Transcript No Slide Title

Alcohols
Foundation in Science
Mahsa University College
Chem 2
Topic: Alcohol
Prepared by Mr. Daniel Philip
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Alcohols
An alcohol consists of a carbon chain with a hydroxy
group (-OH) attached
Methanol
Ethanol
Propanol
Phenol
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1. Naming and Drawing molecules
Nomenclature of Alcohols
a) Alcohols are named by dropping the e
ending of the parent alkane and replacing
with ol. The –OH group can also be
named as a substituent using the group
name, hydroxy.
b) Still another nomenclature involves
naming the alkyl group followed by a
space and the word alcohol
General formula of alcohols
CnH2n+2O
First member is Methanol
a) Displayed formula is
H
|
H-C-O-H
|
H
b) Systematic name: methanol
(from : methan + ol)
c) Structural formula - CH3OH
d) Molecular formula CH4O
Names and Structural formula of common alcohols
Examples:
CH3OH
CH3CH2OH
Methanol
Ethanol
CH3CH2CH2OH is called
propan-1-ol or 1-propanol
CH3CH(OH)CH3 is called
propan-2-ol or 2-propanol
if more than one hydroxyl is present, the
prefixes di-, tri-, tetra-... are used the
terminal "e" is retained on the parent
alkane name.
CH2OHCH(OH)CH2OH
Common name is Glycerol and
systematic name is 1,2,3-propanetriol.
Exercise 1
Give the displayed formula, structural
formula, molecular formula and
empirical formula of the following
alcohols
a)
b)
c)
d)
1-butanol
2-butanol
2-methyl-1-propanol
2-methyl-2-propanol
Name the following molecules:
Alcohol Classification
Alcohols may be classified as
- Primary
- Secondary
- Tertiary
Depending on whether the carbon atom
that is attached to the –OH group is
surrounded by one, two or three other
carbon atoms
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Primary Alcohols
A primary alcohol is bonded to carbon atom that is
bonded also to one or no carbon atom carbon atom.
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Secondary Alcohols
A secondary alcohol is attached to a carbon atom that
is bonded also to 2 carbon atoms.
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Tertiary Alcohols
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Polyhydroxy alcohols
Alcohols that have more than one OH group
are known as polyhydroxyl alcohols. Two
examples are shown below
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Name and classify the
following alcohols.
• 2-butanol
(Secondary)
• 2-propene-1-ol
(Primary)
• 2-methyl-1-butanol
(Primary)
• 2-methyl-2-butanol
(Tertiary)
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Properties of Alcohols
The physical properties of alcohols are similar
to those of both water and hydrocarbons
The shorter chain alcohols such as methanol and
ethanol are similar to water, in general they
-- have higher boiling points than hydrocarbons
but lower than water
-- dissolve in water to some degree
-- are more polar than hydrocarbons but less
polar than water
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Alcohols are polar
molecules
Reactivity:
• The image shows the electrostatic potential for methanol.
The more red an area is, the higher the electron density and the more
blue an area is, the lower the electron density.
• The alcohol O atom are a region of high electron density (red) due to
the lone pairs.
3. Physical properties
• 1. Boiling point is higher than
hydrocarbon. (Due to intermolecular H-bond)
• 2. Spirituous odour with burning taste.
• 3. Short chain alcohols, up till 4 carbon
atoms are soluble in water.
Extra info: Phenol (at room temperature) is
colourless liquid but tinged with pink
oxidation product. It is moderately soluble
in water. It is corrosive.
Exercise
1. Explain why ethanol liquid is soluble in
water but ethane gas isn’t soluble in
water.
4marks
2. Explain why the boiling point of
ethanol is greater than the boiling
point of ethane.
4marks
Reactions of Alcohols
Alcohols undergo several types of
reactions including:
Oxidation
Dehydration
Reactions with active metals
Esterification
Substitution
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4. Chemical reactions of Alcohols
4.1 Alcohol with alkali metals → alkoxide (strong base!)
2 Na + 2 CH3OH → H2(g) + 2 CH3O- + 2 Na+
(sodium methoxide)
4.2. Alcohol substitution
CH3CH2CH2OH + HCl → CH3CH2CH2Cl + H2O
CH3CH2OH + PCl5  CH3CH2Cl + HCl + POCl3
4.3. Alcohol dehydration
CH3-CH2-OH → CH2=CH2 + H2O
Chemical reactions of Alcohols
4.4 Alcohol oxidation (burning)
* primary alcohols → aldehydes
* secondary alcohols → ketones
* tertiary alcohols → no reaction
4.5 Alcohol with caboxylic acid for
Esterification reaction
alcohol + acid → ester + H20
4.4 Oxidation
Alcohols are oxidized to alkanals (aldehydes) or
alkanones (ketones) and even carboxylic acids.
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Primary Alcohols are Oxidized to Alkanals/Aldehyde
The most common oxidizing agents are acidic KMnO4
soultion or , acidic K2Cr2O7 or even oxygen from the
air(very very slow). The mechanisms of such reactions
are usually complex
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Secondary Alcohols are oxidized to Alkanones/Ketones
Example
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Tertiary Alcohols are not
easily oxidized
There is no hydrogen attached to the tertiary
carbon. It is not possible for a carbonyl group on
the tertiary carbon to be oxidixed.
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Tertiary Alcohols are not
easily oxidized
Furthermore the large R groups on the tertiary
carbon, prevent reacting groups. Hence tertiary
alcohols are rather unreactive.
