Ch6.2 Nitrogen compounds, polymers and synthesis Flashcards
1
Q
What molecule are amines related to?
A
ammonia
2
Q
What are amines essentially?
A
organic molecules in which one or more of the H atoms in ammonia have been replaced by an alkyl chain
3
Q
What are primary amines?
A
- only one H atom has been replaced by an alkyl chain
4
Q
What are secondary amines?
A
- 2 H atoms have been replaced by alkyl chains
5
Q
What are tertiary amines?
A
- all 3 H atoms have been replaced by alkyl chains
6
Q
How are primary amines named?
A
- the root is the longest carbon chain
- the suffix is ‘amine’
- any side groups are added alphabetically as prefixes
- numbers for prefixes are determined by counting away from the N
7
Q
How are secondary amines named?
A
- name both alkyl chains
- the longest chain is the root of the name
- ‘amine’ is suffix
- name side groups and add them as prefixes
8
Q
How are tertiary amines named?
A
- name all 3 alkyl chains
- longest chain is the root
- if there’s identical alkyl groups, use ‘di’ or ‘tri’
9
Q
What can amines act as and why?
A
- amines can act as bases (proton acceptors)
- amines can act as nucleophiles (they can donate a lone pair of electrons to a region of positive charge)
- amines can do both of these things due to the lone pair of electrons on the nitrogen atom
10
Q
When amines react with acids as bases, what organic molecule is produced?
A
- ammonium salt
11
Q
How can amines be produced?
A
- by reacting ammonia with haloalkanes
12
Q
Describe the 2 stage reaction used to produce amines
A
- an ammonia molecule reacts with a haloalkane to make an ammonium salt
- a second ammonia molecule reacts with the ammonium salt produced in stage 1. This produces a primary amine and ammonium chloride
stage 2 is reversible
13
Q
How is the equilibrium of the second stage of producing an amine driven to the product side?
A
add excess ammonia
14
Q
Which 2 functional groups are amino acids guaranteed to have?
A
- amine group
- carboxylic acid group
15
Q
What are polymers?
A
- long-chain molecules made from smaller molecules (monomers) linked together
16
Q
What are the 2 types of polymers?
A
- addition: the monomers link together to make a single product
- condensation: the monomers link together to make a polymer and one other product (usually water)
17
Q
What must the monomers of addition polymers have?
A
C=C bond
18
Q
What are the 2 types of condensation polymers?
A
- polyesters
- polyamides
19
Q
What are the monomers of polyesters?
A
- dicarboxylic acid
- diol
20
Q
What are the monomers of polyamides?
A
- dicarboxylic acid
- diamine
21
Q
Give an example of a polyester
A
poly(lactic acid)
22
Q
Give an example of a polyamide
A
nylon
23
Q
What is the monomer and use of poly(ethene)?
A
- ethene
- carrier bags
24
Q
What is the monomer and use of poly(chloroethene)? aka PVC
A
- chloroethene
- rulers, cling film, pipes, window frames
25
What is the monomer and use of poly(propene)?
- propene
- ropes, crates, storage boxes
26
What is the monomer and use of poly(ethylbenzene)? aka polystyrene
- ethylbenzene
- food packaging, cups
27
How are esters formed?
- when an alcohol reacts with a carboxylic acid
28
What kind of reaction is simple esterificatio
- reversible
- condensation (water is eliminated)
29
How are esters named?
- alcohol first (yl)
- carboxylic acid last (oate)
30
How must you change the reactants for esterification to result in a polyester rather than an ester?
- the monomers must be a diol and a dicarboxylic acid
(instead of an alcohol and a carboxylic acid)
31
How is poly(lactic acid) formed?
- lactic acid is a natural monomer with both an alcohol group and a carboxylic acid group
32
What is the polymer of amino acid monomers?
- proteins/polypeptides
33
When do amide linkages form?
- when an amine group reacts with a carboxylic acid group
34
What are the monomers of a polyamide?
- diamine
- dicarboxylic acid
35
During polymerisation, when are 2n H2O molecules formed rather than just n?
- when diamines, diols or dicarboxylic acids are used
36
How do proteins (formed from amino acids) and polyamides (formed from diamines and dicarboxylic acids) differ in their bonding?
- in proteins, all amide links have the same orientation
- ie. CONH, CONH, CONH
- in polyamides, amide links have alternating orientations
- ie. CONH, NHCO, CONH, NHCO
37
Describe ethene polymerisation
1- initiation.
H-O-O-H --> 2 'O-H (radicals)
(using UV light)
2- propagation.
H-O' + C2H4 --> CH2OHCH2'
CH2OHCH2' + C2H4 --> CH2OHCH2CH2CH2'
and so on...
3- termination.
