodium phenoxide is formed which on acidification produces phenol.
2. From diazonium salt.
A diazonium salt gives phenol when warmed in presence of water.
3. From benzene sulphonate.
When sodium salt of benzene sulphonic acid is fused with caustic soda at 3000C,sodium phenoxide is obtained which on acidification produce phenol.
4. By decarboxylation of salicylic acid.
Salicylic acid undergoes decarboxylation when heated with soda lime to produce sodium phenoxide which on acidification produces phenol.
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