2. SUBTOPICS
Nomenclature of alcohols, phenols.
Classification of alcohols.
Physical properties of alcohols:
- Physical state
- Boiling points
- Solubility of alcohols in water
Acidity of alcohols and phenols
Reactions of alcohols:
- Reaction with sodium
- Oxidation
- Esterification
- Halogenation and haloform reactions
- Dehydration
- Formation of ether (Williamson ether synthesis)
3. Reactions of phenols:
- Reaction with sodium
- Esterification
- Halogenation of the ring
- Nitration of the ring
Tests to distinguish classes of alcohols:
i) Lucas test
ii) Oxidation
Haloform test to identify methyl alcohol group
- Iodoform
- Bromoform
Uses of alcohols and phenols.
4. ALCOHOLS
Alcohols: Organic compounds containing
hydroxyl (-OH) functional groups.
R OH
Phenols: Compounds with hydroxyl group bonded
directly to an aromatic (benzene) ring.
OH
6. IUPAC RULES
1. Select the longest continuous chain of carbon atoms
containing the hydroxyl group.
2. Number the carbon atoms in this chain so that the
one bonded to the –OH group has the lowest
possible number.
3. Form the parent alcohol name by replacing the final
–e of the corresponding alkane name by –ol. When
isomers are possible, locate the position of the –OH
by placing the number (hyphenated) of the carbon
atom to which the –OH is bonded immediately before
the parent alcohol name.
4. Name each alkyl branch chain (or other group) and
designate its position by number.
7. This is the longest continuous chain that
contains an hydroxyl group.
Select this chain as the parent compound.
8. 4
3
2 1
This end of the chain is closest to the
OH. Begin numbering here.
13. NOMENCLATURE OF CYCLIC
ALCOHOLS
Using the prefix cyclo-
The hydroxyl group is assumed to be on C1.
IUPAC name:
new IUPAC name:
H
HO CH2CH3
5 6 1
4 3 2
Br
OH
H
trans-2-bromocyclohexanol
trans-2-bromocyclohexan-1-ol
1
3 2
1-ethylcyclopropanol
1-ethylcyclopropan-1-ol
14. NOMENCLATURE OF ALCOHOLS
CONTAINING TWO DIFFERENT
FUNCTIONAL GROUPS
Alcohol containing double and triple bonds:
- use the –ol suffix after the alkene or alkyne name.
The alcohol functional group takes precedence over
double and triple bonds, so the chain is numbered in
order to give the lowest possible number to the carbon
atom bonded to the hydroxyl group.
The position of the –OH group is given by putting its
number before the –ol suffix.
Numbers for the multiple bonds were once given early in
the name.
15. EXAMPLE
4 3 2 1
CH2 CH CH2 CH CH3
OH
5
1) Longest carbon chain that contains –OH group
- 5 carbon
2) Position of –OH group
- Carbon-2
3) Position of C=C
- Carbon-4
COMPLETE NAME = 4-penten-2-ol
16. Some consideration:
- OH functional group is named as a hydroxy
substituent when it appears on a structure with a
higher priority functional group such as acids, esters,
aldehydes and ketones.
- Examples:
OH
4 3 2 1
OH
1 2
3 45
6 O
CH3 CH
O
CH2 C
OH
3-hydroxybutanoic acid 2-hydroxycyclohexanone
17. MAIN GROUPS
Acids
Esters
Aldehydes
Ketones
Alcohols
Amines
Alkenes
Alkynes
Alkanes
Ethers
Halides
decreasing priority
18. NOMENCLATURE OF DIOLS
Alcohols with two –OH groups are called diols or
glycols.
Naming of diols is like other alcohols except that the
suffix diol is used and two numbers are needed to
tell where the two hydroxyl groups are located.
OH
3CH 2 1 3 CH
CH2 OH
OH
OH
5
propane-1,2-diol trans-cyclopentane-1,2-diol
IUPAC name
1
3 2
4
19. NOMENCLATURE OF
PHENOLS
The terms ortho (1,2-disubstituted), meta (1,3-
disubstituted) and para (1,4-disubstituted) are often
used in the common names.
