4.3 Alcohols & Phenols
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Draw a phenol
Explain the reactivity of phenol (diagram too)
• lone pair on the oxygen is drawn to the ring • increases electron density of the ring, activating it • ring is able to induce dipoles
Describe the test for phenols
• Ferric chloride test, FeCl3 • lead to deep purple solution • add bromine give white ppt
Explain the reactivity of phenol
• phenol is highly reactive due to the overlap of p-orbitals of the oxygen from the hydroxyl group and the p-orbitals of the carbons on the benzene ring of phenol • overlapping causes lone pair on oxygen to be drawn to the ring • increases electron density of the ring, activating it and making it able to induce dipoles
Explain the reactivity of benzene
• not very reactive • 3 double bonds • double bonds must be broken • molecules reacting with it must be +ve to attract electrons in the bond and break them
Explain the reactivity of cyclohexene
• very reactive • only one double bonds must be broken • can easily induce dipoles due to high delocalisation
Primary alcohol
One carbon bonded to the C-OH group
Secondary alcohol
Two carbon atoms bonded to the C-OH group
What are the methods of forming alcohols?
• halogenoalkanes by a substitution reaction • reducing aldehydes, ketones or carboxylic acids
Draw the nucleophilic substitution of a halogenoalkane
What is used in carbonyl reduction to produce alcohols?
• sodium tetrahydridiborate / NaBH4 (aldehyde and ketones) • lithium aluminium hydride (carboxylic acids)
Primary alcohol mechanism
Primary —> aldehyde —> carboxylic acid • H+/Cr2O7 at each stage • distillation in first stage • reflux to go alcohol to carboxylic acid
Secondary alcohol mechanism
Secondary —> ketone • H+/Cr2O7
Tertiary alcohol mechanism
No change occurs
Why is the boiling temperature of methanol higher than that of chloromethane?
• methanol has hydrogen bonding • chloromethane has VdW • hydrogen bonds stronger than VdW
Reagents and conditions for conversion of alcohol to carboxylic acid
• acidified potassium dichromate • heat
What is meant by heterolytic bond fission?
• bond breaks and both electrons go to one of the bonded atoms
Reagent to convert halogenoalkanes to alkenes
NaOH in ethanol
Explain the acidity of phenol
• lone pair on the oxygen overlaps with the pi system on the ring • hydrogen lost more easily which forms a phenoxide ion
What is the test to distinguish between phenols and carboxylic acids?
Na2CO3 —> phenol doesn’t react, carbox does
How are chloroalkanes formed from alcohols?
• HCl and anhydrous ZnCl2 OR PCl3 —> nucleophilic substitution
How are bromoalkanes formed from alcohols?
• KBr and conc H2SO4
Reaction of alcohols with ethanoyl chloride
• addition elimination reaction that produces esters and HCl
Observations when phenol is reacted with bromine
• orange bromine water is decolourise • white ppt of tribromophenol