Phenols Flashcards
Acidity of phenol
What is pH?
What is the ion produced?
Why its acidic?
PH-5/6
Phenoxide ion
Because the negative charge is delocalised onto the ring as the electrons in the P orbital of Oxygen and the Pi electrons of the ring overlap,this gives it stability so likely to donate H+ and is an acid
Acidity of ethanol
Ion produced?
pH?
Why not acidic?
Ethoxide ion
PH- 7.3
Not acidic- ethyl group donates electron density as alkyl groups are electron releasing, the negative charge is not delocalised so no extra stability, it’s not likely to donate H+ so not acidic
It’s neutral in aqueous solution
Ethanoic acid
pH?
Ion produced?
Why acidic?
Ethane ate ion
pH- 3
It is acidic - the negative charge is delocalised over the O atoms, the delocalisation is stronger than phenol so has more stability, likely to donate H+
Water
Ion produced
pH?
Why?
Hydroxide ion
pH-7
Slightly more likely to give up H+ than ethanol so is more acidic, but is still not classed as acidic
What is phenol?
An aromatic ring which 1 or more of the aromatic hydrogen atoms are replaced by an OH group
Why is phenol dangerous?
It’s a toxic solid so must avoid skin contact
Why doesn’t phenol behave like a typical aliphatic alcohol despite having an OH group?
One of the lone pairs of electrons in the P orbital of oxygen overlaps with the delocalised Pi electrons of the ring to form an extended Delocalised Pi system - so C-O bond has Pi character. Meaning the C-O bond is stronger than the C-O in aliphatic alcohols.
The overlaps also reduces the delta + charge on the C attached to O as its spread over the delocalised system. So the c of the c-o in phenol is less subseptible to NUCLEOPHILIC attack than the c-o in aliphatic.
Although it undergoes NUCLEOPHILIC substitution, it is less likely in phenol when compared to ethanol
Reaction of phenol with bromine or bromine water :
What is the type of reaction?
Electrophilic substitution
Reaction of phenol with bromine/Br water
What positions are subsituted?
2,4,6 positions
Reaction of phenol with bromine / Br water
What is an observation of this?
White PPT
Why is phenol more subseptible to Electrophilic substitution than benzene?
A catalyst isn’t required e.g FeBr3
Concentrated bromine not required
A mono-substituted product is not produced
Why doesn’t phenol produce an ester with a carboxylic acid and concentrated H2SO4?
Because it does not behave like a typical alcohol
What does phenol react with to produce an ester?
What is this reaction called?
Ethanoyl chloride
Called an ethanoylation RXN or NUCLEOPHILIC substitution
What does phenol and ethanoyl chloride produce?
Phenylethanoate (ester)
Reaction steps in words for preparation of aspirin
1- phenol + NaOH
2- sodium phenoxide + CO2/H+
3- salicylic acid
4- ethanoic anhydride + salicylic acid at 90 degrees
5- aspirin + ethanoic acid
What are reagents and conditions for industrial preparation of aspirin?
Ethanoic anhydride
90 degrees
Reaction test - aqueous iron (III) chloride
What reacts with iron 3 chloride and what does it produce?
The phenolic OH group (directly attached to ring) of phenol reacts with iron 3 chloride to produce a PURPLE COLOUR
In aqeous iron III chloride why don’t aliphatic alcohols give a purple colour?
Because the OH group. Is not phenolic and attached directly to the ring
What can also produce a purple colour with aqueous iron III chloride?
Other compounds that contain a phenolic OH GROUP such as salicylic acid
What are the reagents for Triiodomethane (iodoform) test
And what is seen if the compound is present?
I2 / NaOH (aq)
A positive result is seen if the fragment is present
What does the positive result consist of in the Triiodomethane iodoform test?
A yellow PPT and an antiseptic smell
What is the only 1 degree alcohol that gives a positive result in Triiodomethane test?
Ethanol.
What alcohols don’t give a positive result in Triiodomethane test?
Tertiary alcohols
Give chemical test for phenol
Aqueous iron (III) chloride
How can we distinguish phenol?
React it with iron (III) chloride and it produces a purple colour- phenolic OH reacts with it
What type of reaction is phenol with bromine?
Electrophilic substitution
Phenol produces an ester in a reaction, but with what reagent?
Ethanoyl chloride - NUCLEOPHILIC substitution to produce phenylethanoate
What is the positive result seen when phenol reacts with reagents
(Name reagents also)
Reagents are sodium hydroxide (aq) and iodine
Positive result is CH3CHOH