CH2OHCH2' + CH2OHCH2' --> CH2OHCH2CH2CH2OH
38
What is a nylon?
- a polyamide in which the monomers are straight chain
39
How are nylons named?
- nylons are named uniquely
- eg. Nylon- 3,4 is made of a diamine with 3 carbons and a dicarboxylic acid with 4 carbons
40
How are aliphatic amines formed?
- heating a haloalkane and excess ammonia in ethanol (solvent)
- this is done in a sealed container and not under reflux as ammonia is very volatile
- this prep method will always produce a mixture of primary, secondary, tertiary and quaternary ammonium salts
41
What type of reaction is the reaction between excess ammonia and haloalkanes to form aliphatic amines?
- nucleophilic substitution
42
How is production of the primary amine favoured in the production of aliphatic amines?
- add excess ammonia
43
How are aromatic amines produced?
- by the reduction of nitroarenes
44
What is the reducing agent for producing aromatic amines from nitroarenes?
- it's formed in situ using tin (source of electrons) and conc HCl under reflux at 100 degrees C
45
What are the 2 stages of reaction for forming aromatic amines from nitroarenes?
- the reaction initially forms the phnylammonium salt
- this salt is then reacted with sodium hydroxide to remove the hydrogen ion and excess HCl
46
After the reaction for the production of aromatic amines from nitroarenes, how is the amine separated?
- steam distillation
- solvent extraction
- more distillation
47
Why are amino acids amphoteric?
- they have an acidic carboxyl group and a basic amine group
48
What are the 2 types of stereoisomers?
- optical isomers
- E/Z isomers
49
What is optical isomerism?
- when 2 molecules are chemically identical but they cannot be super-imposed on top of one another
- they're mirror images
- they react with polarised light differently
50
What properties are similar and different in enantiomers?
- similar physical properties
- same chemical properties
- different biological properties
51
What is an example of a pair of enantiomers that have different biological properties?
- limonene
- a chiral hydrocarbon found in citrus fruit
- one enantiomer smells strongly of oranges
- the other enantiomer smells of pine
52
What do the prefixes of + and - mean on enantiomers?
- this is the effect the enantiomer has on a plane of polarised light
- if the enantiomer rotates the plane of polarised light clockwise then its prefix is +
- if it rotates the plane of polarised light anti-clockwise then its prefix is -
- prefixes can only be deduced by experiment, not from the structures
53
What is a 50:50 mixture of enantiomers known as?
- a racemate
- or a racemic mixture
54
What effect will a racemic mixture have on polarised light?
- no effect
- the rotations of the two isomers cancel each other out
55
What is the condition for optical isomers to be formed?
- the molecule must have a chiral centre
56
What is a chiral carbon or a chiral centre?
- a carbon atom with 4 different groups attached
57
What is hydrolysis?
- hydrolysis is the chemical reaction in which water breaks bonds
58
What is produced during hydrolysis of condensation polymers?
- the monomers
59
Why do condensation polymers, eg. nylon, not degrade when it rains?
- hydrolysis of polyesters and polyamides has a very slow rate of reaction
60
How can you hydrolyse condensation polymers faster than just using water?
- in acidic or basic conditions
- the rate can be increased even further by heating the reaction mixture
61
Is acidic or basic hydrolysis of polyesters faster?
- basic hydrolysis of polyesters is much faster
- acidic hydrolysis has a slow rate of reaction
62
Describe the process of acidic hydrolysis of polyesters?
- polyester reacted with strong aqueous acid
- reaction produces a diol and a dicarboxylic acid
SLOW RATE OF REACTION
63
Describe the process of alkali hydrolysis of polyesters
- polyester reacted with hot NaOH solution
- produces diol and salt of the carboxylic acid
FAST RATE OF REACTION
64
Is acidic or basic hydrolysis of polyamides faster?
- acid hydrolysis of polyamides is much faster
65
Describe the process of acid hydrolysis of polyamides
- polyamide reacted with strong aqueous acid
- produces a diammonium salt and a dicarboxylic acid
66
Describe the process of alkali hydrolysis of polyamides
- polyamide is reacted with hot NaOH solution
- produces the diamine and the salt of the dicarboxylic acid
67
What is the difference between cyanide and nitrile?
- CN- ion is known as the cyanide ion
- when the CN group is found in an organic chemical it becomes known as a nitrile functional group
68
Is cyanide a nucleophile or an electrophile?
- nucleophile
- attracted to areas of positive charge in a molecule
69
Which organic molecules are susceptible to attack by nucleophilic attack of a cyanide ion and why?
- haloalkanes
- C-X bond has a dipole due to difference in electronegativity between carbon and halogen
70
What conditions and reagents are needed for nucleophilic substitution of a cyanide ion on a haloalkane?
