Phenol
| English | Chinese | Pinyin |
|---|---|---|
| phenol | 苯酚 | běn fēn |
| phenylamine | 苯胺 | běn àn |
| diazonium salt | 重氮盐 | zhòng dàn yán |
| phenoxide | 苯氧 | běn yǎng |
| bromination | 溴化 | xiù huà |
The ring that's acidic
- Phenol 苯酚 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.
Phenol reaction lab
Classify phenol reactions by the role of the aromatic OH group.
Phenol is:
The –OH is bonded straight to the aromatic ring, changing both the –OH and the ring chemistry.
Phenol is a weak acid that reacts with sodium hydroxide.
The –OH on the ring is more acidic than in an alcohol.
Making and reacting
- Make it: cool phenylamine 苯胺 with $\text{NaNO}_2$ + dilute acid (below 10 °C) → a diazonium salt 重氮盐; warm with water → phenol.
- Reactions:
- with NaOH(aq) → sodium phenoxide 苯氧 + water (alcohols don't react with NaOH — phenol is more acidic).
- with sodium → sodium phenoxide + hydrogen.
- bromination 溴化 with bromine water (RT, no catalyst) → 2,4,6-tribromophenol (white precipitate).
Phenol is acidic because the phenoxide charge spreads into the ring
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.
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.
Match each term to its meaning.
Each item links the term to its correct meaning.
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.
The activated ring lets phenol brominate in cold bromine water — no catalyst — to 2,4,6-tribromophenol
Carbolic soap contains phenol, once widely used as an antiseptic.
The acidity order is:
Phenol is the most acidic of the three because the phenoxide charge is delocalised into the ring.
Phenol's reactions
- Phenol reacts with sodium hydroxide (it is acidic) and with bromine water (the ring is activated).
- Bromine water decolourises and a white precipitate forms — no UV needed.
Phenol is a low-melting solid that turns pink as it oxidises in air.
You've got it
- 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