Summary – Hydroxy Compounds Reactions
No Reactants Reagents & Conditions Products Type of Reaction
HYDROXY COMPOUNDS (general formula for alcohols: CnH2n+2O)
33 CH3CH2OH 2CO2 + 3H2O Complete Combustion
34 CH3CH2OH CH2CH2O–Na+ + ½H2(g) Redox reaction
* Alcohols are weaker acids
35 CH3CH2OH No reaction than water and thus cannot
undergo acid –base
reaction with strong bases.
dry PCl5, room temp. Nucleophilic Substitution
31 CH3CH2OH CH3CH2Cl * OH group in RCO2H also
or, dry PCl3, heat
reacts while OH group in
or, dry SOCl2, heat
phenol does not.
* anhydrous conditions r’qd
dry as PCl5/ PX3/SOCl2 reacts
CH3CH2OH CH3CH2Br vigorously with water.
Nucleophilic Substitution
32 * only alcohols react in this
where X: Cl, Br nucleophilic substitution.
* Tertiary alcohol is more
reactive than primary
Or alcohol. Hence, heating or
CH3CH2OH CH3CH2Cl HX(g), catalyst is not required (i.e.
primary alcohol heat milder condition suffice)
CH3CH2OH
primary alcohol
CH3CH2Br
Mild Oxidation
* Stronger oxidising agent,
CH3CH2OH K2Cr2O7(aq) in H2SO4(aq)
36 KMnO4, cannot be used to
primary alcohol
Heat with immediate distillation form aldehyde (RCO2H is
formed instead) even under
distil condition.
K2Cr2O7(aq) (or KMnO4(aq))
in H2SO4(aq) Oxidation of primary alcohol
37 R–CH2OH
primary alcohol
K2Cr2O7(aq) in H2SO4(aq) *HCO2H and HOOC-COOH will
CH3OH HCO2H (methanoic acid)
be further oxidised to CO2
methanol
and H2O if a stronger
oxidising agent such as
KMnO4(aq) in H2SO4(aq) KMnO4 is used.
CH3OH CO2 + H2O
methanol
K2Cr2O7(aq) in H2SO4(aq)
KMnO4(aq) in H2SO4(aq)
2CO2 + 3H2O
HYDROXY COMPOUNDS (general formula for alcohols: CnH2n+2O) (CONTINUED)
No Reactants Reagents & Conditions Products Type of Reaction
K2Cr2O7(aq) (or KMnO4(aq))
in H2SO4(aq)
38 Oxidation of secondary
alcohols
K2Cr2O7(aq) (or KMnO4(aq))
in H2SO4(aq)
39 No reaction
40 CH3CH2OH Condensation or Nucleophilic
alcohol Acyl Substitution
41 CH3CH2OH Condensation or Nucleophilic
alcohol Acyl Substitution
11
heat
Elimination
Al2O3, high temperature) * Apply Zaitsev’s Rule
H2O is eliminated
across 2 adjacent C.
Positive triiodomethane
/iodoform Test
42
* Test for the presence of
butan–2–ol
ethanal / ketones
ethanol ( + 4I2 + 6NaOH ) ( + 5NaI + 5H 2O)
43 Redox reaction
44 Acid–Base Reaction
45 No reaction
46 No reaction
Condensation or Nucleophilic
Acyl Substitution
* Due to p-p orbital overlap,
lone pair on O is delocalised
into the benzene ring and
47
hence phenol is a poor
nucleophile. It is first reacted
with NaOH(aq) to form
phenoxide which is a better
nucleophile.
No Reactants Reagents & Conditions Products Type of Reaction
Electrophilic Substitution
* OH group is a strongly
ring-activating group as
48 the p–p orbital overlap
results in delocalisation of
lower b.p. Why? the lone pair of electrons on
O atom into the benzene
ring, making the benzene
ring more electron–rich,
and more susceptible
towards electrophilic
substitution.
* stronger electrophile
+
NO2 (generated by conc.
H2SO4 catalyst) or Br+
(generated by Br2 and FeBr3
cataylst) and heating are
not required for
electrophilic substitution
of phenol (i.e. milder
acidic solution condition will suffice).
+ 3Br2
of HBr(aq) Note: HNO3 is a weaker
+
electrophile than NO2 which
has a full positive charge.
+ 3Cl2
acidic solution
of HCl(aq)
* OH group is a stronger
+ 3Br2 electron donating and
3-methylphenol : Br2
ring–activating group
1 : 3
than CH3.
Hence, the effect of OH
dominates over CH3 and
directs the electrophile to
the 2–, 4– AND 6–positions
relative to OH.
+ 2Br2 2-methylphenol : Br2
1 : 2
SOME COMMON IDENTIFICATION TESTS
Functional Group Reagent and Conditions Observations
1. Primary & Secondary
Alcohols *Test 1: {Oxidation}
E.g. CH3CH2CH2CH2OH Add *H2SO4(aq) followed by a Purple KMnO4 decolourises.
few drops of KMnO4(aq) and
heat.
and Test 2: {Oxidation}
Add H2SO4(aq) followed by a few Orange K2Cr2O7(aq) turns green.
drops of K2Cr2O7(aq) and heat.
Test 3: {Nucleophilic Substitution}
Add dry PCl5(s). {Test-tube and Dense white fumes of HCl
reagents used must be dry} liberated.
2. Tertiary Alcohols Test 1: {Nucleophilic Substitution}
E.g. Add dry PCl5(s). {Test-tube and Dense white fumes of HCl
reagents used must be dry} liberated.
3. Alcohols with
structure: Test 1: {PositiveTriiodomethane /
Iodoform Test}
Add aqueous I2, aqueous NaOH Pale yellow ppt. of CHI3 with
and heat. decolourisation of brown I2(aq).
E.g.
Test 1: {Electrophilic Substitution} Orange Br2 decolourises initially.
4. Phenol, White ppt. is formed upon adding
Add excess Br2(aq).
excess Br2.
Test 2: Add neutral FeCl3(aq). Violet colouration is observed.
E.g.
