chapter 1 alcohol
TRANSCRIPT
CHAPTER 1:
ALCOHOLS
NORFAZRIN MOHD HANIF FACULTY OF APPLIED SCIENCE
UITM NEGERI SEMBILAN
Nomenclature – common and IUPAC names for alcohols & phenols
Classification of alcohol as 1°, 2°, and 3°.
Physical properties of alcohol. Preparation of alcohol
–Grignard synthesis –Hydrolysis of alkyl halides –Industrial and laboratory preparations of ethyl alcohol
Reactions of alcohol –Oxidation –Esterification –Dehydration –Halogenation –Formation of alkoxides
SUBTOPICS
Alcohols are compounds whose molecules have a hydroxyl group
(-OH) attached to:
saturated C atom of a simple alkyl group
unsaturated C atom of an alkenyl or alkynyl group
Compounds that have –OH group attached directly to a benzene ring
are called phenol
CH3 OH CH2 OHCH3 CH2 CH3CH3
OH
Methanol Ethanol 2-Propanol
CH CH2 OHCH2
2-Propenol
CH CH2 OHCH
2-Propynol
OHPhenol
INTRODUCTION
• According to the type of carbinol carbon atom (C bonded to the –OH group).
C OHClasses:
i) Primary alcohol
- -OH group attached to a primary carbon atom
- one or no alkyl group attached to the carbon bonded to the –OH group
ii) Secondary alcohol
- -OH group attached to a secondary carbon atom
- two alkyl group attached to the carbon bonded to the –OH group
iii) Tertiary alcohol
- -OH group attached to a tertiary carbon atom
- three alkyl group attached to the carbon bonded to the –OH group
CLASSIFICATION
Primary (1°) Alcohol Secondary (2°) Alcohol
H C C
H
H OH
H
C H
H
H
Tertiary (3°) Alcohol
H C C
H
H OH
C
C H
H
H
HH
H
H C C
H
H H
H
C OH
H
H
CLASSIFICATION
• 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.
Polyhydroxy Alcohols
CLASSIFICATION
Select the longest
continuous chain of carbon
atoms containing –-OH .
Change the name of the
alkane corresponding to this
chain by dropping the final-e
and adding the suffix –ol.
Number the parent chain to
give the -OH group the lowest
possible number.
1 2
3 a. IUPAC names
b. Common names
Name the alkyl group followed by the word alcohol
NOMENCLATURE
1-Propanol(Propyl alcohol)
2-Propanol(Isopropyl alcohol)
1-Butanol(Butyl alcohol)
OH
OH
OH
2-Butanol(sec-Butyl alcohol)
2-Methyl-1-propanol(Isobutyl alcohol)
2-Methyl-2-propanol(tert -Butyl alcohol)
OH
OHOH
Examples
IUPAC :
COMMON:
IUPAC :
COMMON:
NOMENCLATURE
Compounds containing more than one -OH group are named diols, triols, etc.
C H 3 C H C H 2
H O O H
C H 2 C H 2
O H O H
C H 2 C H C H 2
H O H O O H
1,2-Ethanediol (Ethylene glycol)
1,2-Propanediol (Propylene glycol)
1,2,3-Propanetriol (Glycerol, Glycerine)
NOMENCLATURE
Unsaturated alcohols
Name compounds containing a double bond and an alcohol group as alkenol.
Give the alcohol carbon the lower number.
Examples:
3-Buten-2-ol
C CH CH CH3
OH
CH3
CH3
4-Methyl-3-penten-2-ol
CH2 CH CH CH3
OH
NOMENCLATURE
Unsaturated alcohols
Name compounds containing a triple bond and an alcohol group as alkynol. Give the alcohol carbon the lower number. Examples:
CH C CH2CH2 OH
3-Butyn-1-ol
C CHCH2C
OH
CH3
CH3
2-Methyl-4-Pentyn-2-ol
NOMENCLATURE
Phenols is the parent name & the substituent is simply indicated by prefix.
COMMON:
IUPAC: phenol 3-Bromophenol 2-Methylphenol
NOMENCLATURE - Phenol
COMMON:
IUPAC: 1,2-Benzenediol 1,3-Benzenediol 1,4-Benzenediol
NOMENCLATURE - Phenol
• 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.