OH
Br
O2N OH
OH
CH3CH2
IUPAC name:
common name:
2-bromophenol
ortho-bromophenol
3-nitrophenol
meta-nitrophenol
4-ethylphenol
para-ethylphenol
20. Phenols may be monohydric, dihydric or
trihydric according to the number of hydroxyl
groups present in the benzene ring.
OH
OH
OH
OH
OH
OH
OH
benzene-1,3-diol benzene-1,4-diol benzene-1,2,3-triol
21. CLASSIFICATION
According to the type of carbinol carbon atom (C bonded
to the –OH group).
C OH
Classes:
i) Primary alcohol
- -OH group attached to a primary carbon atom
ii) Secondary alcohol
- -OH group attached to a secondary carbon atom
iii) Tertiary alcohol
- -OH group attached to a tertiary carbon atom
22. TTYYPPEE SSTTRRUUCCTTUURREE EEXXAAMMPPLLEESS
i) Primary (1°)
ii) Secondary (2°)
iii) Tertiary (3°)
R C
H
OH
H
R C
H
OH
R'
R C
R''
OH
R'
CH3
CH3CH2-OH CH3CHCH2
OH
ethanol 2-methyl-1-propanol
OH
H3C CH
CH2CH3
OH
2-butanol cyclohexanol
CH3
C
OH
CH3
H3C
2-methyl-2-propanol
23. Polyhydroxy Alcohols
• Alcohols that contain more than one OH group
attached to different carbons are called polyhydroxy
alcohols.
• Monohydroxy: one OH group per molecule.
• Dihydroxy: two OH groups per molecule.
• Trihydroxy: three OH groups per molecule.
24.
25. PPHHYYSSIICCAALL PPRROOPPEERRTTIIEESS
PHYSICAL STATES OF ALCOHOLS
- simple aliphatic alcohols and lower aromatic
alcohols (such as phenylmethanol, C6H5CH2OH)
→ liquids at room temperature.
- highly branched alcohols and alcohols with twelve
or more carbon atoms → solids.
26. BOILING POINTS
- The boiling points of alcohols are higher than those of
alkanes and chloroalkanes of similar relative molecular mass.
- For example:
C2H5OH CH3CH2CH3 CH3Cl
Relative molecular mass: 46 44 50.5
Boiling point: 78°C -42°C -24°C
- Reason:
intermolecular hydrogen bonds exist between the –OH
groups in the alcohol molecules.
R
δ-
O
H
δ+
H R
O
Ar
δ- δ+
O
H
H Ar
O
δ-
δ-
hydrogen bonding hydrogen bonding
- Branched chain alcohols boils at a lower temperature (more
volatile) than the straight chain alcohols with the same number of
carbon atoms.
27. SOLUBILITY OF ALCOHOLS IN WATER
i) alcohols with short carbon chains (such as methanol,
ethanol, and propanol) dissolve in water.
- when alcohols dissolve in water, hydrogen bonds are formed
between the –OH group of the alcohol molecule and the –OH
group of the water molecule.
ii) the solubility of alcohols in water decreases sharply with the
increasing length of the carbon chain. Higher alcohols are
insoluble in water.
- alcohol contains a polar end (-OH group) called ‘hydrophilic’
and a non-polar end (the alkyl group) called ‘hydrophobic’.
- the water solubility decreases as the alkyl group becomes
larger.
28. iii) alcohols with more than one hydroxyl group (polyhydroxy
alcohols) are more soluble than monohydroxy alcohols with
the same number of carbon atoms. This is because they
can form more hydrogen bonds with water molecule.
iv) branched hydrocarbon increases the solubility of alcohol in
water.
- reason: branched hydrocarbon cause the hydrophobic
region becomes compact so decrease surface area. As the
surface area of the non-polar part in the molecule
decreases, the solubility increases.
* Phenol is sparingly soluble (9.3%) because of its compact
shape and the particularly strong hydrogen bonds formed
between phenolic –OH groups and water molecules.
29. AACCIIDDIITTYY OOFF AALLCCOOHHOOLLSS AANNDD PPHHEENNOOLLSS
Alcohol is weakly acidic.
In aqueous solution, alcohol will donated its proton to
water molecule to give an alkoxide ion (R-O-).
