LECTURE NOTE SK025 (ORGANIC) KMKt

9) Two OH groups ☞ diol OH
OH
EXAMPLE:
HOCH2CH2OH 1,2–cyclopentanediol
1,2–ethanediol

OH OH

Cl
4–chloro–1–phenyl–1,5–hexanediol

10) If two or more –OH on the aromatic ring:
Benzene derivatives with two –OH groups are
name as benzenediol

OH OH
OH

OH
Benzene-1,2-diol

Benzene-1,4-diol 5-bromobenzene-1,3-diol

16

EXERCISE 1 :

Give the IUPAC names of the following compounds.

(a) Cl CH3
(c) CH3CH2C═C(Cl)CH2OH

OH OH
(d)

(b)

Br

OH (e) HO—(CH2)8—OH

8.2 LEARNING OUTCOMES

Physical properties:
a) Explain the physical properties:
(i) boiling point
(ii) solubility in water

BOILING POINT

❑ In liquid form, molecules of alcohol can form
hydrogen bond between OH group and also
van der Waals forces between alkyls group.

EXAMPLE:

Hydrogen bond

Van der Waals forces

❑ As molecular weight increase (size of molecule
increase), the strength of van der Waals forces
increase, thus the boiling point will increase.

EXAMPLE:

Compound Molecular weight Boiling Point
(gmol-1) (oC)
Ethanol (2C) 46 78
CH3CH2OH
1-butanol (4C) 74 118
CH3CH2CH2CH2OH

❑ When the number of −OH groups increases,
boiling point increases.

⮚ This is due to the formation of more hydrogen bonds
between alcohol molecules

Example: Boiling Point (oC)
198
Compound 97
1,2-ethanediol
HOCH2CH2OH

1-propanol
CH3CH2CH2OH

❑ Alcohols have higher boiling points than
alkanes of similar molecular weight.

⮚ alcohols form hydrogen bond between
molecules while alkanes only form weak
van der Waals forces between molecules.

❑ Hydrogen bond is stronger than van der
Waals forces.
Example:

Compound Molecular weight Boiling Point
(gmol-1) (oC)
Ethanol 46 78
CH3CH2OH
44 -42
Propane
CH3CH2CH3

❑ For compounds of comparable molecular
size, the stronger the intermolecular forces,
the higher the boiling point.

EXAMPLE: CH3OCH2CH3 , CH3CH2CH2OH

CH3CH2CH2CH3 , Dipole Hydrogen
London dipole bond
Force London Dipole dipole
Force London
Force

Increasing BOILING POINT

EXERCISE 3:

Rank the compounds in each group in order of
increasing boiling point.

(a)
OH
OH

Br

(b) (CH3)3COC(CH3)3 CH3(CH2)3O(CH2)3CH3
CH3(CH2)7OH

ANSWER :

(a)

ANSWER :

(b)

SOLUBILITY

Hydrogen Bonding

❑ ≤ 5 C: water soluble
• Capable of H bonding to H2O

❑ > 5 C: water insoluble
• Non polar (hydrophobic) alkyl portion
is too large to dissolve in H2O

❑ The alkyl group are hydrophobic and the
hydroxyl group are hydrophilic.

❑ As the size of alkyl group increases, the
hydrophobic area increases, thus
solubility decrease.

Hydrophilic area

R-CH2-OH

Hydrophobic area

hydrophobic hydrophilic

ALKYL (R) O
H

WATER SOLUBILITY OF ALCOHOLS (AT 25oC)

ALKYL SOLUBILITY

methyl miscible

ethyl miscible

propyl miscible

tert-butyl miscible

isobutyl 10.0%

butyl 9.1%

pentyl 2.7%
hexane–1,6–diol miscible

❑ For alcohols with comparable molecular
weight,
• solubility increase with increasing
number of –OH groups.

• able to form more hydrogen bonds
with H2O molecules.

EXAMPLE:

Solubility : HO(CH2)6OH > CH3(CH2)5OH

☞ two OH groups ☞ one OH group
☞ can form more

H bonding with water

EXAMPLE:

Compare the solubility in water for the following
compounds.

(a) CH3CH2CH2CH3 CH3CH2CH2OH

(b) Br
OH

(c) CH3CH2CH2CH2OH HO3CH2CH2OH

ANSWER :

(a) Ability to form hydrogen bonding with H2O:

CH3CH2CH2CH3 Can’t form hydrogen bond
an alkane with water
☞ Insoluble in water

CH3CH2CH2OH Can form hydrogen bond with
an alcohol water
☞ Soluble in water

ANSWER :

(b) Br
OH an alkyl halide

an alcohol NO

Ability to form YES insoluble
H bonding

with H2O:
Solubility in water Soluble

ANSWER :

(c) CH3CH2CH2CH2OH HO3CH2CH2OH

Solubility : HO3CH2CH2OH > CH3CH2CH2CH2OH

☞ two OH groups ☞ one OH group
☞ can form more

H bonding with water

PHYSICAL PROPERTIES OF PHENOLS

❑ Strongly influenced by hydroxy group (-OH)

❑ has higher melting point and boiling point
than alkanes, arenes and aryl halides of
comparable molecular size.

