Amines and organic synthesis Flashcards
Introduction to Amines
which homologous series do amines belong to?
amines are a homologous series of organic molecules that contain a nitrogen atom
if we replace the hydrogen atoms in ammonia by alkyl or aryl groups, what do we get?
we get different amines
what is the simplest amine?
methylamine (CH3NH2)
what type of amine is it?
primary amine
what group do all primary amines have?
all primary amines contain the amino group (–NH2)
How can we name simple amines?
using the alkyl group prefix
when is a different prefix used, what is this prefix called?
is isomers exist the amino group is numbered and the prefix used is amino
draw out 2 structures, ethylamine, propylamine, which of the two structures uses the prefix amino?
propylamine changes to 1-aminopropane
Practice naming/ drawing the following amines:
1. 1-amino-2-methylpropane
2. phenylamine
3. phenylmethylamine
How are amines classified?
primary, secondary or tertiary
primary amines contain how many aryl or alkyl groups attached to the nitrogen atom?
Draw what this looks like?
1 aryl or alkyl group attached to the nitrogen atom
which amines are the most important?
primary amines
Why are the boiling points lower for the corresponding alcohol?
because hydrogen bonding is not as strong
How many aryl or alkyl groups do secondar amines have attached to the nitrogen atom?
Draw what this looks like
Contain 2 aryl or alkyl groups attached to the nitrogen atom
give 2 examples of a secondary amine, and draw each structure out?
- N-ethylaminoethane
- N-methylanimoethane
In tertiary amines, how many aryl or alkyl groups are attached to the nitrogen atom?
3
Give an example of a tertiary amine? Draw out the structure of this amine
N,N-dimethylaminomethane
what are the 3 properties of amines?
- can act as bases
- can act as nucleophiles
- can act as ligands
what do the properties of nitrogen depend on?
depned on the ability of nitrogen atom to donate a lone pair of it’s electrons to other species
explain what happens when a nitrogen atoms acts as a base?
when amines act as bases the lone pair is donated to a proton (H+)
explain what happens when a nitrogen atom acts as a nucleophile?
when amines act as nucleophiles the lone pair is donated to an electron deficient carbon atom
explain what happens when a nitrogen atom acts as a ligand?
when amines act as ligands the lone pair is donated to a transition metal ion
what type of bases does amines and ammonia act as?
Bronstead-Lowry bases
what are bronstead lowry bases?
proton acceptors
why does amines and ammonia act as a Bronstead lowry base?
they act as Bronstead-Lowry bases because the lone pair of electrons on the nitrogen atom allows them to accept a proton
Draw a diagram to show how they act as bases?
amines are also what type of bases?
Lewis bases - electron pair donors
Why do amines react with acid?
Because they are bases
what does amines and Acid make?
Soluble ionic salts
questions:
1.methylamine + HCL –>
2. ethylamine + HNO3 –>
3. phenylamine + HCL –>
4. ethylamine + H2SO4 –>
what does amines in water make?
an alkaline solution
why does amines in water make an alkaline solution?
Show this reaction between methylamine + water –>
because there are OH- ions present
e.g CH3NH2 + H20 –> CH3NH3+ + OH-
what does the base strength of amines depend on?
depends on the availability of the lone pair of electrons on the nitrogen atom for protonation
stronger bases have …?
increased availability of the lone pair
are primary aliphatic amines stronger bases or ammonia?
primary aliphatic molecules
why are primary aliphatic amines stronger bases than ammonia?
- Primary aliphatic molecules are stronger bases than ammonia due to the presence of the alkyl group
- alkyl groups are electron releasing and increase the availability of the lone pair
- the effect increases with alkyl chain length
what increases as the chain length increases?
increases the availability of the lone pair more
are tertiary amines or secondary amines stronger bases?
yes tertiary are stronger bases
are secondary amines or primary amines stronger bases?
secondary amines
describe why tertiary amines are stronger bases than secondary amines and why secondary amines are stronger than primary amines?
- tertiary amines are stronger bases than secondary amines which are stronger bases than primary amines.
- this is because with more alkyl groups attached to the nitrogen the availability of the lone pair is increased due to increased electron releasing
Are primary aromatic amines or ammonia stronger bases
Primary aromatic molecules are weaker bases than ammonia
explain why Primary aliphatic molecules are weaker bases than ammonia?
- Primary aliphatic molecules are weaker bases than ammonia
- this is because the lone pair on the nitrogen atom get’s involved in aromatic delocalisation.
