Phenol is the simplest and most important member of the series.
Preparation of phenol. Phenol is obtained by the following methods:
From Chlorobenzene (Dow Process). This involves the hydrolysis of chlorobenzene with aqueous NaOH at high temperature and pressure followed by treatment with dilute HCl.
This process was first introduced in 1928 by the Dow the chemical company of U.S.A.
From Cumene. This involves air-oxidation of cumene (Isopropyl benzene) followed by treatment with dilute HCl.
The above cumene process accounts for 80% of the total world production of phenol. The success of the method is due to the availability of benzene and propene from petroleum and to the formation of acetone, a valuable by-product.
From Sodium Benzenesulphonate. This involves the fusion of sodium benzene sulphonate with solid NaOH at 300 °C followed by treatment with dilute HCl.
From Benzenediazonium Salts. This reaction can be performed easily in the laboratory and simply requires warming a solution of benzene diazonium chloride, prepared from aniline, on a water bath at 50 °C.
The phenol is recovered by steam distillation and extracted with diethyl ether.
From Coal Tar. Coal tar provides a natural source of phenol and cresols, but nowadays provides less than 10% of the total supply. The middle oil fraction (170-240°C) of coal tar contains phenols, cresols, and naphthalene. The oil, when cooled, deposits solid naphthalene, which is removed by centrifuging the mixture. The oil left is agitated with NaOH solution when phenol and cresols dissolve as sodium salts.
Phenol is finally isolated from the resulting of phenols by fractional distillation.
Physical Properties Of Phenol.
Phenol is colorless, hygroscopic, crystalline solid (mp42C; bp 182°C). The liquid form of phenol containing about 5% water is known as carbonlic acid. Below 65.8C phenol is only partially miscible with water but above the temperature, it is miscible in all proportions. It is readily soluble in ethanol and another organic solvent. It turns pink on exposure to air and light. It has a distinctive odor. Phenol is a poison when taken orally and produces painful blisters in contact with skin. The IR absorption frequencies of phenol are: 3200-3650 cm-1 (O-H stretching); 1230 cm-1(C-O stretching) ; and 1400-1300 cm-1 (O-H bending).
Chemical Properties Of Phenol.
The reaction of phenol is the reaction of the –OH group and the benzene ring.
- About half of the total world’s production of phenol (two billion pounds) is used for making phenol-formaldehyde resins e.g., Bakelite.
- Phenol used as a starting material for drugs such as salol, Aspirin.
- Phenolphthalein and several other dyes.
- Explosives e.g., picric acid.
- Many other valuable products of common use: wood preservatives, herbicides, nylon, antiseptics (Dettol), gasoline additives, etc.