Chapter 27 - Amines, Amino Acids and Polymers Flashcards
define what an amine is
“Amines are organic compounds derived from ammonia in which one or more hydrogen atoms in ammonia have been replaced by a carbon chain or ring”
what is the difference between primary/secondary/tertiary amines
primary = 1 alkyl/acyl group is substituted secondary = 2 alkyl/acyl groups are substituted tertiary = 3 alkyl/acyl groups are substituted
how to name amines where a single hydrogen has been replaced by a straight/branched carbon chain
if at the end of a chain simply add amine e.g. butylamine
if at a point other than the end on the chain add a number and amino e.g.
2 aminobutane
how to name amines where two or more hydrogens have been replaced by the same type of carbon chain
add di… or tri…
e.g. dimethylamine
how to name amines where 2 or more different groups are substituted for hydrogens
do N - smaller group, bigger group amine
e.g.
N-methyl propylamine
what is the main way that amines can react and why
- they can react by acting as a base, they contain a lone pair on the nitrogen that is able to accept a proton to form a daitive covalent bond, producing an ion
what occurs when an amine reacts with an acid
- they act as a base to neutralise the acid
- the NH2 goes to NH3+ and bonds with the anion of the acid
how can we prepare aliphatic amines, state the conditions
1) react a haloalkane with ammonia to form an alkyl ammonium salt (like in the salt-acid reactions)
2) react the salt formed with excess aqueous alkali e.g. NaOH to form a primary amine and other products (often salt and water)
conditions:
1) use ethanol as a solvent
2) use excess ammonia
explain why we use these conditions in the production of aliphatic amines
1) we use ethanol as a solvent to prevent the hydrolysis of haloalkanes to alcohols
2) we use an excess of ammonia to prevent further substitutions of the primary amine
explain what occurs in the preparation of primary amines/ what sort of mechanism it is
- ammonia can act as a nucleophile in a substitution reaction as it can donate its lone pair
- so it is nucleophilic substitution
explain why this reaction is not suitable for producing pure primary amines
once the first substitution has taken place to form a primary amine, the N atom still has a lone pair, this can further react with the haloalkanes to form a secondary amine, this can occur again to form a tertiary amine
explain the method for producing aromatic amines
- reduce nitrobenzene using concentrated hydrochloric acid and a tin catalyst
- the nitrobenzene and conc HCl act as a reducing agent [H]
- then react the salt formed with excess alkali to form an amine
C6H5NO2 + 6[H] —–> C6H5NH2 + 2H2O
define an amino acid
“Amino acids are organic compounds containing both the amine, NH2, group and the carboxylic acid, COOH, group”
explain what an Alpha amino acid is
where the amine group is attached to the 2 carbon, the alpha carbon, i.e. the carbon adjacent to the carboxylic acid group
they have the general formula
RCH(NH2)COOH
what do amino acids form in acidic solutions
- positive ions
- NH2 acts as a base and forms NH3+
- this can form salts as amines usually do
what do amino acids form in alkaline solution
- negative ions
- COOH acts as an acid and forms COO-
- this can also form a salt (and sometimes water)
how do amino acids react with alcohols and how is this different to carboxylic acids
- they form esters just like carboxylic acids
- but because this reaction is done in the presence of a conc. H2SO4 catalyst, they also form NH3+ on the amino group
what are the 4 main things to remember about Zwitterions
- at intermediate pHs (isoelectric points), Zwitterions form
- the exact pH depends on the amino acid
- these have both positive and negative charges on different parts of the molecule as the NH2 group acts as a base and the COOH group acts as an acid
- they have ionic bonding due to the opposite charges
define stereoisomerism
“stereoisomers are molecules/compounds with the same structural formula but a different arrangement in space”
where is optical isomerism found in amino acids/amine type molecules
optical isomerism:
- found in molecules with a chiral centre
- chiral centre is a carbon that is attached to 4 different groups
- leads to 2 non-superimposable mirror images of each other
- for each chiral centre there is a pair of optical isomers
what is the difference between an amine and an amide
- in an amide the carbon attached to the Nitrogen also attaches to a oxygen
- in an amine it doesn’t
how can we form primary and secondary amides
Acyl chloride + ammonia —> Primary amide + HCl
Acyl chloride + primary AMINE —> secondary amide + HCl
what on the R group of an amino acid might affect its isoelectric point
- a carboxylic acid group will make the isoelectric point more acidic
what is the isoelectric point of an amino acid
- the point at which the amino acid group acts as both a base and an acid
- NOTE: the amino acid at the isoelectric point is always neutral, meaning any other groups on the R group don’t react
what are the two types of polymerisation and generally which types of molecules undergo which polymerisation
- addition polymerisation – alkenes
- condensation polymerisation – carboxylic acids and their derivatives
what are the two main types of condensation polymers
polyamides
polyesters
define condensation polymerisation
“Condensation polymerisation is the joining of monomers to form a long chain polymer with the loss of a small molecule, usually water”
define a polyester
“a type of condensation polymer containing an ester linkage, RCOOR”
what are the two ways to make polyesters
- from one monomer – this monomer contains both a carboxylic acid (COOH) group and an alcohol (OH) group
- from two monomer – one monomer contains two carboxylic acid (COOH) groups and one monomer contains two alcohol (OH) groups
what is an example of a polyester formed from one monomer, draw it
- polyglycoic acid, HOCH2COOH is the monomer
- O - CH2 - CO - O - CH2 - CO - O - etc.