- the lone pair is less available due to delocalisation
why is phenylmethylamine a similar strength to primary aliphatic molecules?
Phenylmethylamine (C9H5CH2NH2) the nitrogen atom is not directly attached to the ring so the lone pair does nt become delocalised and the base strenght is similar to aliphatic amines
what can we use to compare relative base strengths of amines?
Pka values
Stronger bases have …? pKa values
Higher
what is the pKa of propylamine methylamine ammonia and phenylamine, order them in decreasing strength?
propylamine (10.84) > methylamine (10.64) > Ammonia (9.25) > Phenylamine (4.62)
How can we calculate the pKa from Ka?
-log[Ka]
what equilibrium does pKa values refer to?
RNH3+ —-> RNH2 + H+
Preparing Primary amines
what is a good method for making primary aliphatic amines?
in a 2 step synthesis: n
1. reaction of a haloalkane with potassium cyanide (aq alcoholic conditions ) via Nucleophilic substitution (cyanide ion :CN- nucleophile) formation of a nitrile RC≡N (increase in carbon chain length)
2. reduction of the nitrile to a primary amine via catalytic hydrogenation (H2/Ni catalyst)
Draw out the reaction to form a primary amine from 1-iodopropane
butanenitrile formed which is then reduced to form butylamine
How are Primary aromatic amines formed?
usually made by the reduction of nitro compounds
-but can also be reduced from a Benzonitrile to Phenylmethylamine
What reagent is not powerful enough to reduce CN group?
NaBH4 but LiBH4 is!!!
How can nitro groups be reduced?
- catalytic hydrogenation (H2/ Ni catalyst)
- using metal acid combinations (e.g Sn/Fe and HCL )
Show the reduction of nitrobenzene and 3-nitro 1-phenylethanone
why is metal acid combos a better alternative to using Catalytic hydrogenation for 3-nitro 1-phenylethanone
- metal acid combos can be used to selectively reduce the nitro group in benzene
- in the above example we can not use catalytic hydrogenation because the ketone group would also be reduced to a 2° alcohol.
- And metal acid combinations are weaker reducing agents and will not reduce the ketone (only reduce the nitro group)
what are the uses of primary aromatic amines?
- very useful intermediate in organic synthesis
- used to make synthetic dyes (azo dyes)
what is the rubbish way of making primary amines?
reaction of a haloalkane with excess ammonia in a sealed container
(primary amines are formed as the major product)
why can ammonia undergo nucleophilic substitution?
- ammonia (:NH3) has a lone pair of electrons on it’s nitrogen atom and is a nucleophile
- the ammonia nucleophile attacks the electron deficient carbon atom (δ+) (polar-polar carbon-halogen bond) and substitution takes place
Draw out the full reaction mechanism to show how chloropropane reacts with ammonia to form a primary amine
when primary amines are made this way what can they act as?
primary amines have a lone pair of electrons on the nitrogen atom and can themselves act as nucleophiles and can go and react with another haloalkane
what does this primary amine form when reacted with another haloalkane?
a secondary amine is formed via nucleophilic substitution
the secondary amine product then goes..?
and attacks another haloalkane molecule via nucleophilic substitution to make a tertiary amine
the tertiary amine formed then goes..?
Attacks another haloalkane via nucleophillic substitution
What product is made?
a quaternary ammonium salt
why can this not behave as a nucleophile?
no lone pair on the nitrogen atom so cannot behave as a nucleophile
what is the shape of this Cation?
the cation has a tetrahedral shape
what are the uses of quaternary ammonium salts?
used as cationic surfactants in fabric conditioners and hair products
How do cationic surfactants reduce static?
cationic surfactants coat the surface of the clothes or hair (with positive charges) and reduce the static due to negatively charged electrons.
what do quaternary ammonium salts that are used for cationic surfactants usually have?
usually have 2 long alkyl chains and 2 short alkyl chains
controlling the products of the reaction of ammonia
Subheading
what is formed when Haloalkane reacts with ammonia?
a mixture of products is usually formed
How can the mixture be separated?
with difficulty
How is the possibility of further substitution reduced and a higher yield
if a large excess of ammonia is used
How is a high yield of quaternary ammonium obtained?
By using a large excess of haloalkane
Amines and ammonia as nucleophiles
amines and ammonia act as..?
Nucleophiles
what are nucleophiles?
nucleophiles have a lone pair of electrons that they can donate to form a covalent bond
Amines and ammonia undergo?
