4.6 Amines Flashcards
1
Q
Define an amine
A
- compound containing NH2 group
2
Q
Draw a primary amine
A
3
Q
Draw a secondary amine
A
4
Q
Draw a tertiary amine
A
5
Q
Draw ammonium salt
A
6
Q
Draw an amide
A
7
Q
What is the indication for a secondary amine?
A
N
8
Q
What is the indication for a tertiary amine?
A
N,N
9
Q
What are the 2 methods of forming amines?
A
- halogenoalkanes using nucleophilic substitution
- reduction of a nitrile
10
Q
Draw the formation of a primary amine using bromoethane
A
- NH3 as reagent
11
Q
Draw nucleophilic substitution to form secondary amine from bromoethane
A
- primary amine as reagent
12
Q
How do you form aromatic amines?
A
Reduction of nitrobenzene
13
Q
Draw mechanism for reduction of nitrobenzene including reducing agents
A
- tin, conc HCl, NaOH
14
Q
Why can’t nucleophilic substitution be done on chlorobenzene?
A
- Cl repels the lone pair
- C-Cl is a really strong bond because the delocalised electrons in the benzene ring repel the lone pair on the incoming nucleophile
15
Q
Weakest to strongest bases of the amines
A
- aromatic
- ammonia
- primary
- tertiary
- secondary
16
Q
Why can amines be described as bases?
A
- they have a lone pair
- by Bronsted-Lowry definition - they accept protons
17
Q
Why are aromatic amines such weak bases?
A
- electron density pulled into the aromatic ring due to delocalised electrons
- lone pair on the nitrogen is less readily available to react and form a coordinate bond
18
Q
Why are tertiary amines the second strongest base?
A
- alkyl groups crowd the nitrogen so its lone pair is not as available to bond
19
Q
Why are secondary amines the strongest base?
A
- alkyl groups push electron density toward nitrogen, making the lone pair more available
—> positive inductive effect
20
Q
Describe the impact of alkyl chains on boiling points of primary amines
A
- as alkyl chain length increases, boiling temp increases
- more VdW need breaking therefore more energy is required
21
Q
Describe the trend in boiling points of secondary amines
A
- boiling point of SA is lower than its corresponding PA
—> fewer hydrogen bonds can form due to there being only one hydrogen atom available on the nitrogen atom for bonding
—> weaker VdW, less H bonds, therefore lower boiling point
22
Q
Boiling points of amines vs alkanes
A
- amine is higher than corresponding alkane
- NH bond enables hydrogen bonding and VdW whereas alkenes just have VdW
23
Q
Boiling points of amines v alcohols
A
- amines have lower boiling point than their corresponding alcohol
- nitrogen is less electronegative than oxygen so the hydrogen bonds between amine molecules are weaker than those between alcohol molecules
24
Q
Describe the trend in solubility in amines
A
- smaller amine chain makes it more soluble
- form hydrogen bonds between lone pairs in H2O and the hydrogen on amine
- tertiary amines less soluble as the nitrogen atom is overcrowded so less available to form a hydrogen bond
25
Draw 1,4-diaminobutane hydrogen bonding in water
26
How do you maximise the amount for primary amines formed from nucleophilic substitution?
- excess ammonia
27
How do you maximise the formation of quaternary salts?
- excess halogenoalkanes
28
Draw the reduction of nitrile including the reducing agents
- LiAlH4 dissolved in ether
29
Why can an amide act as a base?
It contains a nitrogen atom that has a lone pair of electrons and is a proton acceptor
30
Draw the functional groups of an amide and acid chloride
31
What are the 3 reactions of amines?
- ethanoylation
- nitric acid
- benzenediazonium
32
Draw the addition elimination reaction for ethanoyl chloride (ethanoylation)
- amines act as nucleophile due to the lone pair on the nitrogen atom
- attack the positive carbon in the carbonyl group in an acid chloride to form an amide
33
What reagent is used to produce an amide from an amine?
X-oyl chloride
(ie pent, eth, meth etc)
34
Draw the mechanism for the production of an amine and carboxylic acid from anhydrides
35
What is meant by a chromophore?
Part of the a molecule responsible for colour
36
Equation for the formation of nitrous acid
NaNO2 + HCl —> HNO2 + NaCl
37
What happens when nitrous acid reacts with aliphatic amines?
Forms an alcohol
—> R-NH2 + HNO2 —> R-OH + N2 + H2O
38
What happens when nitrous acid is reacted with aromatic amines?
Forms a solution containing benzenediazonium ions
39
Describe a test to differentiate between aliphatic and aromatic amines
- add nitrous acid below 10°C
- if N2 is seen, it is a primary aliphatic amine
- if no N2 is seen, it is an aromatic amine
40
What happens to a benzenediazonium ion above 10°C?
It decomposes to phenol and nitrogen
41
Draw mechanism for the coupling reaction of phenol and an aromatic amine
42
Describe the inductive effect of benzene rings
- draw electron density away from, the nitrogen atom, making the lone pair less available
43
Describe the inductive effect of alkyl groups
- push electron density towards the nitrogen making the lone pair more available
—> aliphatic amines stronger bases than aromatic
44
State the reagents and conditions in the synthesis of a diazonium ion from an aromatic amine
- HNO2 and HCl
- less than 10°C
- react with phenol in alkaline conditions
45
Inorganic compound formed from the mixture of HCl and NaNO2
HNO2
46
Describe the stages in the manufacture of methylphenylamine from benzene
- methylation
—> CH3Br
—> AlCl3 catalyst
—> C6H5CH3 + HBr
- nitration
—> conc H2SO4
—> conc HNO3
—> C6H4(CH3)NO2
- reduction
—> tin and HCl
—> C6H4(CH3)NO2
47
Reagent that will convert OH group to O-
NaOH
48
Reagents and conditions to go from nitrobenzene to aminobenzene
Tin and HCl
49
Explain how the amino groups in primary amines such as 1,4-diaminobenzene allow it to act as a base
- lone paid on nitrogen accepts protons
- forming dative covalent bond
50
Why is hexane-1,6-diamine a strong base?
- electrons move toward the N due to electron density
- lone pair is delocalised
- H+ more easily accepted
51
Why do amines have lower boiling points than their corresponding alcohol?
- nitrogen is less electronegative than oxygen so forms weaker hydrogen bonds