R-OH + H2O R-O- + H3O+ Ka = ~ 10-16 to 10-18
alkoxide ion
Example
CH3CH2-OH + H2O CH3CH2-O- + H3O+
The acid-dissociation constant, Ka, of an alcohol is defined
by the equilibrium
R-OH + H2O Ka R-O- + H3O+
Ka = [H3O+] [RO-]
[ROH]
pKa = - log (Ka)
* More smaller the pKa
value, the alcohol is
more acidic
30. Acidity OF PHENOLS
Phenol is a stronger acid than alcohols and water.
R-OH + H2O R-O- + H3O+ Ka = ~ 10-16 to 10-18
alcohol alkoxide ion
OH H2O O- H3O+
phenol phenoxide ion
Ka = 1.2 x 10-10
H2O + H2O HO- + H3O+ Ka = 1.8 x 10-16
hydroxide ion
31. Phenol is more acidic than alcohols by considering
the resonance effect.
i) The alkoxide ion (RO-)
- the negative charge is confined to the oxygen and
is not spread over the alkyl group.
- this makes the RO- ion less stable and more
susceptible to attack by positive ions such as H+
ions.
32. ii) The phenoxide ion
- one of the lone pairs of electrons on the oxygen atom is
delocalised into the benzene ring.
- the phenoxide ion is more stable than the alkoxide ion
because the negative charge is not confined to the
oxygen atom but delocalised into the benzene ring.
- the phenoxide ion is resonance stabilised by the
benzene ring and this decreases the tendency for the
phenoxide ion to react with H3O+.
O O O O
33. EFFECTS OF Acidity
The acidity decreases as the substitution on the alkyl group increase.
- Reason: a more highly substituted alkyl group inhibits solvation of
the alkoxide ion and drives the dissociation equilibrium to the left.
- For example: methanol is more acidic than t-butyl alcohol.
The present of electron-withdrawing atoms enhances the acidity of
alcohols.
- Reason: the electron withdrawing atom helps to stabilize the
alkoxide ion.
- For example: 2-chloroethanol is more acidic than ethanol because
the electron-withdrawing chlorine atom helps to stabilize the 2-
chloroethoxide ion.
- alcohol with more than one electron withdrawing atoms are more
acidic. For example, 2,2,-dichloroethanol is more acidic than 2-
chloroethanol.
- Example of electron-withdrawing atom/groups:
Halogen atoms and NO2.
34. RREEAACCTTIIOONNSS OOFF AALLCCOOHHOOLLSS
Reaction with sodium
Oxidation
Esterification
Halogenation and haloform reactions
Dehydration
Formation of ether (Williamson ether
synthesis)
35. Reaction with sodium
Alcohols reacts with Na at room temperature to
form salts (sodium alkoxides) and hydrogen.
2R-O-H + 2Na → 2R-O- Na+ + H2
For example:
CH3CH2OH + Na → CH3CH2O-Na+ + 1/2H2
alcohol sodium ethoxide
Reactivity of alcohols towards the reactions
with sodium:
CH3 > 1° > 2° > 3°
36. Oxidation
H
R C OH
H
H
R C OH
H
Cr3O/pyridine = Collins reagent
H
R C OH
H
H
R-C=O
H
R-C=O
O
R-C-OH
Pyridinium chlorochromate (PCC)
CH2Cl2, 25oC
1o alcohol aldehyde
Cu or Cr3O/pyridine
1o alcohol aldehyde
KMnO4/H+ or K2Cr2O7/H+
or CrO3/H+
1o alcohol carboxylic acid
1° alcohol
37. O
PCC
Examples:
1° alcohol
CH3(CH2)4-CH2-OH CH3(CH2)4-C-H
KMnO4/H+ or K2Cr2O7/H+
CH3(CH2)4-CH2-OH CH3(CH2)4-C-OH
or CrO3/H+
O
1-hexanol hexanal
1-hexanol hexanoic acid
38. H
R C OH
R'
O
R-C-R'
KMnO4/H+ or K2Cr2O7/H+
or CrO3/H+
2o alcohol ketone
R"
R C OH
R'
KMnO4/H+ or K2Cr2O7/H+
3o alcohol
or CrO3/H+ no reaction
2° alcohol
3° alcohol
Example:
OH
CH3 CH
O
CH2CH3 CH3 C
CH2CH3
KMnO4/H+ or K2Cr2O7/H+
or CrO3/H+
2-butanol 2-butanone
39. Esterification
Esterification:
- the reaction between an alcohol and a carboxylic acid to
form an ester and H2O.
