What are phenols?
- phenols are a type of organic chemical containing a hydroxyl group -OH functional group directly bonded to an aromatic ring
- The simplest phenol, C5H5OH has the same name as the group phenol
Are phenols weak acids?
- Phenols are less souble in water than alcohols due to the presence of a non - polar benzene ring
- When dissolved in water, phenol partially dissociates forming the phenoxide ion and a proton. The ability to partially dissociate as a weak acid
What is the order of acidity in phenol?
Most acidic
- Carboxylic acids
- Phenols
- Alcohols
How can we see the acidity of all three?
- Carboxylic acids are the most acidic as they react with strong bases such as sodium hydroxide and also react with weak bases such as sodium carbonate, producing carbon dioxide
- Phenols are weaker then carboxylic acids meaning we can distinguish between them and carboxylic acids. This is beacuse phenol reacts with sodium hydroxide but does not produce co2 with sodium carbonate
- Alcohols like ethanol do not react with NAOH or Na2Co3
What is the reaction of phenol with sodium hydroxide and what does it form?
- It is a neutralisation reaction and forms salt, sodium phenoxide and water
- notes for displayed equation
What are the electrophilic substitution reactions of phenol?
- bromination
- nitration
What occurs in the bromination of phenol?
- phenol reacts with an aqueous solution of bromine to produce 2,4,6 tribromophenol which is a white precipitate
- This reaction decolourises bromine water from orangé to colourless
- With phenol, a halogen carrier is not required and the reaction occurs at room temperature
- equation in notes
What occurs during the nitration of phenol?
- Phenol reacts readily with dilute nitric acid at room temperature to form a mixture of 2 - nitrophenol and 4 - nitrophenol
- equation in notes
Compare the reactivity of phenol and benzene?
- The bromination of phenol occurs more readily than benzene.
- Phenol reacts with dilute nitric acid rather than concentrated nitric and sulfuric acid with benzene
- Phenol also does not require a halogen carrier
- This is because in phenol, the oxygen atom on the -OH group is donated into the benzene ring
- This increases the electron density of the ring, allwoing it to polarise halogens more than benzene and increasing its reactivity
-
What is further substitution of phenol?
- like phenol forming two isomers when reacting with nitric acid, other aromatic compounds can undergo a second substitution reaction
Give an example of activation?
- bromine requires a halogen carrier to react with benzene whereas it reacts readily with phenylamine
- In this reaction as bromine reacts more readily with phenylamine, NH2 which is on the benzene ring activates the ring
Give an example of deactivation?
-Nitrobenzene reacts slower with bromine than benzene requiring a halogen carrier and high temperatures
- This means that the NO2 group deactivates the aromatic ring as the ring reacts less readily with electrophiles
Name all the positions on a benzene ring?
- Position 2 = ortho
- position 3 = meta
- position 4 = para
What are the 2,4 directing groups
- NH2 or NHR
- OH
- OR
- R or C6H5
- F, CL, BR, I
What are all 2, 4 directing groups?
- they are activating groups and increase the reactivity of the benzene ring, with the exception of halogens
What are all 3 - directing groups?
- deactivating groups which reduce the reactivity of the benzene ring
- electron withdrawing groups, decrease the density of the electron ring
