Transcript Functional Groups and Preparations

FUNCTIONAL GROUPS AND
PREPARATIONS
FUNCTIONAL GROUPS
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The functional group of alkanes is the C-C bond,
the alkenes C=C bond and so on
TETRAHEDRAL CARBON COMPOUNDS
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In addition to the alkanes the other tetrahedral
compounds are the Chloroalkanes and the
Alcohols
CHLOROALAKNES
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Historically surgery was extremely painful and
people only underwent surgery if it was
absolutely essential
One of the early anaesthetics was Chloroform
(CHCl3) (modern name tri-chloro methane)
Chloroform is an example of a chloroalkanes
Chloroalkanes are defined as compounds in
which one or more of the hydrogen atoms in
an alkane molecule have been replaced by a
Chlorine atom
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Chloroalkanes have the same basic tetrahedral
shape as the corresponding alkanes and like
alkanes they are all saturated compounds
NB fig 22.1 p 341 for some common structures
They are rarely found naturally and are usually
synthesised in a laboratory
PROPERTIES OF CHLOROALKANES
Most are liquid at room temperature
 Their main use is as solvents to remove oil
and grease marks from machinery and in the dry
cleaning of clothes
 Paint stripper contains dichloromethane (can
you draw this???)
 They are insoluble in water (due to having
very little polarity)
 They readily dissolve in non-polar solvents
such as cyclohexane
 They are suitable solvents for things such as
tippex but they cause damage to the ozone layer
so scientists are looking for alternatives
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NAMING CHLOROALKANES
Find the parent chain of carbons and get the
chain name (ie meth, eth, but)
 Determine the carbon the chlorine is attached to
 Determine the number of chlorines attached
 Eg. 2 –chlorobutane
 Eg. 2,2, 3 trichlorohexane
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ALCOHOLS
The alcohol in alcoholic drinks is ethanol and is
just one of many alcohols
 Methanol, ethanol, propanol, Butanol etc. All
exist and are named according to the number of
carbons in the parent chain
 One thing all alcohols have in common is their
functional group which gives them their
characteristic properties
 This is the Hydroxyl group (OH)
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REMEMBER
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Each carbon atom is basically tetrahedral shaped
but the carbon with the OH group attached is vshaped
12g
10cm3
10cm3
4cm3
PREPARATION OF ETHANAL
The first test tube should
be discarded.
 Add small amounts of
calcium carbide as it is
very reactive with water
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PREPARATION OF ETHANAL
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Why is it necessary to turn
off the Bunsen burner or
heating element before the
reaction is started?
The reaction would become
too vigorous, and some
unreacted ethanol and
other material is likely to be
forced over into the conical
flask. Once the mixture in
the reaction vessel has been
brought to the boil, further
heating is not required as
the oxidation of ethanol is
an exothermic reaction, and
gentle boiling can be
maintained by regulating
the flow from the dropping
funnel.
KETONES
Functional group of ketones is C-C=O
C
The only structural difference between aldehydes
and ketones is that hydrogen atom in ketones is
replaced by an alkyl group
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Rememeber AldHydes have the H the Hydrogen
Because the carbonyl group has two alkyl groups
attached it can never be at the end of the chain
There are only two ketones on your course
PROPERTIES OF KETONES
Higher boiling points than corresponding alkanes
(due to presence of dipole-dipole forces)
 Boiling points are lower than those of
corresponding alcohols due to lack of hydrogen
bonding
 The polarity of the carbonyl group in lower
members of the ketones causes them to be very
soluble in water
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PREPARATION OF ETHANOIC ACID
Reflux (20 mins)
5g of sodium dichromate
5cm3 of sulphuric acid
Cool flask with tap water
PREPARATION OF ETHANOIC ACID
1. Mix 2 cm3 of ethanol and 10 cm3
of deionised water in the dropping
funnel.
2.Add the solution from the dropping
funnel dropwise down the
condenser, while swirling the
contents of the flask and cooling it
if necessary to prevent too
vigorous a reaction.
Cool the apparatus,
dismantle and rearrange
for distillation
PREPARATION OF ETHANOIC ACID
Round flask used
instead of pear shaped
PRECAUTIONS
Reflux distillation involves condensing the
vapour from a boiling liquid in such a way as to
return the condensed material to the reaction
vessel.
 In this way a reaction may be carried out at quite
a high temperature while preventing the loss of
any of the reactants or products.
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ESTERS
ESTERS ARE PREPARED IN LAB BY THE
REACTION BETWEEN AN ALCOHOL AND A
CARBOXYLIC ACID
The lower members of the ester family are volatile
liquids with pleasant fruit smells.They give scent to
fruit
and flowers
Uses of organic acids
•Esters are used as artificial perfumes or scents as
they emit a sweet smell.
•Esters are used in making artificial food flavours that
are added in many edible items like ice creams, soft
drinks, sweets, etc.
•Esters are used as industrial solvents for making
cellulose, fats, paints and varnishes.
•Esters are used as solvents in pharmaceutical
industries.
•Esters are used as softeners in plastic industries
and molding industries
3 fatty acids and
glycerol
Practical set
up
Reflux
Distillation
SAPONIFICATION
SOAP
AROMATIC CMPOUNDS
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Aromatic compounds are compounds that contain
a benzene ring structure in their molecules
Benzene is planar
 Benzene is non polar as there is a small
electronegativity difference between hydrogen
and carbon
 It was traditionally used as a solvent but was
found to be carcinogenic so methyl benzene
(toluene is now used instead)
 Would you predict it would be soluble in water or
cyclohexane?
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ORGANIC NATURAL PRODUCTS
Many organic compounds are found in nature
and are referred to as “natural products”
 Examples include caffeine, benzaldehyde (in
almonds), nicotine, quinine and limonene
 19th century mainly concerned with finding ways
to isolate useful compounds such as morphine
 Now it is possible to work out the molecular
structures and synthesize these in the laboratory
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STEAM DISTILLATION
This is a method of extracting oils from plants
 It involves distillation in a current of steam
 It is very important to avoid too high a
temperature as the oil may become damaged
 If the oil and water separate naturally they can
be isolated using a tap funnel
 If an emulsion is obtained (where the oil drops
are dispersed throughout the water) then an
organic solvent that will dissolve the oil but not
the water needs to be used
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The organic solvent can be separated from the
water with a tap funnel
 The organic solvent may then be evaporated and
a pure sample of the oil remains
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