Alcohols & Phenols

Question 1

Why do alcohol and phenol have higher boiling points?

Answer 1

Hydrogen bonding is present between molecules of alcohol and phenols, thus more energy is required to overcome stronger hydrogen bonding.

Question 2

Preparation of Alcohols: EA from Alkenes

Answer 2

Steam, H3PO4 catalyst, high temp & pressure
OR
Cold conc. H2SO4, water heat.

Question 3

Preparation of Alcohols: NS from RX

Answer 3

NaOH (aq), heat under reflux

Question 4

Preparation of Alcohols: Reduction

Answer 4

LiAlH4 in dry ether
OR
NaBH4 in methanol, followed by H2O
OR
H2 Ni catalyst, heat.

Aldehydes > Pri alcohols
Ketones > Sec alcohols

Question 5

Preparation of Alcohols: Reductions from Carboxylic Acids

Answer 5

LiAlH4 in dry ether, followed by H2O

Question 6

Reactions of Alcohols: Elimination of H2O

Answer 6

Excess conc H2SO4, 170 D.C
OR
Al2O3 catalyst, 350 D.C

Question 7

Reactions of Alcohols: NS wtih PX3 or PCL5

Answer 7

dry PCL5(s), room temp
OR
dry PX3, heat

Note: PBr3 and PI3 are made in situ, via reaction of P4 and Br2/I2

Question 8

Reactions of Alcohols: NS with SOCl2

Answer 8

Dry SOCl2 (l), heat.

Forms: RX, SO2, and HCl

Question 9

Reaction of Alcohols: NS with HX

Answer 9

Dry HX or Conc HX

Question 10

Reaction of 1’ alcohols: Oxidation to Aldehyde

Answer 10

Acidified Kr2Cr2O7 (aq), distill immediately

Question 11

Reactions of 1’ Alcohols: Oxidation to Carboxylic acid

Answer 11

Acidified Kr2Cr2O7 (aq), heat under reflux
Or
Acidified KMnO4(aq), heat under reflux

Question 12

Reactions of 2’ Alcohols: Oxidation to Ketone

Answer 12

Acidified Kr2Cr2O7 (aq), heat under reflux
Or
Acidified KMnO4(aq), heat under reflux

Question 13

Reactions of Alcohols: Condensation/ NS with RCOOH/RCOCl

Answer 13

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.

Question 14

Introduction to Phenol: Why do Phenols (1/2) not undergo NS but undergo ES (i/ii)

Answer 14

1. C-O bond is stronger in phenol than in alcohol
2. 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.

Question 15

Reaction of Phenol: Condensation/ Reaction with Acyl Chlorides

Answer 15

1. Phenol in NaOH (aq)
2. ROCl, room temp

Note: Phenol reacts with NaOH to form a stronger nucleophile, Phenoxide ion.

Question 16

Intro to Phenol: Why does Phenol not react with Carboxylic acid?

Answer 16

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.

Question 17

Reactions of Phenol: Iodoform test

Answer 17

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

Question 18

Reactions of Phenol: Ferric Phenoxide test

Answer 18

Add neutral FeCl3(aq) to the sample in a test-tube.

Obs: A violet colouration will be observed.

Question 19

Reactions of Phenol: ES of Br2 (aq)

Answer 19

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.

Question 20

Acid Behaviour of Alcohols and Phenols

Answer 20

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.

Question 21

Alcohol vs Carboxylic acid vs Phenol

Answer 21

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