Hydroxyl compounds (Alcohols) Flashcards
Physical properties of hydroxyl compounds
Structure: Simple molecular structure, polar molecule
1. Higher BP than alkanes (hydrogen bond > idid)
2. BP increases down the group
3. Alcohols and phenols soluble in water (hydrogen bond between water and alcohol/phenols > hydrogen bond between water molecules + hydrogen bond between alcohol/phenol molecules)
4. Alcohols and phenols soluble in organic solvents ( idid between alcohols/phenol molecule and organic molecules > idid between organic molecules + hydrogen bond between alcohol molecules)
Synthesis of alcohols
- electrophilic addition of alkenes
- nucleophilic substitution of RX
- Reduction of aldehydes and ketones
- Reduction of carboxylic acid
Electrophilic addition of alkenes
cold concentrated H2SO4, followed by H2O, heat OR
steam H2O(g), concentrated H3PO4, 300 degrees, 70 atm
Nucleophilic substitution of halogenoalkanes
NaOH/KOH(aq), heat under reflux
Reduction of aldehydes and ketones
LiAlH4 in dry ether OR H2 gas, Ni catalyst, heat
Reduction of carboxylic acids
LiAlH4 in dry ether
Reactions of alcohols
- combustion
- redox
- condensation ( Nucleophilic Sub)
- Nucleophilic Sub to form RX
- Elimination to form alkene
- Oxidation
Redox
Na(s) as Na is slightly acidic
OH–> O-Na+
Condensation to form ester
(alcohol)
- carboxylic acid, concentrated H2SO4, heat under reflux
- acyl chloride, room temperature
alcohol acts as nucleophile
concentrated H2SO4 acts as catalyst and dehydrating agent
Reaction (2) favoured as milder conditions needed and reaction goes to completion
Elimination to form alkene (Synthesis of alkene)
excess concentrated H2SO4, 170 degrees
Nucleophilic substitution to form RX
- PCl5, room temperature
- PCl3, heat under reflux
- PBr3, heat under reflux
- PI3, heat under reflux
- SOCl2, heat under reflux
…
Oxidation of primary alcohol
(i) Oxidation of primary alcohol to aldehyde
K2Cr2O7, H2SO4(aq), heat with immediate distillation
(ii) Oxidation of primary alcohol to carboxylic acid
K2Cr2O7, H2SO4(aq), heat under reflux OR KMnO4, H2SO4(aq), heat under reflux
Why heat with immediate distillation to produce aldehyde?
- Aldehyde could further oxidise to carboxylic acid
- Distillation required to separate aldehyde from oxidising agent to prevent further oxidation to carboxylic acid
- Aldehyde has lower BP than alcohol and vaporises faster
Oxidation of secondary alcohol
Oxidation of secondary alcohol to ketone
K2Cr2O7, H2SO4(aq), heat under reflux OR KMnO4, H2SO4(aq), heat under reflux
Iodoform test
I2, NaOH(aq), heat
Observation: Yellow ppt of CHI3 formed, brown I2 decolourises
–> Step-down reaction