- haloalkane mixed with potassium cyanide
- heated under reflux
- ethanol used as a solvent to ensure the nucleophile is the cyanide ion
71
Why is ethanol used as the solvent for extending carbon chain length using cyanide ions on haloalkanes and not water?
- ethanol as a solvent ensures the nucleophile is the cyanide ion
- if water is used, the hydroxide ion tends to be the nucleophile and the carbon chain length would not increase
72
What is the mechanism for extending the carbon chain length using cyanide ions and haloalkanes?
nucleophilic substitution
- cyanide takes the place of the halogen
73
Other than haloalkanes, what kind of organic molecules are susceptible to nucleophilic attack?
- carbonyls
- in C=O bond, the carbon has a slight positive charge which nucleophiles can attack
74
How does cyanide react with carbonyls?
- hydrogen cyanide is used to generate the cyanide nucleophile
- cyanide ion is attracted to the carbon of the carbonyl group and forms new covalent bond
75
What does cyanide + carbonyl result in and why?
- hydroxynitrile
- the pi bond of the C=O opens and the oxygen accepts the pair of electrons
- oxygen is then negatively charged and so accepts a proton and becomes an OH group
76
How does cyanide + (some) carbonyls result in a racemic mixture?
- the C=O bond is planar
- equal chance of which side the nucleophile may attack from
77
Which carbonyls will produce a racemic mixture when reacted with cyanide?
- asymmetric ketones
- any aldehyde other than methanal
78
In labs, is HCN or KCN more commonly used and why?
- HCN is a highly toxic gas in normal lab conditions
- KCN is a cyanide salt and is much safer in labs
- KCN is solid at room temp and is easier to handle
79
How must KCN be used if it is used for the reaction of extending carbon chain length?
- the salt must be in an acidified solution so both CN- and H+ ions are present
80
What is formed when nitriles are reduced?
- amines
81
Can hydrogen gas react directly with a nitrile and if so what happens?
- hydrogen gas can react directly with a nitrile to form a primary aliphatic amine in the presence of a nickel catalyst
- 2 hydrogen atoms are added to the nitrogen atom of the nitrile group
82
Does the reduction of a nitrile require a catalyst?
- yes
- nickel catalyst
83
How is the rate of reaction increased when reducing nitriles?
- nickel catalyst lowers activation energy to enable reaction to occur
- mixture is heated to 150 degrees C at raised pressure
84
What are the conditions and reagents for typical reduction of nitriles?
- nickel catalyst
- 150 degrees C
- raised pressure
- H2
85
What is an alternative method of reducing nitriles other than using hydrogen gas?
- using a reducing agent such as lithium tetrahydridoaluminate(III), LiAlH4
85
What is formed when nitriles are hydrolysed?
- initially forms an amide
- then forms an ammonium salt
- second reaction to form an ammonium salt is so slow that it isn't significant
86
How can the rate of reaction for the hydrolysis of nitriles be increased?
- strong acid catalyst
- heat under reflux
87
How does normal hydrolysis and acid hydrolysis of nitriles differ?
- normal hydrolysis produces an amide and then an ammonium salt (slow)
- acid hydrolysis produces carboxylic acids
88
If a nitrile undergoes acid hydrolysis, a carboxylic acid and an ammonium salt are formed. Why is an organic acid formed and not an organic ammonnium salt?
- the strong acid ionises fully in solution forming H+ and Cl- ions
- when the amide has formed, the C-N bond breaks, making a carboxylate ion
- carboxylate ion reacts with proton from the strong acid to make a carboxylic acid
- organic acids are weak and would only partially ionise in solution
89
What is the mechanisms for substitution reactions of arenes and how are these reactions facilitated?
- electrophilic substitution
- catalyst needed such as AlCl3 or FeCl3
90
What are the 2 types of substitution reaction in aromatic compounds?
- alkylation
- acylation
91
What are the reagents for alkylation of an aromatic compound?
- an aromatic compound
- haloalkane
- strong Lewis acid catalyst
92
What are the conditions for benzene reacting with chloromethane and what organic compound is produced?
- FeCl3 catalyst needed
- methylbenzene produced
93
What is the mechanism for alkylation of an aromatic compound?
- electrophilic substitution
94
What occurs during acylation?
- RCO- is added to an organic compound (R is a hydrocarbon chain)
95
What are the reagents and conditions for acylation of an organic compound?
- an acyl chloride
- a strong Lewis acid catalyst
- heat under reflux
96
How do benzene and ethanoyl chloride react?
- heated under reflux
- acylation
- anhydrous AlCl3
- electrophilic substitution
97
What is the mechanism for acylation of an organic compound?
- electrophilic substitution
