Hydroxyl Compounds

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ORGANIC CHEMISTRY
CHM 207
CHAPTER 6:
HYDROXYL COMPOUNDS
(ALCOHOLS AND PHENOL)
NOR AKMALAZURA JANI
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)
•
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.
ALCOHOLS
• Alcohols: Organic compounds containing hydroxyl (-OH)
functional groups.
R

OH
Phenols: Compounds with hydroxyl group bonded directly
to an aromatic (benzene) ring.
OH
NOMENCLATURE OF
ALCOHOLS
IUPAC RULES
1.
2.
3.
4.
Select the longest continuous chain of carbon atoms
containing the hydroxyl group.
Number the carbon atoms in this chain so that the one
bonded to the –OH group has the lowest possible number.
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.
Name each alkyl branch chain (or other group) and designate
its position by number.
This is the longest continuous chain that contains
an hydroxyl group.
Select this chain as the parent compound.
4
3
2
1
This end of the chain is closest to the OH.
Begin numbering here.
4
3
2
1
3-methyl-2-butanol
This is the longest continuous chain that contains
an hydroxyl group.
Select this chain as the parent compound.
5
4
3
2
1
This end of the chain is closest to the OH.
Begin numbering here.
5
4
3
2
3-methyl-2-pentanol
1
NOMENCLATURE OF CYCLIC
ALCOHOLS
• Using the prefix cyclo• The hydroxyl group is assumed to be on C1.
H
OH
6 1
5
43 2
Br
IUPAC name:
HO CH2CH3
1
H
trans-2-bromocyclohexanol
new IUPAC name: trans-2-bromocyclohexan-1-ol
3
2
1-ethylcyclopropanol
1-ethylcyclopropan-1-ol
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.
EXAMPLE
5
4
CH2 CH
3
CH2
2
1
CH CH3
OH
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
• 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
CH3
3
CH
O
2
CH2
1
C
OH
3-hydroxybutanoic acid
4 3 2
5 1
6
OH
O
2-hydroxycyclohexanone
MAIN GROUPS
decreasing priority
Acids
Esters
Aldehydes
Ketones
Alcohols
Amines
Alkenes
Alkynes
Alkanes
Ethers
Halides
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.
5
OH
3
CH3
IUPAC name
2
CH
1
CH2
propane-1,2-diol
1
4
OH
OH
3 2
OH
trans-cyclopentane-1,2-diol
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
O2N
OH
CH3CH2
Br
IUPAC name:
2-bromophenol
common name: ortho-bromophenol
OH
3-nitrophenol
meta-nitrophenol
4-ethylphenol
para-ethylphenol
• Phenols may be monohydric, dihydric or trihydric
according to the number of hydroxyl groups present
in the benzene ring.
OH
OH
OH
OH
OH
benzene-1,3-diol
OH
benzene-1,4-diol
OH
benzene-1,2,3-triol
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
TYPE
i)
ii)
Primary (1°)
Secondary (2°)
STRUCTURE
H
R C
H
EXAMPLES
CH3
OH
R'
R C OH
H
CH3CH2-OH
CH3CHCH2 OH
ethanol
2-methyl-1-propanol
OH
H3C CH CH2CH3
2-butanol
iii)
Tertiary (3°)
R'
R C OH
R''
OH
cyclohexanol
CH3
H3C C OH
CH3
2-methyl-2-propanol
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.
PHYSICAL PROPERTIES
• 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.
• BOILING POINTS
- The boiling points of alcohols are higher than those of alkanes and
chloroalkanes of similar relative molecular mass.
- For example:
C2H5OH
Relative molecular mass:
Boiling point:
46
CH3CH2CH3
44
78°C
CH3Cl
50.5
-42°C
-24°C
- Reason:
intermolecular hydrogen bonds exist between the –OH
groups in the alcohol molecules.
Ar δδ+
R δδ+
Ar
O
H
R
O
H
OδOδH hydrogen bonding
H
hydrogen bonding
- Branched chain alcohols boils at a lower temperature (more
volatile) than the straight chain alcohols with the same number of
carbon atoms.
• 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 nonpolar end (the alkyl group) called ‘hydrophobic’.
- the water solubility decreases as the alkyl group becomes larger.
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.
* Phenol is unusually soluble (9.3%) because of its compact shape and
the particularly strong hydrogen bonds formed between phenolic –
OH groups and water molecules.
ACIDITY OF ALCOHOLS AND PHENOLS
• Alcohol is weakly acidic.
• In aqueous solution, alcohol will donated its proton to water
molecule to give an alkoxide ion (R-O-).
