2.2.1 Alcohols
Topic
Naming of alcohols and
Less
on
1
(a) Explain in terms of hydrogen bonding, the water
solubility and the relatively low volatility of alcohols.
Objectives - Students should be able to:
Naming alcohols.
classify alcohols as primary, secondary or
tertiary
explain their water solubility and relatively
low volatility
(d) classify alcohols into primary, secondary and tertiary
alcohols.
(b) Describe the industrial production of ethanol by:
(i) fermentation of sugars i.e. from glucose
(ii) the reaction of ethene with steam in the presence of an
acid catalyst (H3PO4)
(c) Outline for alcohols :
(i) the use of ethanol in alcoholic drinks and as a solvent in
the form of methylated spirits
(ii) the use of methanol as a petrol additive to improve
combustion and its increasing importance as a feedstock in
the production of organic chemicals
2
describe and explain the industrial production
of ethanol by fermentation from sugars or the
reaction of steam with ethene
Compare the disadvantages and advantages of
each method in terms of:
Sustainability, sepapartion costs, energy costs
recall important uses of alcohols
PRACTICAL
3
(f) Describe the oxidation of alcohols using dichromate/sulphuric
acid including:
Demo the two oxidations of of ethanol
(ILPAC 8.1 B,C)
(i) the oxidation of primary alcohols to aldehydes and carboxylic
acids; the control of the oxidation product using different reaction
conditions.
(ii) the oxidation of secondary alcohols to form ketones
(iii) the resistance to oxidation of tertiary alcohols.
(f) Describe the oxidation of alcohols using dichromate/sulphuric
acid including:
4/5
(i) the oxidation of primary alcohols to aldehydes and carboxylic
acids; the control of the oxidation product using different reaction
conditions.
describe the action of K2Cr2O7/H2SO4 on
primary, secondary and tertiary alcohols
understand how the product from the oxidation
of primary alcohols can be controlled using
different reaction conditions
(ii) the oxidation of secondary alcohols to form ketones
(iii) the resistance to oxidation of tertiary alcohols.
(h) Describe the elimination of water from alcohols in the
presence of an acid catalyst and heat to form alkenes.
6
Class practical.
Dehydration of alcohol as in ILPAC 8.1
Collect the ethene and test it with bromine and
acidified potassium permanganate.
Then construct all of the possible isomers
including E/Z that could be obtained by
dehydrating a variety of alcohols.
(g) Describe the process of esterification of alcohols with
carboxylic acids in the presence of an acid catalyst.
TEST
7
Carry out various esterifications by combining
the acid and alcohol in the presence of conc
sulphuric acid and pouring onto solid sodium
carbonate and practice writing equations or
esterification. Naming esters is also difficult
and will require practice.
8
Test learning of Alcohols
2.2.2 Halogenoalkanes
Syllabus
(a) Describe the hydrolysis of halogenalkanes as a
substitution reaction.
(d) Explain the relative rates of hydrolysis of primary
halogenalkanes in terms of the relative bond enthalpies of
the carbon-halogen bonds. Aqueous silver nitrate may be
used to compare the rates but in this reaction water is
assumed to be the nucleophile.
Alternatively hot aqueous alkali can be used (followed by
neutralisation and addition of aqueos silver nitrate). In
this reaction OH- is the nucleophile.
Lesson
1
Objectives - Students should be able to:
Hydrolysis of Halogenalkanes
Name a few halogenalkanes and classify as
primary, secondary and tertiary.
Carry out an experiment to compare how the
rate of hydrolysis of primary halogenoalkanes
varies with respect to carbon-halogen bonds
[C-Cl, C-Br, C-I] (ILPAC 5.3) Does the rate
of reaction depend upon bond polarity or
bond strength?
Give equations for reactions of
halogenalkanes with H2O, KOH and NaOH.
(b) Define the term nucleophile as an electron pair donor.
(c) Describe the mechanism of nucleophilic substitution
in the hydrolysis of halogenoalkanes with hot
aqueous alkali.
