6.1.1 Phenol Flashcards
What is phenol
phenol is an aromatic compounr with a hydroxyl group (-OH) directly bonded to the benzene ring.
Also known as phenyl alcohol - C₆H₅OH
Why is phenol not just its component parts of alcohol and arene
The presence of the 2 functional groups so close together means they affect each other’s reactivity
name: a phenol with COOH on the next carbon
2-hydroxybenzoic acid
name: a phenol with an NO₂ group on the next carbon
2-nitrophenol
name: a benzene with CH₂CH₂OH attached
2-phenylethanol
outline phenol’s reactions as an alcohol
- phenol cannot be oxidised by acidified dichromate (Cr₂O₇²⁻/ H⁺)
- phenols are very weak acids
- phenols react with sodium (Na)
- phenols react with carboxylic acids to form esters
- soluble in water
Explain why unlike alcohols, phenol cannot be oxidisd by acidified dichromate (Cr₂O₇²⁻/ H⁺)
Phenols can’t be oxidised by acidified dichromate because there is no hydrogen on the C-OH
explain how phenol is a weak acid
- When dissolved in water, phenol partially dissociates forming the phenoxide ion and a proton.
- Phenol is more acidic than alcohols but less acidic than carboxylic acids.
This can be seen through ethanol not reacting with NaOH (a strong base) or Na₂CO₃ (a weak base). Phenol and carboxylic acid reacts with NaOH, but only carboxylic acid reacts with weak bases such as Na₂CO₃
Describe phenol’s reaction with NaOH
Phenol reacts with NaOH to form the salt, sodium phenoxide and water in a neutralisation reaction.
The O⁻Na⁺ is ionic so is displayed with charges
When only Na reacts ¹/₂H₂
Describe how phenols react with carboxylic acids
Phenols react with carboxylic acid to form esters and water
Outline phenol’s reactions as an arene
elecrophilic substitution:
- bromination
- nitration
Describe phenol’s bromination
phenol reacts with bromine without needing a halogen carrier.
It is therefore more reactive than benzene.
When phenol undergoes bromination the bromine is decolourised and a white precipitate forms.
The reaction: C₆H₅OH + 3Br₂ → C₆H₅OHBr₃ + 3HBr
C₆H₅OHBr₃ is the white precipitate
can be done at room temperature
describe phenol’s nitration
phenol reacts readily with dilute nitric acid at room temperature.
It produces a mixture of 2-nitrophenol and 4-nitrophenol as products and water
H₂SO₄ as a catalyst is not required
compare the reactivity of phenol and benzene
Bromine and nitric acid react more readily with phenol than they do with benzene. Phenol is nitrated with dilute nitric acid rather than concentrated nitric acid as well as sulfuric acid as with benzene.
Why is phenol more reactive than benzene
The OH group activates the ring, the lone pair of electrons from the p-orbital of the oxygen of the OH group is delocalised into the ring. The electron density is increase compared to benzene (6e⁻ over 6 atoms to 8e⁻ over 7 atoms).
The larger electron density means that electrophiles are more attracted and can be polarised.