O
R C
O H H O R'
H+
O
CH3CH2-O-H CH3 C
O H
O
CH3-O-H C
OH
H+
R C
H+
O
O R'
O
CH3 C
O
C
OCH2CH3
OCH3
H2O
H2O
H2O
carboxylic acid alcohol ester
EXAMPLES
ethanol ethanoic acid ethyl ethanoate
methanol benzoic acid methyl benzoate
H+ = catalyst
40. Esterification also occurs when alcohols
react with derivatives of carboxylic acids
such as acid chlorides
O
CH3-O-H CH3 C
O
Cl CH3 C
OCH3
HCl
methanol ethanoyl chloride methyl ethanoate
41. Halogenation and haloform reactions
1) Hydrogen halides (HBr or HCl or HI)
R-OH + H-X → R-X + H2O
Example:
C2H5-OH + H-Br C2H5-Br + H2O
• Reactivity of hydrogen halides decreases in order HI >
HBr > HCl
• Reactivity of alcohols with hydrogen halides:
3° > 2° > 1°
H+
44. Dehydration
Dehydration of alcohols will formed alkenes and the
products will followed Saytzeff rules.
conc. H2SO4 R-CH2-CH2-OH R-CH=CH2 + H2O
Saytzeff rule:
- A reaction that produces an alkene would favour the
formation of an alkene that has the greatest number of
substituents attached to the C=C group.
CH3CH2-CH-CH3
OH
H+
H+
CH3CH2-CH=CH2 + H2O
1-butene
CH3CH=CH-CH3 + H2O
2-butanol
2-butene
major product
45. Reactivity of alcohols towards dehydration:
3° > 2° > 1°
Reagents for dehydration:
i) Concentrated H2SO4
conc. H2SO4 CH3-CH2-OH CH2=CH2 + H2O
ii) With phosphoric (v) acid
OH
85% H3PO4, 165-170oC H2O
iii) Vapour phase dehydration of alcohols
CH3CH2OH CH2=CH2 + H2O
Al2O3
heat
46. Formation of ether (Williamson ether
synthesis)
Involves the SN2 attack of an alkoxide ion on an
unhindered primary alkyl halides.
The alkoxide is made by adding Na, K or NaH to the
alcohol.
R-O- + R’-X → R-O-R’ + X-alkoxide
(R’ must be primary)
The alkyl halides (or tosylate) must be primary, so that
a back-side attack is not hindered.
If the alkyl halides is not primary, elimination usually
occurs to form alkenes.
47. CH3CH2-OH Na
CH3CH2-OH
CH3I
OH
CH3CH2-OTs
CH3CH2-O
Na+
CH3CH2-O-CH3
CH3I
NaI
CH3CH2-O-CH3
OCH2CH3
NaI
EXAMPLES
or
1) Na
2)
1) Na
2)
cyclohexanol ethoxycyclohexane
48. Question:
Alcohol W is a secondary alcohol with a molecular formula
of C4H10O.
Compound M C4H10O
Alcohol W
Step 1
CrO3 /
pyrridine
Step 2
H+ / heat
Compound N
(major)
+
Compound O
(minor)
Reagent A
C4H10ONa
a) Draw and give the IUPAC name for alcohol W.
b) Draw the structural formula for the following
compounds:
i) Compound M
ii)Compound N
iii)Compound O
49. c) Give the correct name for the following:
i) Step 1
ii) Step 2
iii)Reagent A
50. Answers
a) Alcohol W
OH
name: butan-2-ol
b) i) compound M ii) compound N iii) Compound O
O
c) i) Step 1: Oxidation
ii) Step 2: Dehydration (of alcohol)
iii) Reagent A: Na Metal
52. REACTION WITH SODIUM
OH Na O- Na+ 1/2 H2(g)
sodium phenoxide
REACTION WITH AQUEOUS SODIUM HYDROXIDE
OH NaOH O- Na+
sodium phenoxide
H2O
ROH + NaOH no reaction
53. ESTERIFICATION
OH
OH
NaOH
H2O
O
C
OH
O
ONa CH3CCl
NaOH
O
OC
O
OCCH3
H2O
NaCl
sodium phenoxide
phenyl benzoate
EXAMPLES
H+
54. HALOGENATION
More reactive towards electrophilic substitution than benzene.
ortho-para director.