R-O- + H3O+
R-OH + H2O
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
Ka = [H3O+] [RO-]
[ROH]
R-O- + H3O+
pKa = - log (Ka)
* More smaller the pKa
value, the alcohol is
more acidic
Acidity OF PHENOLS
• Phenol is a stronger acid than alcohols and water.
R-OH + H2O
alcohol
OH
R-O- + H3O+
Ka = ~ 10-16 to 10-18
alkoxide ion
H2O
phenol
H 2 O + H2 O
O-
+
H3O
Ka = 1.2 x 10-10
phenoxide ion
HO- + H3O+
hydroxide ion
Ka = 1.8 x 10-16
• 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.
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
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.
REACTIONS OF ALCOHOLS
•
•
•
•
•
•
Reaction with sodium
Oxidation
Esterification
Halogenation and haloform reactions
Dehydration
Formation of ether (Williamson ether
synthesis)
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°
Oxidation
H
1° alcohol
R
C OH
Pyridinium chlorochromate (PCC)
H
CH2Cl2, 25oC
R-C=O
H
1o alcohol
aldehyde
H
R
C OH
Cu or Cr3O/pyridine
H
R-C=O
H
o
1 alcohol
Cr3O/pyridine = Collins reagent
aldehyde
H
R
C OH
H
1o alcohol
KMnO4/H+ or K2Cr2O7/H+
or CrO3/H+
O
R-C-OH
carboxylic acid
Examples:
1° alcohol
O
CH3(CH2)4-CH2-OH
PCC
1-hexanol
CH3(CH2)4-CH2-OH
1-hexanol
CH3(CH2)4-C-H
hexanal
KMnO4/H+ or K2Cr2O7/H+
or CrO3/H+
O
CH3(CH2)4-C-OH
hexanoic acid
H
+
2° alcohol
R
C OH
+
KMnO4/H or K2Cr2O7/H
O
+
or CrO3/H
R'
R-C-R'
ketone
2o alcohol
R"
3° alcohol
R
C OH
KMnO4/H+ or K2Cr2O7/H+
no reaction
+
or CrO3/H
R'
3o alcohol
Example:
OH
CH3 CH CH2CH3
2-butanol
+
+
KMnO4/H or K2Cr2O7/H
or CrO3/H+
O
CH3 C
CH2CH3
2-butanone
Esterification
• Esterification:
- the reaction between an alcohol and a carboxylic acid to form an
ester and H2O.
O
R
C
O
H
H O
carboxylic acid
CH3CH2-O-H
ethanol
R'
O
CH3
C
methanol
O
R'
H2O
O
H+
O
H
ethanoic acid
C OH
benzoic acid
C
ester
O
CH3-O-H
R
alcohol
EXAMPLES
H+ = catalyst
O
H+
CH3
C
OCH2CH3
ethyl ethanoate
H+
O
C OCH3
methyl benzoate
H2O
H2O
Esterification also occurs when alcohols
react with derivatives of carboxylic acids
such as acid chlorides
O
O
CH3-O-H
CH3 C Cl
CH3 C OCH3
methanol
ethanoyl chloride
methyl ethanoate
HCl
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
H+
Reactivity of hydrogen halides decreases in order HI > HBr > HCl
Reactivity of alcohols with hydrogen halides:
3° > 2° > 1°
2) Phosphorus trihalides, PX3
3R-OH + PX3
3R-X + H3PO3
(PX3 = PCl3 or PBr3 or PI3)
Example:
(CH3)2CHCH2-OH + PBr3 → (CH3)2CHCH2-Br
isobutyl alcohol
isobutyl bromide
3) Thionyl chloride (SOCl2)
R-OH + SOCl2 → R-Cl + SO2 + HCl
Example:
CH3(CH2)5CH2-OH + SOCl2 → CH3(CH2)5CH2-Cl + SO2 + HCl
1-heptanol
1-chloroheptane
Dehydration
• Dehydration of alcohols will formed alkenes and the products
will followed Saytzeff rules.
R-CH2-CH2-OH

conc. H2SO4
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.
+
H
CH3CH2-CH-CH3
OH
2-butanol
H+
CH3CH2-CH=CH2 + H2O
1-butene
CH3CH=CH-CH3 + H2O
2-butene
major product
• Reactivity of alcohols towards dehydration:
3° > 2° > 1°
• Reagents for dehydration:
i) Concentrated H2SO4
CH3-CH2-OH
conc. H2SO4
CH2=CH2 + H2O
ii) With phosphoric (v) acid
OH
85% H3PO4, 165-170oC
iii) Vapour phase dehydration of alcohols
CH3CH2OH
Al2O3
heat
CH2=CH2 + H2O
H2O
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’ + Xalkoxide
(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.