PHYSICAL PROPERTIES
Alcohols are polar compounds
they interact with themselves and with other polar
compounds by dipole-dipole interactions
Dipole-dipole interaction: the attraction between the positive end of one dipole and the negative end of another
O
HH
H
CH
+
-
+
O
HH
H
CH
+
-
+
…………….........
hydrogen
bonding
PHYSICAL PROPERTIES
Hydrogen bonding: when the positive end of one dipole is a H bonded to F, O, or N (atoms of high electronegativity) and the other end is F, O, or N
▫ the strength of hydrogen bonding in water is approximately 21 kJ (5 kcal)/mol
▫ hydrogen bonds are considerably weaker than covalent bonds
▫ nonetheless, they can have a significant effect on physical properties
PHYSICAL PROPERTIES
In relation to alkanes of comparable size and molecular weight, alcohols
– have higher boiling points
– are more soluble in water
The presence of additional -OH groups in a molecule
further increases solubility in water and boiling point
Boiling point & solubility
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.
A. Solubility
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.
A. Solubility
Use basic solubility rule: “like dissolves like”
Each alcohol consists of a nonpolar carbon chain
(hydrophobic part) and a polar OH group (hydrophilic part).
As water is polar, it attracts OH group while carbon chain
on the other hand as nonpolar is repelled. Solubility of
alcohols is determined by the stronger of the two forces.
Another factor in understanding solubility is the capability
to form hydrogen bonding to water.
H O
H δ+
O
HH
H
CH
+
-
+
…………..
hydrogen
bonding
A. Solubility
Structural Formula Name bp(°C)
Solubilityin Water
Methanol 32 65 Infinite
Ethane 30 -89 Insoluble
Ethanol 46 78 Infinite
Propane 44 -42 Insoluble
1-Propanol 60 97 Infinite
Butane 58 0 Insoluble
1-Pentanol 88 138 2.3 g/100 g
1,4-Butanediol 90 230 Infinite
Hexane 86 69 Insoluble
8 g/100 g117741-Butanol
Pentane 72 36 Insoluble
CH3 CH2 CH2 OH
CH3 CH2 CH2 CH3
CH3 OH
CH3 CH3
CH3 CH2 OH
CH3 CH2 CH3
CH3 ( CH2 ) 3 CH2 OH
HOCH2 ( CH2 ) 2 CH2 OH
CH3 ( CH2 ) 4 CH3
CH3 ( CH2 ) 2 CH2 OH
CH3 ( CH2 ) 3 CH3
MW
A. Solubility
i) 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.
RO
HO
H R
ArO
HO
H Ar
hydrogen bonding hydrogen bonding
δ+
δ-
δ+ δ-
δ-
δ-
ii) Branched chain alcohols boils at a lower temperature (more volatile) than the straight chain alcohols with the same number of carbon atoms.
B. Boiling point
• Their boiling points are dramatically different
– ethanol forms intermolecular hydrogen bonds which increase attractive forces between its molecules resulting in a higher boiling point
– there is no comparable attractive force between molecules of dimethyl ether & ethane.
bp -24°C Ethanol bp 78° C
Dimethyl ether
C H 3 C H 2 O H C H 3 O C H 3 C H 3 C H 3 Ethane
bp -89°C
B. Boiling point
OCTOBER 2008
APRIL 2009
• 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 R-O- + H3O+ K
a Ka = [H3O
+] [RO-]
[ROH]
pKa = - log (Ka)
* More smaller the pKa
value, the alcohol is
more acidic
C. Acidity
Alcohol is weakly acidic.
In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O-).
CH3 O H : HO
H
[ CH3OH]
[ CH3O-] [H3O
+]
CH3 O:–
O
H
HH+
+
= 10- 15 .5
pKa = 1 5.5
Ka =
+
pKa decrease, acidity increase
alkoxide ion
C. Acidity
(CH3 ) 3COH
(CH3 ) 2CHOH
CH3CH2OH
H2 O
CH3OH
CH3COOH
HCl
15.5
15.7
15.9
17
18
4.8
Hydrogen chloride
Acetic acid
Methanol
Water
Ethanol
2-Propanol
2-Methyl-2-propanol
Structural Formula
Stronger acid
Weaker acid
*Also given for comparison are pKa values for water, acetic acid, and hydrogen chloride.
Compound pKa
-7
C. Acidity
Acidity depends primarily on the degree of stabilization and solvation of the alkoxide ion
▫ the negatively charged oxygens of methanol and ethanol are about as accessible as hydroxide ion for solvation; these alcohol are about as acidic as water
▫ as the bulk of the alkyl group increases, the ability of water to solvate the alkoxide decreases, the acidity of the alcohol decreases, and the basicity of the alkoxide ion increases
CH3OH
Methanol
H2O
Water
pKa = 15.5 pKa = 15.7
CH3CH2OH
Ethanol
pKa = 15.9
CH3CH2(OH)CH3
2-Propanol
pKa = 17.0
C. Acidity
• Phenol is a stronger acid than alcohols and water.
