Amines and organic synthesis Flashcards
(121 cards)
1
Q
Introduction to Amines
A
2
Q
which homologous series do amines belong to?
A
amines are a homologous series of organic molecules that contain a nitrogen atom
3
Q
if we replace the hydrogen atoms in ammonia by alkyl or aryl groups, what do we get?
A
we get different amines
4
Q
what is the simplest amine?
A
methylamine (CH3NH2)
5
Q
what type of amine is it?
A
primary amine
6
Q
what group do all primary amines have?
A
all primary amines contain the amino group (–NH2)
7
Q
How can we name simple amines?
A
using the alkyl group prefix
8
Q
when is a different prefix used, what is this prefix called?
A
is isomers exist the amino group is numbered and the prefix used is amino
9
Q
draw out 2 structures, ethylamine, propylamine, which of the two structures uses the prefix amino?
A
propylamine changes to 1-aminopropane
10
Q
Practice naming/ drawing the following amines:
1. 1-amino-2-methylpropane
2. phenylamine
3. phenylmethylamine
A
11
Q
How are amines classified?
A
primary, secondary or tertiary
12
Q
primary amines contain how many aryl or alkyl groups attached to the nitrogen atom?
Draw what this looks like?
A
1 aryl or alkyl group attached to the nitrogen atom
13
Q
which amines are the most important?
A
primary amines
14
Q
Why are the boiling points lower for the corresponding alcohol?
A
because hydrogen bonding is not as strong
15
Q
How many aryl or alkyl groups do secondar amines have attached to the nitrogen atom?
Draw what this looks like
A
Contain 2 aryl or alkyl groups attached to the nitrogen atom
16
Q
give 2 examples of a secondary amine, and draw each structure out?
A
- N-ethylaminoethane
- N-methylanimoethane
17
Q
In tertiary amines, how many aryl or alkyl groups are attached to the nitrogen atom?
A
3
18
Q
Give an example of a tertiary amine? Draw out the structure of this amine
A
N,N-dimethylaminomethane
19
Q
what are the 3 properties of amines?
A
- can act as bases
- can act as nucleophiles
- can act as ligands
20
Q
what do the properties of nitrogen depend on?
A
depned on the ability of nitrogen atom to donate a lone pair of it’s electrons to other species
21
Q
explain what happens when a nitrogen atoms acts as a base?
A
when amines act as bases the lone pair is donated to a proton (H+)
22
Q
explain what happens when a nitrogen atom acts as a nucleophile?
A
when amines act as nucleophiles the lone pair is donated to an electron deficient carbon atom
23
Q
explain what happens when a nitrogen atom acts as a ligand?
A
when amines act as ligands the lone pair is donated to a transition metal ion
24
Q
what type of bases does amines and ammonia act as?
A
Bronstead-Lowry bases
25
what are bronstead lowry bases?
proton acceptors
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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
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Draw a diagram to show how they act as bases?
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amines are also what type of bases?
Lewis bases - electron pair donors
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Why do amines react with acid?
Because they are bases
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what does amines and Acid make?
Soluble ionic salts
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questions:
1.methylamine + HCL -->
2. ethylamine + HNO3 -->
3. phenylamine + HCL -->
4. ethylamine + H2SO4 -->
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what does amines in water make?
an alkaline solution
33
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-
34
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
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stronger bases have ...?
increased availability of the lone pair
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are primary aliphatic amines stronger bases or ammonia?
primary aliphatic molecules
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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
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what increases as the chain length increases?
increases the availability of the lone pair more
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are tertiary amines or secondary amines stronger bases?
yes tertiary are stronger bases
40
are secondary amines or primary amines stronger bases?
secondary amines
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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
42
Are primary aromatic amines or ammonia stronger bases
Primary aromatic molecules are weaker bases than ammonia
43
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
44
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
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what can we use to compare relative base strengths of amines?
Pka values
46
Stronger bases have ...? pKa values
Higher
47
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)
48
How can we calculate the pKa from Ka?
-log[Ka]
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what equilibrium does pKa values refer to?
RNH3+ ----> RNH2 + H+
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Preparing Primary amines
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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)
52
Draw out the reaction to form a primary amine from 1-iodopropane
butanenitrile formed which is then reduced to form butylamine
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How are Primary aromatic amines formed?
usually made by the reduction of nitro compounds
-but can also be reduced from a Benzonitrile to Phenylmethylamine
54
What reagent is not powerful enough to reduce CN group?
NaBH4 but LiBH4 is!!!
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How can nitro groups be reduced?
1. catalytic hydrogenation (H2/ Ni catalyst)
2. using metal acid combinations (e.g Sn/Fe and HCL )
56
Show the reduction of nitrobenzene and 3-nitro 1-phenylethanone
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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)
58
what are the uses of primary aromatic amines?
