Transcript Level 3: Organics Part I

Level 3:
Organic Reactions Part I
Aldehydes
Ketones
Haloalkanes
Amines
Author: J R Reid
Aldehydes - Introduction
Aldehydes are very similar to
carboxylic acids in structure (but
they are missing the –OH)
Their names have ‘–al’ as a suffix
e.g. methanal, ethanal…
The smaller aldehydes are liquids
(except for methanal – a gas)
because of their polar bonds
The smaller molecules (below
hexanal) are soluble in water
Methanal is a gas that is dissolved
in water to create a disinfectant,
and to preserve biological
specimens in jars
H
H
C
H
O
C
H
Aldehydes - Production
As we saw in the extension of level 2 organics
section, aldehydes are made if you partially oxidise
a primary alcohol:
H3 C
CH2
OH
H3 C
CH
O
H3C
C
OH
O
This means that aldehydes can be oxidised further
to create carboxylic acids
Remember:
A thing that can be oxidised is called a reducing agent
(because it reduces someone else)
A thing that can be reduced is called an oxidising agent
(because it can reduce someone else)
Common oxidising agents (or oxidants) used to
create aldehydes are:
Acidified dichromate (Cr2O72-/H+)
Acidified permanganate (MnO4-/H+)
Ketones - Introduction
Ketones are very similar to
aldehydes except the double bond
is not at the end of a carbon chain
Their names have ‘–one’ as a suffix
e.g. propanone, butanone…
The smaller ketones are the same
as aldehydes. They are liquids
because of their polar bonding
The smaller molecules (below
hexanone) are soluble in water
Ketones are good solvents and are
often used for things like nail
polish remover (propanone) or
plastic model glue (butanone)
H
H
H
H
C
C
C
H
H
O
Ketones - Production
Ketones can be made by oxidising secondary
alcohols:
H3C
CH
CH3
H 3C
OH
C
CH3
O
Note: Tertiary alcohols cannot be oxidised at all.
The –OH can’t form double bonds with the carbon
that it is attached to because that carbon is already
bonded to three other carbons
CH3
H3C
C
OH
CH3
X
Aldehydes and Ketones –
The Tests
Aldehydes can be oxidised a little further
while ketones can not. This is the basis for
the various tests for difference between
these two chemicals:
Acidified permanganate/dichromate –
aldehydes will be oxidised and change the
colour of these two chemicals. BUT the colour
will also change if we have any primary or
secondary alcohols present because they can be
oxidised also
Benedict’s solution: This blue solution (Cu2+)
turns red/orange (Cu2O) when boiled with
aldehydes (but not with alcohols)
Tollen’s (silver mirror) test: This colourless
(Ag(NH3)2+) solution turns the test tube silver
(Ag) when aldehydes are present
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Haloalkanes
Can be classified as primary,
secondary and tertiary just like
alcohols.
Haloalkanes
Volatile, polar molecules but only
slightly soluble in water as no
hydrogen bonding can occur (except
fluorocarbons)
Melting points higher than alkanes
Examples: teflon – non stick frying
pans, chloroform – CHCl3 – used as a
solvent and in movies as an
anaesthetic, CCl4 – solvent used in drycleaning fluid until it was found to
cause liver damage
Haloalkane preparation
Prepared by :
substitution of an alcohol by thionyl
chloride
Addition of HX to an alkene
Substitution of an alkane in UV light
with a halogen eg: Br2
Haloalkane reactions
Nucleophilic substitution: A
nucleophile is any species that loves
nuclei – or is attracted to a positive
charge. Nucleophiles are species
carrying a lone pair of electrons or a
negative charge: eg: H2O, OH- or NH3
The C-X bond is polar is haloalkanes
and has a slightly positive charge. The
positive carbon is vulnerable to attack
by a nucleophile
3 types of nucleophilic
substitution reactions
1.
2.
3.
OH-(aq) forms an alcohol with a primary or
secondary haloalkane
H2O (l) forms an alcohol with a tertiary haloalkane
NH3(alc) forms an amine with a haloalkane. Note
(alc) means dissolved in alcohol. Why not water?
Chloroalkane elimination
reactions
Haloalkanes can form alkenes by
reacting with KOH(alc) or NaOH (alc).
Why alcoholic again solvent again?
Reverse of Markovnikovs rule applies.
Questions:
Write a balanced equation for the
reaction of bromoethane with aqueous
potassium hydroxide
Write a balanced equation for the
reaction between 2-iodobutane and
alcoholic ammonia
Write an equation for the reaction
between 2-methyl butan-2-ol and
alcoholic potassium hydroxide.
Properties of Esters
Have pleasant fruity smells and occur
naturally in plants. Used in
manufacture of everyday items such
as flavouring agents, perfumes.
Have the general formula R-COOR’.
Polar molecules but no hydrogen
bonding
Colourless volatile liquids
Insoluble in water
Naming: Part that comes from the
alcohol is an alkyl group, part from
the acid is –anoate on the end.
Eg: Ethanol and propanoic acid make
ethyl propanoate
Name the ester made
from:
1.
2.
3.
4.
5.
Propanoic acid and butanol
Ethanoic acid and methanol
Butanol and methanoic acid
Decanol and hexanoic acid
This one
Preparation of an ester
Condensation reaction of a carboxylic
acid with an alcohol, using
concentrated sulfuric acid as a catalyst
and dehydrating agent.
Reaction carried out by reflux.
Chemical Reactions
Hydrolysis (split with water) with
dilute acid to form the original acid
and alcohol
Hydrolysis with a basic solution eg:
NaOH to form the salt of the acid and
the alcohol. Used in soap manufacture.
React with ammonia or amines to
form an amide (slow reaction)
Making soap
Soaps are the sodium salts of fatty
acids (long chain acids). These salts
are soluble in water as they are
ionised, but they have a carbon chain
end that is soluble in fats and oils.
This allows them to dissolve and
break down dirt.
Sodium laurate is the name of the
soap molecule made from coconut oil
made by boiling it with sodium
hydroxide.
See page 97 for an
example
Amines - Introduction
Amines are organic compounds that contain nitrogen in their
structure (but no oxygen)
There are three types of amines: primary, secondary and
tertiary. Unfortunately we use these words slightly differently
than we do with alcohols and haloalkanes
Identify the trend…
Secondary
Primary
H3C
CH
NH2
CH3
H3C
CH2 NH
Tertiary
CH3
CH3
H3 C
N
CH3
Amines are bases (like ammonia) and smell like fish.
Most amines are liquids but aminomethane and aminoethane
boil below 20ºC
Amines – Naming and Source
The name of the primary amine
comes from the length of the
alkyl (alkane) chain attached to
the –NH2. For example, an amine
with a propane chain attached is
called aminopropane
(CH3CH2CH2NH2)
Primary amines are made using
the nucleophilic substitution of
haloalkanes (as we saw earlier)
H 3C
CH2
NH2
Amines - Reactions
Neutralisation
Because amines are bases they will neutralise acids to
create salts (just like ammonia)
CH3CH2NH2 + HCl
CH3CH2NH3Cl
Ionisation
Amines dissolve in water to create ions (just like
ammonia)
CH3CH2NH2 + H2O
CH3CH2NH3+ + OH-
Complex ion formation
Amines will form complex ions with Cu2+ (just like
ammonia)
4CH3CH2NH2 + Cu2+ Cu(CH3CH2NH3)2+
Nucleophilic Substitution
Of halolakanes….the primary amine
can act as a nucleophile and displace
the halogen atom in a haloalkane.
A secondary amine is formed