OH H2O O- H3O
+
phenol phenoxide ion
R-OH + H2O R-O- + H3O+ Ka = ~ 10-16 to 10-18
alcohol alkoxide ion
Ka = 1.2 x 10-10
H2O + H2O HO- + H3O+ Ka = 1.8 x 10-16
hydroxide ion
C. Acidity of phenols
Phenol is more acidic than alcohols by considering the resonance effect.
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
C. Acidity of phenols
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.
C. Acidity
Grignard Synthesis Hydrolysis of alkyl halides Acid-catalyzed Hydration of
alkenes
PREPARATION
• The grignard reagent (RMgX) is prepared by the reaction of
metallic magnesium with the appropriate organic halide. This
reaction is always carried out in an ether solvent, which is
needed to solvate and stabilize the Grignard reagent as it forms.
R-X + Mg R-Mg-X
(X = Cl, Br or I) organomagnesium halide
(Grignard reagent)
CH3CH2OCH2CH3
Grignard reagents may be made from primary, secondary, and
tertiary alkyl halides, as well as from vinyl and aryl halides.
Alkyl iodides are the most reactive halides, followed by bromides
and chlorides. Alkyl fluorides generally do not react.
1.Grignard Synthesis
CH3I Mg
CH3CH2Br Mg
Br Mg
CH3MgI
MgBr
CH3CH2MgBr
EXAMPLES
ether
ether
ether
1.Grignard Synthesis
Grignard Reagents react with Formaldehyde to give a 1° alcohol
General formula:
R MgX + C O
CH3
CH3
Ether
H3O+
R C OH
CH3
CH3
Grignard reagent
alcohol
Carbonyl compound
CH3CH2 MgBr + C O
H
H
Ether
H3O+
CH3CH2 C OH
H
H
alkyl halide
alcohol
1.Grignard Synthesis
• Grignard reagents
act as nucleophiles
toward the carbonyl
group
R MgX + C O
R'
R''
Ketone
R C O
R'
R''
MgXNH
4Cl
R C OH
R'
R''
3o alcohol
H2O
Grignard Reagents react with ketone to give a 3° alcohol
Ether
Grignard Reagents react with all other aldehyde to give a 2° alcohol
R MgX + C O
R'
H
aldehyde
R C O
R'
H
MgXH
3O+
R C OH
R'
H
2o alcohol
Ether
1.Grignard Synthesis
General formula:
Alkyl Halide Alcohol
Examples:
R X + OH- R OH + HXΔ
CH3 Cl + OH- CH3 OH + HClΔ
CH3CH2CH2 Cl + OH- ?Δ
(CH3)2CH Br + OH- ?Δ
2. Hydrolysis of alkyl halide
• Alkyl halides can be
converted to
alcohols using
water or hydroxide
as the nucleophile.
• Mechanism is a
simple nucleophilic
substitution
General formula:
C C
CH3
CH3
CH3
CH3
Alkene
+ H2O
H+
C C
H
CH3
CH3
CH3
OH
CH3
Examples:
H2C CH2
Ethene
+ H2O
H+
C C
H
H
H
H
OH
H
Ethanol
Industrial &
laboratory
preparation of
ethanol
3. Acid catalyzed hydration of alkene
• Note that this is not
a reaction
mechanism, but an
equation for the
overall reaction.
• Hydronium ion is a
required catalyst.
Examples:
C CHCH3
CH3
CH3
2-Methyl-2-butene
+ H2O
H+
C C
CH3
OH
CH3
H
H
CH3
2-Methyl-2-butanol
+ C C
CH3
H
CH3
OH
H
CH3
3-Methyl-2-butanol
* Markovnikov’s rule : in the addition of H-OH to an alkene, the H atom adds to
the C atom of the double bond that already has the greater number of H atom.
(Major product) (Little formed)
3. Acid catalyzed hydration of alkene
Oxidation Dehydration Halogenation Esterification Formation of alkoxides
REACTION
1. Oxidation
Oxidation of 1°Alcohol to Aldehyde : RCH2-OH RCHO
CH3CH2OH + PCCCH
2CI
2CH3 C H
O
Ethanol Ethanal25oC
PCC: Pyridinium chlorochromate
Oxidation of 1°Alcohol to Carboxylic Acid : RCH2-OH RCOOH
CH3CH2OH CH3 C OH
O
Ethanol Ethanoic Acid
H2CrO
4
acetone35oC
CH3CH2OH CH3 C OH
O
Ethanol Ethanoic Acid
KMnO4/ H+
[O]
[O]
1. Oxidation
Oxidation of 2°Alcohol to Ketone : RCHR'
OH[O]
R C R'
O
CH3CHCH2
OH
CH3
H2CrO
4
2-Butanol
acetone35oC
CH3CCH2
O
CH3
2-Butanone
KMnO4/H+
cyclohexanol cyclohexanone
OH O
1. Oxidation
A Chemical Test for 1o, 2o and 3o Alcohol
CH3CH2OH CH3 C OH
O
Ethanol Ethanoic Acid
H2CrO
4
acetone35oC
+ Cr3+
orange
green 1oAlcohol
2oAlcohol
3oAlcohol H
2CrO
4
2-Methyl-2-propanol
acetone35oC
CH3 C CH3
OH
CH3
No reaction!