❑ slightly soluble in water but has higher
solubility than alkanes, arenes and aryl
halides of comparable molecular size.

8.3 LEARNING OUTCOMES

Preparation of alcohols
a) Explain the preparation of alcohol by:

i. Fermentation
ii. Hydration of alkenes
iii.Hydrolysis of haloalkanes
iv.Addition of Grignard reagents

reagents to carbonyl compounds

8.3 PREPARATION OF ALCOHOLS

Explain the Fermentation
preparation of
alcohol by A biological process of enzymatic

degradation of sugars by microorganisms

C6H12O6 yeast 2CH3CH2OH + 2CO2

Hydration of Alkenes

Hydrolysis of Haloalkanes

Reaction with NaOH
Reaction with H2O

Addition of Grignard reagents to
carbonyl compounds.

Preparation of 1° alcohol
Preparation of 2° alcohol
Preparation of 3° alcohol

PREPARATION OF ALCOHOLS

1) Fermentation

❑ A biological process of enzymatic
degradation of sugars by microorganisms

C6H12O6 yeast 2CH3CH2OH + 2CO2

glucose ethanol

2) Hydration of Alkenes
❑ Method for preparation of simple alcohol.
❑ Reactant : Alkene and water
❑ Condition : Catalyst (H2SO4)

RR H—OH H3O+ RR
CC +
R C CR
RR
H OH
alkene alcohol

H and OH added!

❑ Follow Markovnikov’s Rule

EXAMPLE: H2O OH

CH2═CCH2CH2CH2CH3 H2SO4 CH3CCH2CH2CH2CH3
CH3 CH3

2–methyl–1–hexene 2–methyl–2–hexanol

H2O CH3 OH
1–methylcyclopentanol
H2SO4

CH3

1–methylcyclopentene

3) Hydrolysis of haloalkanes
❑ Reactant: haloalkane and NaOH or H2O

R—X + OH– R—OH +

X– alcohol

EXAMPLE: Substitute X with OH

CH3CH2—Br + NaOH (aq) CH3CH2—OH + NaBr

10 haloalkane Strong Nucleophile ethanol

bromoethane (CH3)3C–OH + HCl

(CH3)3C–Cl + H2O 2–methyl–2–propanol

30 haloalkane weak Nu

2–chloro–2–methylpropane

4) Addition of Grignard reagent to carbonyl
compounds

❑ 1o, 2o & 3o alcohols can be prepared by
addition of Grignard reagent with carbonyl
compounds followed by hydrolysis.

O [1] R’’MgX, ether OH
[2] H3O+ R C H@R’
C
R H@R’ R”
1o, 2o or 3o alcohol
aldehyde or ketone

(a) Formation of 1o alcohols
(Grignard reagent + methanal)

R–MgX + H ether H OMgX
CO RC
δ– δ+
H δ+ δ– H

methanal

H3O+

H
R C OH

new C–C bond H

1o alcohol 43

EXAMPLE: O

CH3CH2CH2CH2MgCl + H—C—H

Grignard reagent formaldehyde

ether

H
CH3CH2CH2CH2C OMgCl

H
H3O+

H

CH3CH2CH2CH2 C OH
H

1–pentanol

(b) Formation of 2o alcohols

(Grignard reagent + aldehyde)

R ether R

R–MgX + CO R C OMgX
H
δ– δ+ H δ+ δ–

aldehyde

H3O+

R
R C OH

new C–C bond H

2o alcohol

EXAMPLE: O

CH3CH2–MgBr + H–C–CH3

Grignard reagent acetaldehyde

ether

OMgBr

CH3CH2 C CH3
H
H3O+

OH

CH3CH2 C CH3

H
2–butanol

(c) Formation of 3o alcohol
(Grignard reagent + ketone)

R–MgX + R ether R
CO R C OMgX
δ– δ+
R δ+ δ– R

ketones H3O+

R
R C OH

new C–C bond R

3o alcohol

EXAMPLE: O
CH3CH2CH2CH2–MgX
+ CH3–C–CH3
acetone

ether

CH3
CH3CH2CH2CH2 C OMgX

CH3
H3O+

CH3
CH3CH2CH2CH2 C OH

CH3
2–methyl–2–hexanol

O OH

[1] H–C–H , ether H C H

[2] H3O+ new C–C

R bond
1o alcohol

R–MgX O OH
[1] H–C–R’, ether
[2] H3O+ H C R’

new C–C

R bond
2o alcohol

O OH

[1] R’–C–R” , ether R’ C R”

[2] H3O+ R new C–C
bond
3o alcohol

❑ Sometimes, there are two or three possibilities
to prepare alcohol using Grignard reagent