EXAMPLES
CH3CH2-OH
+
Na
CH3CH2-O Na
CH3CH2-O-CH3
CH3I
NaI
or
CH3CH2-OH
OH
1) Na
2) CH3I
1) Na
CH3CH2-O-CH3
OCH2CH3
2) CH3CH2-OTs
cyclohexanol
ethoxycyclohexane
NaI
REACTIONS OF PHENOLS
•
•
•
•
Reaction with sodium
Esterification
Halogenation of the ring
Nitration of the ring
REACTION WITH SODIUM
OH
Na
O- Na+
1/2 H2(g)
sodium phenoxide
REACTION WITH AQUEOUS SODIUM HYDROXIDE
OH
NaOH
O- Na+
sodium phenoxide
ROH + NaOH
no reaction
H2O
ESTERIFICATION
EXAMPLES
O
OH
NaOH
ONa
H2O
O
CH3CCl
NaCl
OCCH3
NaOH
sodium phenoxide
O
OH
C OH
O
H+
OC
phenyl benzoate
H2O
HALOGENATION
• More reactive towards electrophilic substitution than benzene.
• ortho-para director.
OH
OH
X
3X2
X
room
temperature
3HX
X
EXAMPLES
OH
OH
Br
3Br2
Br
room
temperature
3HBr
Br
2,4,6-tribromophenol (white precipitate)
OH
OH
Cl
3Cl2
Cl
room
temperature
3HCl
Cl
2,4,6-trichlorophenol (white precipitate)
• Monobromophenols are obtained if the bromine
is dissolved in a non-polar solvent such as CCl4.
OH
2
OH
OH
Br
2Br2 (CCl4)
2HBr
Br
NITRATION
• Dilute nitric (v) acids reacts with phenol at room temperature to
give a mixture of 2- and 4-nitrophenols.
OH
2
OH
OH
2HNO3
< 20oC
NO2
2H2O
NO2
2-nitrophenol
4-nitrophenol

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
OH
3HNO3
O2N
NO2
NO2
2,4,6-trinitrophenol
(picric acid)
3H2O
TESTS TO DISTINGUISH CLASSES OF
ALCOHOLS
1)
Lucas Test
- 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.
CH3
CH3
HCl/ZnCl2
CH3 C CH3
OH
room temperature
Cl
o
3 alcohol
CH3 CH CH2CH3
OH
(cloudy solution almost immediately)
HCl/ZnCl2
room temperature
(cloudy solution within 5 minutes)
HCl/ZnCl2
room temperature
o
1 alcohol
CH3 CH CH2CH3
Cl
2o alcohol
CH3CH2CH2CH2OH
CH3 C CH3
no reaction
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.
+ Cr2O2-7 + 8H+
3RCH2OH
1o alcohol
(orange)
(orange)
3RCOOH
(green)
R'
3 R CH OH + Cr2O2-7 + 8H+
o
+ 2Cr3+ + 7H2O
carboxylic acid
R'
2 alcohol
(green)
aldehyde
3RCHO + Cr2O2-7 + 8H+
aldehyde
+ 2Cr3+ + 7H2O
3RCHO
(orange)
3R C
ketone
3+
O + 2Cr + 7H2O
(green)
HALOFORM TEST TO IDENTIFY METHYL
ALCOHOL GROUP
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)
H
CH3
C
R + 4I2 + 6NaOH
OH
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
O
H + 4I2 + 6OH
-
CHI3 (s) + 5I + 5H2O
iodoform
OH
H
C
O
methanoate
ethanol
positive iodoform test
H
H
C
H + 4I2 + 6OH
OH
methanol
no reaction
negative iodoform test
• The iodoform test can distinguish 2-propanol from 1-propanol
CH3
CH3
C
O
CHI3 (s) + 5I- + 5H2O
H + 4I2 + 6OH
2-propanol
H
H
H
H
C
C
C
H
H
OH
1-propanol
C
O
ethanoate
iodoform
OH
CH3
positive iodoform test
H + 4I2 + 6OH
no reaction
negative iodoform test
* TERTIARY ALCOHOLS DO NOT GIVE POSITIVE
IODOFORM TEST
2) BROMOFORM
H
CH3
C
R + 4Br2 + 6NaOH
CHBr3 (s) + RCOONa + 5NaBr + 5H2O
bromoform
OH
where R = hydrogen, alkyl or aryl group
reagent
sample
iodoform
USES OF ALCOHOLS
• 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.
• 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 aftershave lotions.
- polyhydroxyl alcohols (for example, glycerol) are used in
moisturising creams.
USES OF PHENOLS
• 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-3,5dimethylphenol which is active ingredient in
‘Dettol’.
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