4.3 alcohols and phenols Flashcards
How to form alcohols from halogenoalkanes
Nucleophillic substituion with NaOH , OH- ions. (Aq)
How to form alcohols from carbonyl compounds
Primary and secondary alcohols can be formed by the reduction of carbonyl compounds.
what reducing agent is used to reduce aldehydes, ketones and carboxylic acids
- aldehydes and ketones reduced by NaBH4 to form primary and secondary alcohols but carboxylic acids require a stronger reducing agent, LiAlH4
What do alcohols react with
Hydrogen Halides
Ethanol Chloride
Carboxylic Acids
Describe the reactions of hydrogen halides with alcohols
Alcohols undergo nucleophillic substition with hydrogen halides to form a halogenoalkane. Due to the high polarity of the H-Halide bond meaning the halide can act as a nucleophile (donates pair of electrons)
Describe the reaction of alcohol with hydrogen chloride
Requires anhydrous zinc as a catalyst
Describe the reaction of alcohols with hydrogen bromide
First, add potassium bromide to alcohol then add concentrated sulphuric acid to produce hydrogen bromide in-situ.
Describe the reaction of alcohol with hydrogen iodide
First, add potassium iodide to alcohol followed by concentrated phosphoric acid H3PO4. To produce hydrogen iodide in-situ.
Why do we use phosphoric acid instead of sulphuric acid when reacting hydrogen iodide with alcohol
Sulphuric acid would oxidise the iodide ions to iodine reducing the yield of hydrogen iodide.
Describe the reaction of alcohols with ethanol chloride
Ethanoyl chloride is a type of acyl chloride which are derivates of carboxylic acids - produces an ESTER in A nucleophillic addition elimination reaction
Why is using ethanoyl chloride better than carboxylic acids
HCL fumes given off and produces better yield than using carboxylic acids.
Ethanoyl chloride however is expensive so is not cost effective in industry.
Describe the reaction the alcohols with carboxylic acids
Alcohols react with carboxylics acids to produce esters in the presence of a strong acid catalyst, Concentrated sulphuric acid in an equilibrium reaction under reflux.
Also known as esterification.
What are esters properties
Sweet smelling
Low BP
Make good solvents
Describe the acidity of phenols
Phenol is an aromatic alcohol + is weakly acidic because they can lose a Hydrogen(H+) from the OH group forming a phenoxide ion (C6H5O-)
The lone pair on oxygen overlaps with the delocalised pi electron system of the benzene ring extending the delocalisation and stabilising the phenoxide ion making phenols more acidic than alcohols.
Describe the bond strength and stability in phenols
C-O bond in phenols is shorter and stronger than in alcohol due to the double bonds from benzene ring
Therefore there’s increased electron density in the ring making it more susceptible for attack by electrophiles.
Why is phenol not soluble
Hydrophobic benzene ring out weights the hydrophilic OH group, however phenols can dissolve in NaOH
What do phenols react with
NaOH
Not Na2CO3
A Test to distinguish add sodium carbonate, a carboxylic acid will produce co2 bubbles, phenols wont react.
Describe the reaction of phenol with bromine
Aqueous bromine (electrophile) reacts with phenol to form 2-4-6-tribromophenol (white ppt) via electrophilic substitution. Orange bromine decolourises which can be a test for phenols
Reaction of phenol with ethanoyl chloride
Phenols are less reactive as nucleophiles than alcohols due to delocalisation of the oxygens lone pair into the benzene ring, so phenols dont react with carboxylic acids to form esters.
They react with ethanoyl chloride to form esters but slow reaction at room temperature so use bases like pyridine
What is the test for phenols
Add iron(III)Chloride (Fe3+) If phenol exists a purple colour should form Can be used to distinguish between phenol and aliphatic alcohol.
Activation of benzene ring
OH group on phenol activates benzene ring increasing electron density in ring via delocalisation.
Positions 2-4-6 are strongly activated due to the electron donating effect of the OH group so subsitituions prefer these positions.