- very useful intermediate in organic synthesis
- used to make synthetic dyes (azo dyes)
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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)
60
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
61
Draw out the full reaction mechanism to show how chloropropane reacts with ammonia to form a primary amine
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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
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what does this primary amine form when reacted with another haloalkane?
a secondary amine is formed via nucleophilic substitution
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the secondary amine product then goes..?
and attacks another haloalkane molecule via nucleophilic substitution to make a tertiary amine
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the tertiary amine formed then goes..?
Attacks another haloalkane via nucleophillic substitution
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What product is made?
a quaternary ammonium salt
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why can this not behave as a nucleophile?
no lone pair on the nitrogen atom so cannot behave as a nucleophile
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what is the shape of this Cation?
the cation has a tetrahedral shape
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what are the uses of quaternary ammonium salts?
used as cationic surfactants in fabric conditioners and hair products
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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.
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what do quaternary ammonium salts that are used for cationic surfactants usually have?
usually have 2 long alkyl chains and 2 short alkyl chains
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controlling the products of the reaction of ammonia
Subheading
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what is formed when Haloalkane reacts with ammonia?
a mixture of products is usually formed
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How can the mixture be separated?
with difficulty
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How is the possibility of further substitution reduced and a higher yield
if a large excess of ammonia is used
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How is a high yield of quaternary ammonium obtained?
By using a large excess of haloalkane
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Amines and ammonia as nucleophiles
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amines and ammonia act as..?
Nucleophiles
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what are nucleophiles?
nucleophiles have a lone pair of electrons that they can donate to form a covalent bond
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Amines and ammonia undergo?
1. nucleophilic substitution reactions with haloalkanes
2. nucleophilic addition-elimination reaction with acyl chlorides and acid anhydrides
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Amines and ammonia undergo what reaction with acyl chlorides and acid anhydrides?
Nucleophilic-addition-elimination reactions
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Ammonia and amines undergo nucleophilic substitution reactions with haloalkanes
Title
83
when haloalkanes are warmed with an excess of ammonia in a sealed container, what is formed?
primary amines are formed as the major product
84
what is formed when 1-chloropropane reacts with Ammonia?
Draw the word equation
CH3CH2CH2CL + 2NH3 ---> CH3CH2CH2NH2 + NH4CL
85
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
86
draw the mechanism to show how 1-chloropropane reacts with ammonia
87
what primary amine is formed?
CH3CH2CH2NH2 (1- aminopropane)
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why can primary amines act as nucleophiles themselves?
primary amines have a lone pair of electrons on the nitrogen atom
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the primary alkane can go on to react with another 1-chloropropane to make..?
a secondary amine (CH3CH2CH2)2NH - N-propylaminopropane and (propylammonium chloride)
90
Draw the next part of the mechanism to show the further substitution reaction between 1-aminopropane and haloalkane
91
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
92
what is formed?
a tertiary amine (CH3CH2CH2)3N - N,N-dipropylaminopropane and (CH3CH2CH2)2NH2CL (Dipropylammonium chloride)
93
this tertiary amine can go and react with more haloalkane to form..?
a quaternary ammonium salt (CH3CH2CH2)4N+ CL-
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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
95
controlling the products of reaction of ammonia with a haloalkane
title
96
when is multiple substitution favoured?
if there is an excess of haloalkane
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formation of a secondary amine is favoured if there is an excess of..?
Haloalkane
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when is the formation of the tertiary amine favoured?
if there is an excess Haloalkane
99
Ammonia and amines undergo nucleophilic addition-elimination reactions with acyl chlorides and acid anhydrides
title
100
draw out the word equation to show how ethanoyl chloride reacts with ammonia?
ethanoyl chloride + ammonia --> ethanamide + ammonium chloride
CH3COCL + 2NH3 --> CH3CONH2 + NH4CL
101
draw the mechanism to show the above reaction
102
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-
103
Draw the mechanism to show the above reaction
104
what are primary aromatic amines used to make?
synthetic dyes (azo dyes)
105
what are the uses of quaternary ammonium salts?
are used as cationic surfactants in fabric conditioners and hair products
106
amines are used to make polymers such as..?
polyurethanes and polyamides
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what are examples of polyurethanes?
cavity wall insulation, lycra etc
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what are examples of polyamides?
nylon fibres for clothes, carpets, toothbrushes
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what are other uses of amines?
used to make many drugs such as pethidine a painkiller
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Organic synthesis
111
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
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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
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How many steps can an organic synthesis question have?
several steps
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why do chemists design specific synthetic routes?
chemists try to design synthetic routes that use non-hazardous starting material
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why do chemists use non-hazardous starting materials?
to make processes safer and also to reduce any impact on the environment
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what else do chemists try to use?
also try use steps that do not require a solvent
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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
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what do chemists aim to design?
chemists aim to design production methods that have high atom economies and high percentage yields
119
why is this?
such processes convert more of the starting materials into useful products and are less wasteful
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For the following questions, outline and draw out the mechanisms and state the reaction conditions needed
121
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