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4.4. Oxidation
H
O
O
excess [O]
R
C
O H + [O]
R
C
H
R
OH
+ H2O
H
C
Aldehyde / Alkanal
Carboxylic acid
Primary alcohol
O
H
R
C
O H + [O]
R'
Secondary alcohol
R
C
Ketone
R'
Common O.A. :
K2Cr2O7/ H+,
KMnO4/ H+
Oxidizing agents are acidified KMnO4
or acidified K2Cr2O7
Primary alcohol with acidic oxidizing
agent solution, distilled, gives aldehyde
Primary alcohol with acidic oxidizing
agent solution, reflux boiling, gives
carboxylic acid
Secondary alcohol with acidic oxidizing
agent solution, reflux boiling, gives
ketone
Observation:
a)
acidified KMnO4 solution/acidified manganate(VII)
solution :
Purple to Colourless or purple is decolourised
Or
b) acidified K2CrO7 solution/acidified dichromate(VI)
solution :
Orange to Green
Exercise
Draw the displayed structure of the organic product
formed, if any when the following alcohol was
heated with acidified KMnO4 solution, reflux
(boiling)
a)
b)
c)
d)
e)
f)
g)
h)
Methanol
Ethanol
1-propanol
2-propanol
1-butanol
2-butanol
2-methyl-1-propanol
2-methyl-2-propanol
Draw the displayed structure of the organic
product formed, if any when the following
alcohol was mixed with acidified KMnO4
solution and the product is distilled off
a)
b)
c)
d)
e)
Methanol
Ethanol
1-propanol
1-butanol
2-methyl-1-propanol
4.3 Dehydration
Many alcohols undergo intramolecular dehydration,
removing water to form alkenes.
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4.3 Dehydration
Definition: removal of water from a molecule.
Extra info: H and OH are removed from two
adjacent carbons.
Reagent and conditions:Dehydrating agents
Con H2SO4, heat
Con H3PO4, heat
Solid SiO2, heat
Solid Al2O3, heat
Solid ceramic or solid pumice, heat
Exercise
Write an equation and then give the displayed structure
of the organic product formed, if any when the
following alcohol was heated with con.H2SO4 and
heated(warm/boil or reflux boiling)
a)
b)
c)
d)
e)
f)
g)
Ethanol
1-propanol
2-propanol
1-butanol
2-butanol
2-methyl-1-propanol
2-methyl-2-propanol
4.1 Reactions with Metals
• Alcohols are far less acidic than water but they
react with highly reactive metals such as potassium
and sodium.
• The metal replaces the hydrogen atom in the
alcohol group forming a salt and hydrogen gas
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Note that the reaction between Na,
sodium solid and alcohol at room
temperature releases colourless gas of
H2. This indicates the presence of OH
hydroxy group in alcohols.
Quick exercise
Write an equation for reaction between
Sodium metal at r.t. with
a) Methanol
b) Ethanol
c) 1-propanol
d) 2-propanol
Esterification
An alcohol reacts with an alkanoic acid to form
an ester and water.
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Write an equation and then give the displayed structure
of the organic product formed, if any when the
following alcohol was heated with ethanoic acid
with drops of con.H2SO4 and heated(warm/boil or
reflux boiling)
a)
b)
c)
d)
e)
f)
g)
h)
Methanol
Ethanol
1-propanol
2-propanol
1-butanol
2-butanol
2-methyl-1-propanol
2-methyl-2-propanol
Exercise
Ethanol undergoes the following reactions:
Reaction 1: Ethanol Ethene
Reaction 2: Ethanol  Ethanal
Reaction 3: Ethanol  Ethanoic acid
Reaction 4: Ethanol  CH3CH2ONa
Reaction 5: Ethanol  CH3CH2CO2CH2CH3
Reaction 6 : Ethanol to CH3CH2Cl
a)
Name the type of organic reaction in reaction labelled as:
1:…………………………………
2 :…………………………………
3 :…………………………………
4 :…………………………………
5 :…………………………………
6:…………………………………
Ethanol undergoes the following reactions:
Reaction 1: Ethanol Ethene
Reaction 2: Ethanol  Ethanal
Reaction 3: Ethanol  Ethanoic acid
Reaction 4: Ethanol  CH3CH2ONa
Reaction 5: Ethanol  CH3CH2CO2CH2CH3
Reaction 6 : Ethanol to CH3CH2Cl
b) Give the reagents and conditions for reaction labelled as
1:…………………………………
2 :…………………………………
3 :…………………………………
4 :…………………………………
5 :…………………………………
6:………………………………….
Ethanol undergoes the following reactions:
Reaction 1: Ethanol Ethene
Reaction 2: Ethanol  Ethanal
Reaction 3: Ethanol  Ethanoic acid
Reaction 4: Ethanol  CH3CH2ONa
Reaction 5: Ethanol  CH3CH2CO2CH2CH3
Reaction 6 : Ethanol to CH3CH2Cl
C) Give the observation for reaction labelled as
1:…………………………………
2 :…………………………………
3 :…………………………………
4 :…………………………………
5 :…………………………………
6: ……………………………………..
Ethanol undergoes the following reactions:
Reaction 1: Ethanol Ethene
Reaction 2: Ethanol  Ethanal
Reaction 3: Ethanol  Ethanoic acid
Reaction 4: Ethanol  CH3CH2ONa
Reaction 5: Ethanol  CH3CH2CO2CH2CH3
Reaction 6 : Ethanol to CH3CH2Cl
d) Name the organic products of reaction labelled as
4:………………………..
5:………………………..
6:………………………..
Ethanol undergoes the following reactions:
Reaction 1: Ethanol Ethene
Reaction 2: Ethanol  Ethanal
Reaction 3: Ethanol  Ethanoic acid
Reaction 4: Ethanol  CH3CH2ONa
Reaction 5: Ethanol  CH3CH2CO2CH2CH3
Reaction 6 : Ethanol to CH3CH2Cl
e) Give the displayed formula of organic prodct formed from
reaction labelled as
1:
2:
3: