(i) Phenol is a colorless, toxic, corrosive, needle shaped solid.
(ii) Phenol soon liquifies due to high hygroscopic nature.

Unlike simple ketones, which are far more stable than their corresponding enols, the analogous equilibrium for phenol lies far on the side of the enol form which is shown in Fig.2(a). The reason for this difference is the resonance energy of the aromatic ring, which provides an important stabilization of the enol form.

Since the functional group occurs as suffix in phenol, many compounds containing hydroxyl group are named as derivatives of the parent compound phenol, as illustrated by the IUPAC names as shown in Fig.2(b).

Suffix groups such as sulfonic acid and carboxylic acid take priority, and when these groups are present the hydroxyl group is used as a modifying prefix as shown in Fig.2(c).

Phenyl ethers are named in the IUPAC system as alkoxyarenes, although the ether nomenclature is used for some compounds shown in Fig.2(d).

Phenols and their ethers are widespread in nature, and, as is usual for such compounds, trivial names abound shown in Fig. 2(e).

The methyl phenols are commonly called cresols in Fig.2(f).

The benzene diols also have common names as shown in Fig.2(g).

Phenols are fairly acidic compounds, and in this respect, markedly different from alcohols, which are even more weakly acidic than water.

Aqueous hydroxides converts phenols into their salts, aqueous mineral acid convert the salts back into the free phenols.

`underset (underset (text(Insoluble in water)) underset text(acid) text(A phenol))( ArOH) underset (H^+) overset (OH^-) (⇋) underset (underset (text(Soluble in water)) underset text(Salt) text(A phenoxide ion)) (ArO^-)`

Most phenols have `K_a` values in the neighbourhood of `10^-10` and are thus weaker acids than the carboxylic acids (`K_a` values about `10^-5`). Most phenols are weaker than carbonic acid and hence unlike carboxylic acids do not dissolve in aqueous bicarbonate solution.

`text(Industrial method :)` Phenol is a highly important industrial chemical; it serves as the raw material for a large number of commercial products ranging from asprin to a variety of plastics.

`i)` `text(Hydrolysis of chlorobenzene : (Dow's process) : )` When chlorobenzene is heated at `360^oC` and under high pressure with aqueous sodium hydroxide, it is converted to sodium phenoxide, which on acidification gives phenol. See fig.1.

The mechanism for the above reaction involves probably the formation of benzyne.

`ii)` `text(Alkali fusion of Sodium benzene sulfonate :)` Sodium benzene sulfonate is melted (fused) with sodium hydroxide (at around `350^oC` ) to produce sodium phenoxide which on acidification yields phenol. See fig.2.

`iii)` `text(From Cummene Hydroperoxide :)` It is a method for converting two relatively inexpensive organic compounds; benzene and propene into two more valuable ones-phenol and acetone. The only other substance consumed in the process is oxygen from air. See fig.3.

The mechanism of the above reactions are, See fig.4.

The second reaction is a radical chain reaction. A radical initiator forms a `3^o` benzylic radical which then forms cummene hydroperoxide. See fig.5.

The third one, resembles the carbocation rearrangements. See fig.6.

`text(Laboratory Methods :)`

`i)` `text(Alkali Fusion of Aryl Sulphonate Salts :)` Phenols may be prepared by fusion of sodium arylsulphonates with sodium hydroxide

`ii)` `text(Aromatic Nucleophilic Substitution of Nitro Aryl Halides :)` Phenols are formed when compounds containing an activated halogen atom are heated with aqueous sodium hydroxide, e.g. p-nitrophenol from p-chloronitrobenzene. See fig.7.

`iii)` `text(Hydrolysis of diazonium salts :)` When a diazonium sulphate solution is steam distilled, a phenol is produced.

`ArN_2^(+)Hoverset(-)(SO_4) + H_2O -> ArOH + N_2 + H_2SO_4`

`iv)` `text(Distillation of phenolic acids with soda-lime produces phenols, e.g. sodium salicylate gives phenol :)` See fig.8.