H2CrO
4
2-Butanol 2-Butanoneacetone
35oC
CH3CHCH2CH3
OH
CH3C CH2CH3
O
orange
green
+ Cr3+
1. Oxidation
• When heated with strong acids catalysts (most commonly H2SO4,
H3PO4), alcohols typically undergo a reactions to generate an alkene and
water. Also known as dehydration since it involves the removal of a
molecule of water.
• Dehydration of alcohols will formed alkenes and the products will followed
Zaitsev’s rule .
conc. H2SO4
R-CH2-CH2-OH R-CH=CH2 + H2O
CH3CH2-CH-CH3
OH
H+
H+
CH3CH=CH-CH3 + H2O
CH3CH2-CH=CH2 + H2O
2-butanol2-butenemajor product
1-butene
2. Dehydration
* Zaitsev’s rule : The major product of the reaction favor the more stable alkene.
Dehydration of Alcohol to form Alkene:
+ H2O
H+
C C
CH3
CH3 CH3
CH3
C C
CH3
CH3
CH3OH
CH3
CH3180oC
+ H2O
H+
C C
CH3
CH3
CH3OH
CH3
CH3C C
CH3
CH3
CH3 OH
CH3
O C C
CH3
CH3
CH3
CH3
CH3
140oC
Dehydration of Alcohol to form Ether:
2. Dehydration
Examples:
CH3CH2OH
CH2 CH2
CH3CH2OCH2CH3
Ethene
Diethyl ether
H+
H+
180oC
140oC
2. Dehydration
Halogenation of Alcohol to form Alkyl halide from
1. Hydrogen Halide (H-X)
2. Phosphorus trihalide (PX3)
3. Thionyl Chloride (SOCl2)
R OH + H X R X + H2O
alkyl halidehydrogen halide
X = Cl, Br, I
CH3CH2OH + H Br CH3CH2 Br + H2O
Examples:
1. Hydrogen Halide (H-X)
3. Halogenation
LUCAS’S TEST:
(CH3)3COH + H Cl (CH3)3C Cl + H2O
ZnCl2
25oC3o
(CH3)2CHOH + H Cl (CH3)2CH Cl + H2O
ZnCl2
25oC2o
CH3CH2CH2CH2OH + H Cl No reactionZnCl
2
25oC1o
•LUCAS TEST : used to differentiate 3o, 2o and 1o alcohol.
• Alcohol’s reactivity : 3o>2o>1o
Immediate white
cloudiness of solution
formed
White cloudiness of
solution formed after 5
min
Clear homogenous solution
Clear homogenous solution
Clear homogenous solution
3. Halogenation
2. Phosphorus trihalide (PX3)
CH3 OH + P Br3 CH3 Br
3. Thionyl Chloride (SOCl2)
CH3 OH + SOCl2 CH3 Cl + SO2 + HCl
3R OH + P X33R X + H
3PO
3
X = Cl, Br, I
R OH + SOCl2 R Cl + SO2 + HCl
3. Halogenation
The reaction between an alcohol and a carboxylic acid to form
an ester and H2O.
R C
O
O H O R'H
H+
CH3CH2-O-H CH3 C
O
O H
CH3-O-H C
O
OHH
+
H+
R C
O
O R'
C
O
OCH3
CH3 C
O
OCH2CH3
H2O
H2O
H2O
carboxylic acid alcohol ester
EXAMPLES
ethanol ethanoic acid ethyl ethanoate
methanol benzoic acid methyl benzoate
H+ = catalyst
4. Esterification
General formula:
R C Cl
O
R' OH + R C OR'
O
+ HCl
Acid Chloride Ester
Esterification also occurs when alcohols react with
derivatives of carboxylic acids such as acid chlorides
C6H5C Cl
O
CH3OH + C6H5C OCH3
O
+ HCl
Examples:
4. Esterification
2R OH + 2RO Na + H22Na
- +
2R OH + 2RO K + H22K
- +
General formula:
R OH + NaOH no reaction
alkoxide salt
alkoxide salt
* Reactivity towards active metal: 1o>2o>3o alcohol
5. Formation of alkoxides
End of Chapter 1…
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