EXAMPLE: preparation of 2–butanol

OH OH
CH3—C—CH2CH3 CH3—C—CH2CH3

H H

OO
CH3–MgCl + H–C–CH2CH3 CH3–C–H + CH3CH2–MgCl

8.4 LEARNING OUTCOMES

Chemical properties of alcohols
a) Explain the reactions of alcohol with reference to:

(i) reaction with sodium
(ii) esterification
(iii) dehydration
(iv) substitution reactions using HX, PX3, PCl5 or SOCl2
b) Explain the oxidation reactions with KMnO4/H+, Cr2O7/H+,
CrO3/H+ and PCC/CH2Cl2

c) Explain the identification tests to distinguish

classes of alcohols using Lucas reagent, i.e.

concentrated HCl/ZnCl2
d) Explain iodoform test, i.e. I2/OH- to identify

methyl carbinol CH3CH(OH).
d) Outline the synthesis of compounds

involving alcohols

8.4 CHEMICAL PROPERTIES OF ALCOHOLS

Chemical Reactions of Alcohol
Properties of
Reaction with sodium, Na
Alcohols Substitution Reaction HX, PX3, PX5, SOCl2
Esterification
Dehydration

Oxidation of Alcohols

Acidified solution of chromate
Acidified solution of permanganate
Pyridinium chlorochromate, PCC

Identification Test

Lucas Test

Iodoform Test

To identify methyl carbinol

TYPES OF REACTIONS OF
HYDROXY COMPOUNDS

1) Cleavage of bond between O and H in -OH
group (O-H bond is broken in R-O-H):

(a) Reaction with Na
(b) Esterification
(c) Oxidation

2) Cleavage of bond between C and O (C-OH
bond is broken in R-O-R):

(a) Dehydration
(b) Substitution reaction using :
HX, PX3, PX5 or SOCl2

(A) REACTION WITH SODIUM

❑ Reactant : alcohol and Na
❑ Product : sodium alkoxide and H2 gas

R—O—H + Na R—O– Na+ + ½ H2↑

sodium alkoxide

EXAMPLE: The alcohol acts
as an acid

CH3CH2OH + Na CH3CH2O–Na+ + ½H2↑

ethanol sodium ethoxide

(B) ESTERIFICATION

❑ Reactant : carboxylic acid and alcohol
❑ Condition : • Reflux

• Catalyst (H2SO4 or HCl)
❑ Product : ester and H2O

O H+ O
R—OH + R C OH
R C OR + H2O
∆ ester
57

EXAMPLE:

O O
H+
CH3COH + CH3CH2OH
CH3COCH2CH3 + H2O
acetic acid ethanol
∆

ethyl acetate

O H+ O + H2O
COH + CH3OH COCH3
∆
benzoic acid methanol
methyl benzoate

(C) OXIDATION

❑ Oxidizing agent:
• Acidified solution of chromate
(Na2Cr2O7, K2Cr2O7, CrO3)
• Acidified solution of permanganate
(KMnO4)
• Pyridinium chlorochromate (PCC) in CH2Cl2

❑ Oxidation product depends on the class of
alcohol used and types of oxidizing agent.

Oxidation of 1o alcohol

❑ 1o alcohols are oxidized to aldehydes or
carboxylic acids, depending on the
reagent:

Oxidising Agent Product
aldehyde
PCC in CH2Cl2
(mild condition)

Hot acidified KMnO4 , carboxylic acid
Na2Cr2O7, K2Cr2O7, or CrO3
(harsher condition)

OH O O
[O]
RCH RCH
R C OH or
H aldehyde
carboxylic acid
1o alcohol

EXAMPLE: O

CH3CH2CH2CH2OH Na2Cr2O7, H+ CH3CH2CH2C OH
∆
1–butanol butanoic acid

CH2OH O

PCC CH
CH2Cl2

cyclohexyl methanol cyclohexanal

Oxidation of 2o alcohol

❑ 2o alcohol is oxidised to ketone

OH [O] O

R CHR RC R
2o alcohol ketone

EXAMPLE: OH O

KMnO4 , H+

∆

cyclohexanol cyclohexanone

OH PCC O
C2H–3pCrHoCpaHn3ol CH3C—CH3
CH2Cl2 propanone

Oxidation of 3o alcohol

❑ 3o alcohol does not undergo oxidation
under normal condition.

⮚ have no C–H bond on the C bearing the
OH group.

OH [O] no oxidation
RCR

R
3o alcohol

SUMMARY

Class of alcohol Reaction with Product

1o KMnO4 /Na2Cr2O7 / Carboxylic acid
K2Cr2O7 / CrO3

PCC Aldehyde

2o KMnO4 /Na2Cr2O7 / Ketone
K2Cr2O7 / CrO3

PCC Ketone

KMnO4 /Na2Cr2O7 /

3o K2Cr2O7 / CrO3 No reaction

PCC 64