Chlorobenzene to Phenol | C6H5-Cl + NaOH Reaction
When chlorobenzene is treated and heated with concentrated NaOH, phenol is given as a product. Diphenyl ether and NaCl is also formed as products. But, chlorobenzene do not react with dilute NaOH because C-Cl bond in chlorobenzene is much stronger than C-X (X=Cl, Br, I) bonds in aliphatic alkayl halide compounds.
C6H5-Cl + NaOH reaction
This reaction was used to synthesis phenol in some time ago. This reaction is called as Dow Process. Concentrated NaOH solution and 3500C temperature is required to prepare phenol from chlorobenzene.
C6H5-Cl + NaOH → C6H5-OH + C6H5-O-C6H5 + NaCl
Due to formation of diphenyl ether and sodium chloride, phenol cannot be obtained as a pure compound. Therefore, has to do a separation method to separate phenol from other compounds.
Reaction of C6H5Cl and concentrated NaOH is a nucleophilic substitution reaction.
When electron-withdrawing groups are attached to the benzene ring of chlorobenzene
When electron-withdrawing groups such as nitro groups (-NO2) are connected to the ortho and para positions relative to the chlorine atom, increases the substitution reaction with NaOH.
This means, substitution reaction of 2-Nitrochlorobenzene, 4-Nitrochlorobenzene and 2,4,6-Trinitrochlorobenzene with NaOH is much easier than chlorobenzene.
Concentration and required temperature for the substitution reaction is less in 2-Nitrochlorobenzene, 4-Nitrochlorobenzene and 2,4,6-Trinitrochlorobenzene.
Chemical compounds and their formula in this reaction
- Chlorobenzene - C6H5Cl
- Diphenyl ether - C6H5-O-C6H5
- Phenol - C6H5OH
Due to difficulties of this NaOH and chlorobenzene reaction, we can follow below reactions to prepare phenol as an alternative method. But this process takes some steps and time to complete.
Chlorobenzene to phenol through grignard reagent, benzene, nitrobenzene, aniline
- First, magnesium ethyl bromide (grignard reagent) is prepared from chlorobenzene. Then water is added to prepare phenol.
- Then, benzene reacts with concentrated nitric acid and sulfuric acid to prepare nitrobenzene (nitration of benzene).
- As next step, nitrobenzene is reduced to aniline by Sn, concentrated HCl and followed by aqueous NaOH.
- In the final step, aniline reacts with nitrous acid at room temperature to prepare phenol.
C6H5Cl + dilute NaOH, what will be the product?
With dilute NaOH, chlorine atom will not be replaced by hydroxyl ion such as aliphatic alkyl halides. When chlorine atom is joint with benzene ring, that bond is so much strong than aliphatic C-Cl bond. That's why in chlorobenzene, C-Cl bond is not broken by dilute NaOH solution.
What are the difficulties you have to face in the reaction of chlorobenzene with naoh?
This reaction needs a high temperature.To give a higher temperature, a large heat have to be produced during the reaction. That is a hard thing and expensive process, specially in industrial scale.
Are chlorobenzene and phenol have different properties?
They are very much different in chemical properties. Phenol reacts with Na, NaOH. But, chlorobenzene do not.