Properties of Phenol

PHYSICAL PROPERTIES

Phenol is needle shaped solid, soon liquefies due to high hygroscopic nature. It is less soluble in water, but readily soluble in organic solvents.

Phenol has high boiling point due to presence of hydrogen bonding.

Acidity of phenol

Phenol is weak acid. It reacts with aqueous NaOH to form sodium phenoxide, but does not react with sodium bicarbonate.

The acidity of phenol is due to the stability of the phenoxide ion, which is resonance stabilized as shown below:

In substituted phenols, the presence of electron withdrawing groups at ortho and para positions such as nitro group, stabilizes the phenoxide ion resulting in an increase in acid strength. It is due to this reason that ortho and para nitro phenols are more acidic than phenol.

On the other hand, electron releasing groups such as alkyl group, do not favour the formation of phenoxide ion – resulting in decrease in acid strength.

For example: (cresol are less acidic then phenol)

CHEMICAL REACTIONS

(A) Reaction due to breaking of O – H bond

Phenol is more reactive than alcohol for this reaction because phenoxide ion is more stable than the alkoxide ion. 

Reactions of phenol due to breaking of ¾O$-$H bond are given below:

Acylation 

Fries rearrangement

Phenolic esters are converted in to o$-$and p$-$ hydroxy ketones in the presence of anhydrous AlCl₃. Generally low temperature favours the formation of p – isomer and higher temperature favour the o - isomer.

(B) Reactions due to breaking of carbon- Oxygen bond

Nucleophilic substitution reaction

Phenols are less reactive than aliphatic compound because:

(i)  $-$ OH group is present on sp² hybridised carbon. This makes C$-$O bond stronger.

(ii) ‘O’ is more electronegative than halogens. This also makes C$-$O bond stronger than

    ਌$-$X.

(iii) There is some double bond character between carbon and oxygen due to the resonance. This also makes C$-$O bond stronger.

     However it give SN under drastic condition. 

(C)     ꃪS in Phenol: It is strong activating group. 

MERCURATION

Mercuric acetate cation. [HgOAC]⁺ is a weak electrophile which substitutes in ortho and para position of phenol. Usually donating product is O�toxy mercuriphenol. The mercuric compound can be converted to iodophenol.

Miscellaneous reaction

(i)  Reaction with Zn dust

(ii) Oxidation 

(iii) Condensation with phthalic anhydride