PL2 - The Nylon Story Flashcards
What are amines?
Homologous series resembling ammonia.
1, 2, or 3 of the hydrogen groups are replaced by alkyl groups however
What are primary amines?
Amines with one alkyl group
How are primary amines named?
Where there might be confusion about where the -NH2 group is attached to a chain, they are named using the “amino” form.
E.g. 2-amino propane
Unless methyl or ethyl amine
Which type of amine is used to make condensation polymers?
Diamines
What are secondary amines?
Amines with two alkyl groups
(2 Hs of ammonia have been replaced)
What are tertiary amines?
Amines where all three hydrogens of ammonia are replaced with alkyl groups
What are quaternary amines?
They don’t exist!
This is an ammonium ion, NH4+
How are secondary amines named?
By adding the name of the alkyl chain to ‘amine’ (usually with di-)
E.g. dimethylamine
In more complex ones, both alkyl chains named alphabetically
E.g. Ethylpropylamine
(Not likely to be given more complex ones in exam)
How are tertiary amines named?
Similarly to secondary amines - add prefix of alkyl group and usually tri-
E.g. Trimethylamine
More complex ones might be: Diethylmethylamine
(Not likely to come across more complex ones in exam)
What are diamines?
Amines with two amino group attached
(AKA alkyl chains with two amino groups)
How are diamines named?
Named after the partent alkane with the prefix diamino- (and numbered)
E.g. 1,6-diaminohexane
How are branched diamines named?
The same as normal diamines but the branched alkyl group prefix is added after
E.g. 1,5-diamino-2-methylpentane
What state are amines with a low relative molecular mass in at standard conditions?
Gases/volatile liquids.
How do volatile amines resemble ammonia?
Not only are they volatile but they also have strong smells like rotting fish or flesh in general
They also have similar chemical properties
What properies is the lone pair in amines responsible for?
Their solubility in water and acting as bases
How is the bonding in amines similar to that of ammonia?
Both contain a lone pair
The remaining 3 bonds are localised covalent between either alyl groups or hydrogens
Why are amines soluble in water?
They have a lone pair on a hghly electronegative atom (nitrogen) and also have hydrogens bonded to it.
This means they can form hydrogen bonds with water molecules
Why are larger amines (amines with larger alkyl groups) not as soluble in water (if at all)?
The large alkyl grups are less able to break the H-bonds between water molecules.
Because the enthalpy change to break these bonds > enthalpy change in formation of new bonds between alkyl groups + water
Why are amines able to act as bases?
The lone pair on the nitrogen atom forms a dative covalent bond with H+ (by donating the electron pair)
This leaves an OH- making the solution alkaline
What does the strength of an amine as a base depend upon?
The availability of the lone pair to bond with H+
The stability of the positive ion formed
The solubility of the amine and steric hindrance
How do amines react with acids?
The amine accepts a H+ to form an alkyl-ammonium ion (e.g. ethylammonium) and water.
The reaction goes to completion
How do amines react with water?
An alkyl-ammonium ion is formed as well as OH-
The reaction does not go to completion, instead reaching equilibrium
Why do reactions between amides and acids go to completion but those between amines and water don’t?
Because the H3O+ ions in acidic solutions are more powerful H+ donors than water
How can you tell that the reaction between an amine and an acid has gone to completion?
It loses its characteristic smell
Why does having more alkyl groups make an amine more basic?
Alkyl groups tend to donate electrons and do so to the nitrogen.
This makes the lone pair more accessible and reduces steric hindrance.
What is the general formula for primary amides?
What is the general formula for secondary amides?
What are amides?
Carboxylic acid derrivatives where the -OH group is replaced with -NH2
How are amides made and why?
By reacting ammonia/amines with acyl chloride.
Carboxylic acids cannot be used as they don’t react to give amides
What type of reaction occurs between ammonia/amines and acyl chloride?
What are the by-products?
A condensation reaction
The small molecule produced is HCl
What type of amide does reacting ammonia and acyl chloride produce?
Primary amides
What type of amide does reacting an amine and acyl chloride produce?
Secondary amides
Why is condensation polymerisation called that?
Because the individual steps joining the molecules together are condensation reactions
How are polyamides made and what links the monomers together?
Reacting a dicarboxylic acid and a diamine
The monomers are linked together by amide groups
Why are polyamides called that?
Because the monomers are linked together by secondary amide groups
What is another name for polyamides?
Nylons
Why are acyl chlorides used instead of carboxylic acids when making nylons in the lab?
Because the reaction is slow otherwise and it is hard to demonstrate the process
How are nylons named?
According to the number of carbon atoms in the monomers
The 1st digit is the no. in the diamine, the 2nd is the dicarboxylic acid
(This applies if 2 monomers are used)
(Think: a comes 1st, c 2nd)
If a nylon only has 1 number after it what does that mean?
It has only been made from one monomer containing a diamide at one end and a dicarboxylic acid at the other
What are acyl chlorides?
More reactive derrivatives of carboxylic acids
What is the general formula of acyl chlorides?
How are acyl chlorides named?
By replaicing the -oic with -oyl and ‘acid’ with ‘chloride’
How are diacyl chlorides named?
Adding -dioyl instead of just -oyl
How do acyl chlorides react with amines?
Vigourously to form amides:
RCOCl + R’NH2 → RCONHR’ + HCl
How do acyl chlorides react with alcohols?
Vigourously to form esters:
CH3OH + C2H5COCl → C2H5COOCH3 + HCl
(Propanoyl chloride + methanol → methyl propanoate + hydrochloric acid)