- nucleophilic substitution reactions with haloalkanes
- nucleophilic addition-elimination reaction with acyl chlorides and acid anhydrides
Amines and ammonia undergo what reaction with acyl chlorides and acid anhydrides?
Nucleophilic-addition-elimination reactions
Ammonia and amines undergo nucleophilic substitution reactions with haloalkanes
Title
when haloalkanes are warmed with an excess of ammonia in a sealed container, what is formed?
primary amines are formed as the major product
what is formed when 1-chloropropane reacts with Ammonia?
Draw the word equation
CH3CH2CH2CL + 2NH3 —> CH3CH2CH2NH2 + NH4CL
why can ammonia attack the haloalkane?
- ammonia has a lone pair of electrons on the nitrogen atom and is a nucleophile
- the ammonia nucleophile attacks the electron deficient δ+ carbon atom (polar carbon-halogen bond) and substitution takes place
draw the mechanism to show how 1-chloropropane reacts with ammonia
what primary amine is formed?
CH3CH2CH2NH2 (1- aminopropane)
why can primary amines act as nucleophiles themselves?
primary amines have a lone pair of electrons on the nitrogen atom
the primary alkane can go on to react with another 1-chloropropane to make..?
a secondary amine (CH3CH2CH2)2NH - N-propylaminopropane and (propylammonium chloride)
Draw the next part of the mechanism to show the further substitution reaction between 1-aminopropane and haloalkane
what makes the secondary amine product a good nucleophile?
has 2 electron releasing alkyl groups so can go and react with another 1-chloropropane molecule
what is formed?
a tertiary amine (CH3CH2CH2)3N - N,N-dipropylaminopropane and (CH3CH2CH2)2NH2CL (Dipropylammonium chloride)
this tertiary amine can go and react with more haloalkane to form..?
a quaternary ammonium salt (CH3CH2CH2)4N+ CL-
Why can the quaternary ammonium salt not be a nucleophile?
there is no lone pair on the nitrogen of the quaternary ammonium so it can not behave as a nucleophile
controlling the products of reaction of ammonia with a haloalkane
title
when is multiple substitution favoured?
if there is an excess of haloalkane
formation of a secondary amine is favoured if there is an excess of..?
Haloalkane
when is the formation of the tertiary amine favoured?
if there is an excess Haloalkane
Ammonia and amines undergo nucleophilic addition-elimination reactions with acyl chlorides and acid anhydrides
title
draw out the word equation to show how ethanoyl chloride reacts with ammonia?
ethanoyl chloride + ammonia –> ethanamide + ammonium chloride
CH3COCL + 2NH3 –> CH3CONH2 + NH4CL
draw the mechanism to show the above reaction
draw out the word equation to show the reaction between ethanoyl chloride and methylamine?
ethanoyl chloride + methylamine –> N-methylethanamide + methyl-ammonium chloride
CH3COCL + 2CH3NH2 —> CH3CONHCH3 + CH3NH3+CL-
Draw the mechanism to show the above reaction
what are primary aromatic amines used to make?
synthetic dyes (azo dyes)
what are the uses of quaternary ammonium salts?
are used as cationic surfactants in fabric conditioners and hair products
amines are used to make polymers such as..?
polyurethanes and polyamides
what are examples of polyurethanes?
cavity wall insulation, lycra etc
what are examples of polyamides?
nylon fibres for clothes, carpets, toothbrushes
what are other uses of amines?
used to make many drugs such as pethidine a painkiller
Organic synthesis
what is the role of organic chemists
organic chemists need to find efficient (and cost effective) ways of synthesising useful complex organic compounds from simple starting materials
why do we need to do organic synthesis?
we need to be able to work out and piece together synthetic routes to molecules using all reactions we have encountered in Y12 and Y13
How many steps can an organic synthesis question have?
several steps
why do chemists design specific synthetic routes?
chemists try to design synthetic routes that use non-hazardous starting material
why do chemists use non-hazardous starting materials?
to make processes safer and also to reduce any impact on the environment
what else do chemists try to use?
also try use steps that do not require a solvent
why is this?
such steps avoid waste and and the need to separate the solvent at the end of the reaction. Solvents can also be a risk to safety as they’re often flammable and toxic
what do chemists aim to design?
chemists aim to design production methods that have high atom economies and high percentage yields
why is this?
such processes convert more of the starting materials into useful products and are less wasteful
For the following questions, outline and draw out the mechanisms and state the reaction conditions needed
FINISHED
