Phenol
Phenol
- Phenol has an –OH joined directly to a benzene ring.
- This changes the chemistry of both the –OH group and the ring.
- It is more acidic than an alcohol, and its ring is more reactive than benzene's.
Practice
Phenol is:
The –OH is bonded straight to the aromatic ring, changing both the –OH and the ring chemistry.
Making and reacting
- Make it: cool phenylamine with $\text{NaNO}_2$ + dilute acid (below 10 °C) → a diazonium salt; warm with water → phenol.
- Reactions:
- with NaOH(aq) → sodium phenoxide + water (alcohols don't react with NaOH — phenol is more acidic).
- with sodium → sodium phenoxide + hydrogen.
- bromination with bromine water (RT, no catalyst) → 2,4,6-tribromophenol (white precipitate).
Practice
Unlike an ordinary alcohol, phenol reacts with NaOH(aq). This shows phenol is:
Phenol is acidic enough to react with NaOH, forming sodium phenoxide; alcohols are not.
Practice
Phenol with bromine water at room temperature (no catalyst) gives:
The activated ring reacts readily, brominating positions 2, 4 and 6 to give a white precipitate.
Acidity and the activated ring
- Phenol loses $\text{H}^+$ to a phenoxide ion, stabilised because the charge spreads into the ring. So acidity is:
$$\text{ethanol} < \text{water} < \text{phenol}$$
- A lone pair on the oxygen is partly delocalised into the ring, making it electron-rich — so phenol reacts under milder conditions than benzene (no catalyst, dilute reagents, room temperature). The –OH directs to 2, 4, 6.
Practice
The acidity order is:
Phenol is the most acidic of the three because the phenoxide charge is delocalised into the ring.
You've got it
Key idea
- phenol = –OH directly on a benzene ring
- it reacts with NaOH (more acidic than an alcohol); bromine water → 2,4,6-tribromophenol (white ppt, no catalyst)
- acidity: ethanol < water < phenol (phenoxide stabilised by the ring)
- the ring is activated (lone pair delocalised in), so phenol reacts under milder conditions than benzene