Alcohols & Phenols Flashcards
Why do alcohol and phenol have higher boiling points?
Hydrogen bonding is present between molecules of alcohol and phenols, thus more energy is required to overcome stronger hydrogen bonding.
Preparation of Alcohols: EA from Alkenes
Steam, H3PO4 catalyst, high temp & pressure
OR
Cold conc. H2SO4, water heat.
Preparation of Alcohols: NS from RX
NaOH (aq), heat under reflux
Preparation of Alcohols: Reduction
LiAlH4 in dry ether
OR
NaBH4 in methanol, followed by H2O
OR
H2 Ni catalyst, heat.
Aldehydes > Pri alcohols
Ketones > Sec alcohols
Preparation of Alcohols: Reductions from Carboxylic Acids
LiAlH4 in dry ether, followed by H2O
Reactions of Alcohols: Elimination of H2O
Excess conc H2SO4, 170 D.C
OR
Al2O3 catalyst, 350 D.C
Reactions of Alcohols: NS wtih PX3 or PCL5
dry PCL5(s), room temp
OR
dry PX3, heat
Note: PBr3 and PI3 are made in situ, via reaction of P4 and Br2/I2
Reactions of Alcohols: NS with SOCl2
Dry SOCl2 (l), heat.
Forms: RX, SO2, and HCl
Reaction of Alcohols: NS with HX
Dry HX or Conc HX
Reaction of 1’ alcohols: Oxidation to Aldehyde
Acidified Kr2Cr2O7 (aq), distill immediately
Reactions of 1’ Alcohols: Oxidation to Carboxylic acid
Acidified Kr2Cr2O7 (aq), heat under reflux
Or
Acidified KMnO4(aq), heat under reflux
Reactions of 2’ Alcohols: Oxidation to Ketone
Acidified Kr2Cr2O7 (aq), heat under reflux
Or
Acidified KMnO4(aq), heat under reflux
Reactions of Alcohols: Condensation/ NS with RCOOH/RCOCl
RCOOH, conc H2SO4, heat under reflux
OR
ROCl, room temp
Note: H2SO4 has two functions
- acts as a catalyst by making RCOOH a better leaving group
- Acts as a dehydrating agent, moving equilibrium to the right, forming more ester.
Introduction to Phenol: Why do Phenols (1/2) not undergo NS but undergo ES (i/ii)
- C-O bond is stronger in phenol than in alcohol
- P-P orbital overlap results in delocalisation of LP of electrons on oxygen atom into the benzene ring. Resulting in a formation of C-O partial double bond.
i. P-P orbital overlap results in delocalisation of LP of electrons on oxygen atom into the benzene ring. This makes the benzene ring more electron rich.
ii. Thus, -OH group is strongly activating and hence phenol is more susceptible to ES.
Reaction of Phenol: Condensation/ Reaction with Acyl Chlorides
- Phenol in NaOH (aq)
- ROCl, room temp
Note: Phenol reacts with NaOH to form a stronger nucleophile, Phenoxide ion.
Intro to Phenol: Why does Phenol not react with Carboxylic acid?
The p–p orbital overlap results in delocalisation of the lone pair of electrons on O into the benzene ring and hence the lone pair is less available to attack the δ+ C in the carboxylic acid.
In acyl chloride, the C in the >C=O group is highly electron-deficient than that in the carboxylic acid as it is directly bonded to two electronegative atoms, O and Cl, making it more susceptible to attack by a nucleophile to from ester.
Reactions of Phenol: Iodoform test
alkaline I2 (aq), heat
OR
I2, NaOH(aq) and heat
Observations: Brown I2 decolourises and a pale yellow ppt. of CHI3 with a characteristic ‘antiseptic’ smell is formed upon cooling.
Note: Only Ethanol and Secondary Alcohols give positive Iodoform test
Reactions of Phenol: Ferric Phenoxide test
Add neutral FeCl3(aq) to the sample in a test-tube.
Obs: A violet colouration will be observed.
Reactions of Phenol: ES of Br2 (aq)
Add Br2(aq) to the sample in a test-tube.
Obs: Orange Br2(aq) decolourises.
White ppt. of 2,4,6-tribromophenol will be formed upon adding excess Br2.
Acid Behaviour of Alcohols and Phenols
Alcohols and phenols are weak acids which ionise partially in aqueous solution.
The strength of acids depends on the relative stability of the resulting anion (conjugate base) formed.
Stability of the resulting anion RO– formed is affected by:
(i) Electron-donating group intensifies the negative charge, thereby destabilising the RO– ion.
(ii) Electron-withdrawing group disperses the negative charge, thereby stabilising the RO– ion.
Alcohol vs Carboxylic acid vs Phenol
All reacts with Na(s) to give H2(g), Redox reaction
Only RCOOH and Phenol reacts with NaOH(aq), Acid base reaction
Only RCOOH reacts with Na2CO3(aq), Acid Carbonate reaction
