17: Hydroxy Compounds

Question 1

Synthesis of Alcohols

Hydration of Alkenes

Answer 1

Laboratory Method
R&C:
Step 1: conc. H2SO4, cold
Step 2: H2O, heat
Mechanism: EA + Hydrolysis

Industrial Method
R&C:
H2O(g) with conc. H3PO4 as catalyst, SiO2, 70 atm, 300℃
Mechanism: EA

Question 2

Synthesis of Alcohols

Mild [O] of Alkenes

Answer 2

R&C: KMnO4 (aq), NaOH, cold

Question 3

Synthesis of Alcohols

Alkaline Hydrolysis of RX

Answer 3

R&C: NaOH(aq)/ KOH (aq), heat under reflex

Mechanism: Nucleohphilic Substitution

Question 4

Synthesis of Alcohols

[R] of Aldehydes, Ketones & RCOOH

Answer 4

R&C:
1. LiAlH4 in dry ether
2. NaBH4 in methanol (for Carbonyls only)
3. H2, Ni, heat

Question 5

Reducing Agents

Mechanisms of LiAlH₄ & NaBH₄

Answer 5

Provide a source of hydride ions ie. H^-

Question 6

Reactions of Alcohols

Acid-metal ie. Redox to form Alkoxide Ion

Answer 6

R&C: Na/ K, room temp.

Observations: Effervescence of H2(g) that extinguishes a lighted splint with a ‘pop’ sound

Mole ratio of ROH: H = 2:1

Question 7

Reactions of Alcohols

Condensation with RCOOH ie. Esterification to form Esters

Answer 7

R&C: RCOOH, conc. H2SO4 as catalyst, heat under reflux

1. H2SO4 provides H+ which catalyses reaction
2. Slow & reversible reaction –> System reaches equilibrium in a few hours

Question 8

Reactions of Alcohols

Condensation with Acyl Halides ie. Acylation to form Esters

Answer 8

R&C: Anhydrous RCOX, room temp.

Observations: Steamy white fumes of HX(g) which turn damp blue litmus paper red

Anhydrous condition needed as RCOCl hydrolyse in H2O

Question 9

KIV

Reactions of Alcohols

Nucleophilic Substitution to form RX

Answer 9

R&C:
1. Dry/ conc. HX(g) where X = Cl, Br, I
2. Anhydrous PX3, heat where X = Cl, Br/ red P, I2
3. PCl5, room temp.
3. SOCl2, room temp.

Question 10

Reactions of Alcohols

Dehydration ie. removal of H2O to form Alkenes

Answer 10

R&C:
1. Excess, conc. H2SO4, heat
2. Al2O3(s), heat
3. H3PO4, heat

Question 11

Reactions of Alcohols

Controlled [O] to form Aldehydes

Answer 11

R&C: K2Cr2O7, H2SO4, heat with immediate distillation

Observations: Orange solution turns green

Only 1 ROH

Question 12

Reactions of Alcohols

Further [O] to form Ketones/ RCOOH

Answer 12

R&C: K2Cr2O7/ KMnO4, H2SO4, heat under reflux

Observations: Orange solution turns green/ Purple solution decolourises

Only 1/2 ROH

Question 13

Reactions of Alcohols

[O] → Iodoform Test

Answer 13

R&C: I2, NaOH, heat

Observations: Yellow ppt. of CHI3

Question 14

Reactions of Phenol

Halogenation

Answer 14

1. Br2 in CCl4 (mono-sub)
2. Br2(aq) (tri-sub)
   Observations: Orange Br2 decolourises. White fumes of HBr(g) seen. White ppt seen.

Question 15

Reactions of Phenol

Nitration

Answer 15

1. HNO3(aq), room temp. (mono-sub)
2. conc. HNO3, room temp. (tri-sub)

Question 16

Reactions of Phenol

Condensation → Acylation to form Phenyl Esters

Answer 16

R&C: Anhydrous RCOX, room temp.

Observations: Steamy white fumes of HX(g) evolved turns damp blue litmus paper red.

Question 17

Reactions of Phenol

Condensation → Formation of Phenoxide Ion + Acylation to form Esters

Answer 17

R&C:
Step 1: NaOH(aq), room temp.
Step 2: RCOX, room temp.

Question 18

Role of NaOH(aq)

Condensation → Formation of Phenoxide Ion + Acylation to form Esters

Answer 18

NaOH(aq) converts phenol into a phenoxide ion, a stronger nucleophile

Question 19

Reactions of Phenol

Acid-metal/ base ie. Redox

Answer 19

R&C:
1. Na, room temp.
2. NaOH(aq), room temp.
Observations: Phenol dissolves to give a colourless solution./ 2 immiscible layers formed when the other compound is insoluble in H2O

Question 20

Reactions of Phenol

Complexisation

Characteristic Distinguishing Test for Phenol

Answer 20

R&C: Neutral FeCl3

Observations: Violent complexisation/ colour seen

Question 21

Determining Acidity

Framework

Answer 21

1. Type of Substituents
2. Size of (-)ve charge
3. Stability of conjugate base (CB)
4. Acid strength

Question 22

Determining Acidity

e^--donating Groups (EDG)

Answer 22

1. EDG
2. (-)ve charge becomes bigger ie. intensified
3. CB less stable
4. Weaker acid

1. When comparing aliphatic compounds, remember most groups other than R groups are EWG
2. When comparing aromatic compounds, refer to DB to determine if groups attached directly to Benzene are ED/ EW

Question 23

Determining Acidity

e^--withdrawing Groups (EWG)

Answer 23

1. EWG
2. (-)ve charge becomes smaller ie. dispersed
3. CB more stable
4. Stronger acid