1) Halogenation of phenol:
If liquid bromine or bromine water is added to an aqueous solution of phenol
at room temperature, decolorisation occurs and a white precipitate of 2,4,6-
tribromophenol is formed (bromination).
No catalyst (halogen carrier) is needed.
This reaction is used to test the presence of phenol and determine the mass
of phenol in an aqueous solution.
OH
3X2 (aq)
OH
3Br2(aq)
OH
X X
X
OH
Br Br
Br
3HX
3HBr
room
temperature
EXAMPLE
room
temperature
2,4,6-tribromophenol (white precipitate)
55. Phenol reacts similarly with chlorine or chlorine water to form
white precipitate of 2,4,6-trichlorophenol.
This reaction is called chlorination of phenol.
OH
3Cl2
OH
Cl Cl
room 3HCl
Cl
temperature
2,4,6-trichlorophenol (white precipitate)
Monobromophenols are obtained if the bromine is dissolved in
a non-polar solvent such as CCl4.
OH
2 2HBr
2Br2 (CCl4)
OH
Br
OH
Br
56. NITRATION
Dilute nitric (v) acids reacts with phenol at room
temperature to give a mixture of 2- and 4-nitrophenols.
OH
2 2HNO3
< 20oC 2H2O
OH
NO2
OH
NO2
2-nitrophenol 4-nitrophenol
57. By using concentrated nitric (v) acid, the nitration of
phenol yields 2,4,6-trinitrophenol (picric acid).
Picric acid is a bright yellow crystalline solid. It is used
in the dyeing industry and in manufacture of explosives.
OH
3HNO3
OH
NO2
NO2
O2N
3H2O
2,4,6-trinitrophenol
(picric acid)
58. CCHHEEMMIICCAALL TTEESSTTSS FFOORR PPHHEENNOOLLSS
Aqueous iron (III) chloride and aqueous bromine are used to
test phenols.
i) Complex formation with iron (III) chloride
- when two or three drops of iron (III) chloride solution is
added to a very dilute solution of phenol, a violet-blue
coloration is produced.
- methylphenol (toluene) produce a blue colour.
OH
O
6 FeCl3 (neutral) H3[Fe3+ ( )6]
3HCl
phenoxide ligand violet complex
59. Phenol
compound
Colour of
complex with
FeCl3 (aq)
Phenol
compound
Colour of
complex with
FeCl3 (aq)
Violet Green
Violet Red
Blue Violet
Violet
OH
OH
CH3
OH
CH3
OH
COOH
OH
R
O
OH
OH
OH
OCH3
O
60. ii) Bromine water
- when bromine water is added gradually to a concentrated
solution of phenol, the bromine water is decolorised.
- when excess bromine water is added, a white precipitate
of 2,4,6-tribromophenol is obtained.
61. TTEESSTTSS TTOO DDIISSTTIINNGGUUIISSHH CCLLAASSSSEESS OOFF
1) Lucas Test
AALLCCOOHHOOLLSS
- The alcohol is shaken with Lucas reagent (a solution
of ZnCl2 in concentrated HCl).
- Tertiary alcohol - Immediate cloudiness (due to the
formation of alkyl chloride).
- Secondary alcohol - Solution turns cloudy within
about 5 minutes.
- Primary alcohol - No cloudiness at room temperature.
62. CH3
CH3 C CH3
OH
CH3 CH
OH
CH2CH3
CH3CH2CH2CH2OH
CH3
CH3 C CH3
Cl
CH3 CH
Cl
CH2CH3
HCl/ZnCl2
room temperature
3o alcohol (cloudy solution almost immediately)
HCl/ZnCl2
room temperature
2o alcohol (cloudy solution within 5 minutes)
HCl/ZnCl2
room temperature
no reaction
1o alcohol
63. 2) Oxidation of alcohols
- only primary and secondary alcohols are oxidised by
hot acidified KMnO4 or hot acidified K2Cr2O7 solution.
