4.3 - Alcohols and Phenols Flashcards
What is the test for alcohols
- add Cr2O72-/H+
If alcohol is present the solution will go from orange to green
What are the different ways to form an alcohol
- Nucleophilic substitution of a halogenoalkane
- Reduction of carbonyls and carboxylic acid
What is the reaction for the formation of alcohols from halogenoalkanes
- nucleophilic substitution
- need a halogenoalkane and aqueous alkali
- reflux
eg. bromoethane + sodium hydroxide = ethanol + sodium bromide
Must know the mechanism
- curly arrows
- charges
- intermediate
What is the reaction to form alcohols from the reduction of carbonyls
- Aldehydes > primary alcohols
- reduced with NaBH4 (aq)
eg. CH3OH + 2[H] > CH3CH2OH - Ketone > secondary alcohols
- reduced with NABH4
eg. CH3COCH3 + [H] > CH3CH(OH)CH3
What is the reaction to form alcohols from a carboxylic acid
Carboxylic acid > primary alcohol
- reduced with LiAlH4 dissolved in ethoxyethane
eg. CH3COOH + 4[H] > CH3CH2OH
How can the rate of hydrolysis be measured in alcohols
The rate of hydrolysis can be ,ensured using AgNO3 as a precipitate of silver halide will form
AgCl - white precipitate
AgBr - cream precipitate
AgI - yellow precipitate
Iodoalkanes hydrolyse the fastest as the C-I bond is the weakest so breaks the quickest
C-I < C-Br < C-Cl
C-Cl is the strongest bond as it hydrolyses in the slowest time
What are the reactions of alcohols to form halogenoalkanes
Alcohols > halogenoalkanes with hydrogen halides
Very slow reversible reaction that gives a poor yield
- Chlorination
- pass HCl (g) into an alcohol with a zinc chloride catalyst
eg. CH3CH2OH + HCl > CH3CH2Cl + H2O - Bromination
- heat with KBr and 50% H2SO4
KBr + H2SO4 > HBr which is then reacted
eg. CH3CH2OH + KBR + H2SO4 > CH3CH2BR + KHSO4 + H2O - Iodination
- heat and reflux alcohol with excess HCl
eg. CH3CH2OH + HI > CH3CH2I + H2O
What is the reaction of alcohols to form esters
- acid chlorides COCl
A rapid reaction forms misty fumes of HCl, has a good yield but very expensive - condensation reaction (HCl removed)
CH3CH2CH(CH3)OH + CH3COCl > CH3CH2C(CH3)OC=OCH3 + HCl
What is the reaction of an alcohol with a carboxylic acid
- poor yield as reversible reaction will eventually reach equilibrium
- increase yield by using concentrated H2SO4 and heat with reflux
eg. CH3CH2OH (aq) + CH3COOH (aq) 🔛 CH3CH2COOCH3 (aq) + H2O (l)
To separate
- distil products at boiling point of the ester to remove impurities
- add sodium hydrogencarbonate until fizzing to remove unreacted acid
- use separating funnel to separate liquid organic and aqueous layers
- add anhydrous calcium chloride
- redistill the product
What is the test for a phenol
- add iron (iii) chloride (aq)
If phenol is present the solution will go from orange to purple
What is phenol
- the simplest member of the family of compounds that contain an OH group attached directly to a benzene ring
The delocalised electron ring from benzene and the lone pair of electrons on the oxygen atom cause phenol to be more reactive than benzene and more acidic than alcohols
What are the physical properties of phenol
- phenol is a white crystalline solid at room temperature
- phenol is able to form hydrogen bonds due to OH group and has a higher melting and boiling point than similarly sized aromatic compounds
- phenol is moderately soluble in water due to the formation of H bonds with H2O but less soluble than alcohols as it only has one lone pair of electrons
Acidity
- molecules with an OH group are weakly acidic due to the ability for H+ ions to be lost, alcohols are so weak it is ignored however phenol does not do this. A phenoxide ion is more stable as it only has one lone pair of electrons and is more likely to form than an alcohol. Phenol is very weakly acid so little dissociation occurs as the oxygen atom is electronegative and draws electrons into the ring attracting H+ ions and molecular acid reforms
What are the acid reactions of phenol
- With NaOH (alkali)
Phenol + NaOH > sodium phenoxide ion + H2O - With Na (metal)
2 phenol + 2 Na > 2 sodium phenoxide ions + H2
(Very slow reaction effervescence seen but Na must be warmed to molten) - With Na2CO3/ NaHCO3
- no reaction as it’s not acidic enough to produce CO2 with CO3 2- or HCO3-
- can be used to confirm the presence of phenol with other tests
How do the reactions of phenol occur
The OH group activates the ring by increasing electron density, this is because the lone pair of electrons on the oxygen in phenol is drawn into the benzene ring, leaving it susceptible to electrophilic attack
The OH group has a directing effect and activates 2,4 on the benzene ring so incoming groups are substituted onto carbon 2 or 4
- when using methyl phenol groups attach to 4,6 position
What is the reaction of phenol with bromine (Br2)
- can identify phenols as forms a white precipitate that smells of antiseptic
- bromine water goes from orange to colourless
C6H5OH + Br2 > C6H4OHBr + HBr
If excess
C6H5OH + 3Br2 > C6H2OHBr3 + 3HBr
- does not need a halogen carrier because of the OH group
