Dissolves toluene

phenol

What is special about phenol?

Phenol (see also lexicon article) is one of the most dangerous substances in the chemistry collection, next to bromine and conc. Sulfuric acid, but that's not what makes phenol special. The special thing about phenol is that in every textbook chapter on the chemistry of aromatics, the phenol molecule comes to the fore. Phenol is actually nothing more than a benzene with an OH group. This OH group gives the phenol new properties compared to benzene.

The phenol molecule with bond lengths and bond angles as well as in a 3D representation

This figure shows the phenol molecule in detail, especially the bond lengths and the bond angles are highlighted. On the right you can see a spatial representation of the phenol molecule.

Phenol is soluble in water

If you dissolve a few phenol crystals in a little water, you get a more or less clear solution. If you dissolve the same amount of phenol in a little more water, that doesn't work - strange, isn't it? If you then add more water, the phenol dissolves again and a clear solution is created. For more details, see the "Miscibility gap in phenol" section.

Bromination of phenol

Most high school chemistry textbooks compare the bromination of phenol to the bromination of benzene and toluene.

  • Benzene can only be brominated with the help of a catalyst such as iron bromide or aluminum bromide. See also the page "Bromination of Benzene" in the Reaction Types / Electrophilic Substitution section.
  • Toluene is easier to brominate than benzene, but a catalyst is still needed. The methyl group has a slight + I effect on the benzene ring, which increases the electron density in the benzene ring, which significantly increases the attractiveness of the benzene ring for electrophilic substituents.
  • Phenol can be brominated even more easily than toluene; a catalyst is no longer necessary here. As soon as you add bromine water to a test tube with an alkaline phenol solution, the bromine water decolorizes relatively quickly.

One should expect that the phenol bromination proceeds significantly more slowly than the toluene bromination. The OH group of the phenol has an -I effect on the benzene ring and thereby lowers the electron density and the attractiveness / reactivity of the molecule. The opposite is the case. Details can be found on the pages "+ M effect vs. -I effect in phenol" and "The second substitution" in the section "Electrophilic substitution".