- the alcohol is heated with KMnO4 or K2Cr2O7 in the
presence of dilute H2SO4.
- 1o or 2o alcohol:
→ the purple colour of KMnO4 solution disappears.
→ the colour of the K2Cr2O7 solution changes from
orange to green.
- 3o alcohol do not react with KMnO4 or K2Cr2O7.
65. HHAALLOOFFOORRMM TTEESSTT TTOO IIDDEENNTTIIFFYY MMEETTHHYYLL
AALLCCOOHHOOLL GGRROOUUPP
1) Iodoform:
Ethanol and secondary alcohols containing the group
methyl alcohol group which react with alkaline
solutions of iodine to form triiodomethane (iodoform,
CHI3).
Triiodomethane – a pale yellow solid with a
characteristic smell.
H
CH3 C
OH
(methyl alcohol group)
66. H
CH3 C R
OH
+ 4I2 + 6NaOH CHI3 (s) + RCOONa + 5NaI + 5H2O
triiodomethane
(iodoform)
yellow precipitate
where R = hydrogen, alkyl or aryl group
• The iodoform test can distinguish ethanol from methanol
H
CH3 C H
OH
+ 4I2 + 6OH CHI3 (s) + 5I- + 5H2O
iodoform
O
H C O
ethanol
methanoate
H
H C H
OH
+ 4I2 + 6OH
methanol
no reaction
positive iodoform test
negative iodoform test
67. • The iodoform test can distinguish 2-propanol from 1-propanol
CH3
CH3 C H
OH
+ 4I2 + 6OH CHI3 (s) + 5I- + 5H2O
iodoform
O
CH3 C O
2-propanol
ethanoate
positive iodoform test
H
H H
H C C C H
no reaction
OH
+ 4I2 + 6OH
H H negative iodoform test
1-propanol
* TERTIARY ALCOHOLS DO NOT GIVE POSITIVE
IODOFORM TEST
68. 2) BROMOFORM
H
CH3 C R
OH
+ 4Br2 + 6NaOH CHBr3 (s) + RCOONa + 5NaBr + 5H2O
bromoform
where R = hydrogen, alkyl or aryl group
sample
iodoform
reagent
69. Question:
a) Classify each of the following alcohols as
primary, secondary or tertiary.
i) 2-Propanol
ii) 4-methylpentanol
iii)2,3-dimethylbutan-2-ol
b) Name a simple test to distinguish 1°, 2°, 3°
alcohol. State the reagents and conditions
required for the test and write down the
expected observations.
70. Answer:
a) i) 2°
ii) 1°
iii) 3°
b) Test: Lucas test
Reagent and conditions : Lucas reagent /
Mixture of HCl and ZnCl2
Observatios:
- Clear homogenous solution change into 2
layers or cloudiness
- Rate of reaction: 3° > 2° > 1° alcohol
71. UUSSEESS OOFF AALLCCOOHHOOLLSS
As solvents:
- examples: the lower alcohols such as methanol,
ethanol and propanol.
- methanol is used as a solvent for varnish and paints.
As fuels:
- biofuel (fuel derived from a biological source).
- ethanol can be produced from sugars such as sucrose
from sugar cane, through fermentation and distillation.
It can be blended with petrol and used as fuel in motor
vehicles.
- methylated spirit is ethanol made undrinkable by the
addition of a little methanol. It is used as a fuel in
camping stoves.
72. In alcoholic drinks:
- ethanol is used for making wine, beer and etc.
As intermediates:
- methanol can be oxidised to methanal (HCHO), a
chemical feedstock (starting material) for the
manufacture of thermosetting plastics such as bakelite.
- methanol is used to make methyl methacrylate which
is used in the manufacture of another plastic called
perspex.
In cosmetics:
- ethanol is used as solvent for fragrances in perfumes
and after-shave lotions.
- polyhydroxyl alcohols (for example, glycerol) are used
in moisturising creams.
73. UUSSEESS OOFF PPHHEENNOOLLSS
Making plastics such as bakelite (phenol-methanal
plastic).
The synthesis of cyclohexanol and
hexanedioic acid to make nylon 6,6.
Making dyes.
Making antiseptics such as 4-chloro-3,5-
dimethylphenol which is active ingredient in
‘Dettol’.