2
Nucleophilic substitution
define the term nucleophile
understand why halogenoalkanes are
susceptible to attack by nucleophiles
write out the nucleophilic substitution
mechanism for hydrolysis of primary
halogenoalkanes [i.e. SN2] (typical example:
bromoethane) and describe the conditions
Then write a similar mechanism for the
reaction with other nucleophiles such as
ammonia and CN- (although reactions are not
in syllabus)
(a) Outline the uses of chloroethene and tetrachloroethen to
produce the plastics PVC and PTFE.
3
Uses of CFC’s and damage to the ozone
layer
How Science works. Initial use of CFC’s as harmless aerosol
propellants offset when scientists discovered that CFC’s
damaged the ozone layer.
Cover the syllabus points opposite but always
relate to chemical properties.
(f) Explain that CFC’s:
Why do they have a low volatility?
(i) were developed as aerosols, refrigerants, and in air
conditioning because of their low reactivity, volatility and
no-toxicity.
Why are they not toxic?
(ii) but caused environmental damage to the ozone layer –
this provided important evidence which enabled
international action to be taken to reduce and phase out CFC
use.
(iii) Subsequently green chemistry has minimised damage to
the environment by promoting biodegradable alternatives to
CFC’s such as hydrocarbons and HCFC; and have used CO2
instead as a blowing agent for expanded polymers. The
ozone layer has naturally repaired itself.
Talk about the strong C-F and C-Cl bonds in
CFC’s which resist hydrolysis – hence their
durability in the atmosphere and non
biodegrability.
Then link to AG/AK work:
2O3 = 3O2 is catalysed by Cl free radicals
released by the action of uv light on CFCs.
Look at alternatives..
Good article in ILPAC book.
2.2.3 Modern Analytical Techniques
Syllabus points
(a) state that the absorption of IR radiation causes covalent
bonds to vibrate
(b) identify using an infrared spectrum of an organic
compound:
(i) an alcohol from an O-H bond absorbing
(ii) an aldehyde or ketone from a C=O bond absorbing
(iii) a carboxylic acid from a C=O bond and the borad
absorption of the O-H bond.
(Use Data sheet and be aware that most organic
compounds also give a sharp peak at approximately
3000cm-1 due to the absorption of C-H bonds.
(c) State that modern breathalysers measure ethanol in the
breath by analysis using infra red spectroscopy.
(d) outline the use of mass spectrometry:
(i)
in the determination of relative isotopic masses
(ii)
as a method for identifying elements i.e. use in the
Mars space probe and monitoring levels of
environmental pollutants such as lead/pestcides in the
food chain.
(e) interpret mass spectra of elements in terms of isotopic
abundances
Lesson Outline
1
Show molecular models to show a covalent bond
vibrating.
Talk about natural frequency of vibration akin to a
spring.
Resonance i.e. greater amplitude of vibration with
infra red that corresponds to the natural frequency
of vibration of the bond.
Stronger bonds absorb at higher frequencies (E=hv)
Then give the pupils a variety of alcohols,
aldehydes, ketones, carboxylic acid infra red
spectra and ask them to identify the functional
groups present from the spectrum.
Then talk about how a breathalyser can determine
the concentration of alcohol in your breath from the
degree of absorbance of radiation by the O-H peak.
2
Although it says knowledge of the structure of the
mass spectrometer in not required think that
running through its structure will aid the students
understanding.
Calculate RAM from mass spectra
Look at data from the Mars space probe.
3
Define a molecular ion.
Discuss that the electron gun can cause a molecule
(f) use the molecular ion peak in a mass spectrum of an
organic molecule to determine its molecular mass.
(g) Suggest the identity of the major fragment ions i.e. m/z =
29 as CH3CH2+ in a given mass spectrum (limited to
alkenes, alkanes and alcohols)
(h) Use molecular ion peaks and fragmentation peaks to
identify structures (limited to unipositive ions)
(i) Explain that a mass spectrum is essentially a fingerprint
for a molecule that can be identified by a computer using a
spectral database.
to fragment.
Look at some examples of alcohols and alkanes and
alkenes and how they would fragment.
Suggest what major fragments would the different
mass spectra of all of the structural isotopes of
butanol result in. The uniqueness of a mass spectra
can then be used from a database to identify a
molecule.
Then give the pupils some mass spectra from which
to identify various alkanes, alkenes and alcohols.
Identify the molecular mass first and then the major
fragments. Use the fragments to identify which
isomer is present.