the repeat unit is the O-CH2-CO part
what is an example of a polyester made from two monomers, draw it
Terylene, formed from
Benzene - 1,4 - dicarboxylic acid
Ethane - 1,2 - diol
- CO - (C6H4) - CO - O - (CH2)2 - O -
is the repeat unit despite being formed from 2 monomers
define a polyamide
“a type of condensation polymer when monomers are joined to form a polymer by amide linkages”
what are the two ways that polyamides can be formed
- by one monomer – containing both a carboxylic acid/acyl chloride group and an amine group
- by two monomers – one monomer contains two carboxylic acid/acyl chloride groups, one monomer contains two amine groups
give an example of a polyamide formed from one monomer, what are they generally made of, draw it
- amino acids contain both a carboxylic acid and amine group so can form polyamides
- they undergo condensation polymerisation
H2N - CH(CH3) - COOH is a suitable monomer
- NH - CH(CH3) - CO -
is a repeat unit
give an example of a polyamide formed from 2 monomers, draw it
- both Kevlar and Nylon are formed this way
- Nylon (6,6) is formed from 1,4 Hexandioc acid and 1,6 diaminohexane
- NH - (CH2)6 - NH - CO - (CH2)4 - CO -
is the repeat unit despite being two monomers
(note: these can also be made with the carboxylic acids’ respective acyl chlorides but HCl is formed not water)
what are the two ways condensation polymers can be hydrolysed, give the conditions
- Acid or Alkali
- Acid hydrolysis = HOT AQUEOUS acid (HCl)
- Alkali hydrolysis = HOT AQUEOUS alkali (NaOH)
this is the same way as esters
what are the reactions of a polyester in acid and alkali hydrolysis
alkaline
polyester + NaOH/H2O (HOT) —> Sodium Carboxylate salt/carboxylate ion + alcohol
( or equivalent product for a single monomer)
acidic
polyester + H+/H2O (HOT) —> carboxylic acid + alcohol
(or equivalent for a single monomer)
what are the reactions of a polyamide in acid and alkali hydrolysis
alkali
polyamide + NaOH/H2O (HOT) —> sodium carboxylate salt/carboxylate ion + amine
(or equivalent for single monomer)
acid
polyamide + H+/H2O (HOT) —> carboxylic acid + amine(with NH3+ not NH2)
(or equivalent for single monomer)
what to always remember when drawing polymers
always draw the linkages (ester or amide) because even if the rest is wrong, that will get a mark
what type of reaction is the formation of phenylamine from nitrobenzene
reduction
what to be specific about when explaining why an NH2 group acts as a base
THE LONE PAIR ON THE NITROGEN accepts a proton…
give two reasons why polyamides and polyesters are more likely to biodegrade than addition polymers
- the C=O bond can absorb radiation and break
- the ester/amide linkage can be hydrolysed
why might planar polymers have a higher melting/boiling point than non-planar polymers
they can pack together more and thus have greater London forces
what to remember when writing about hydrolysis of polymers
Heat (reflux), and NAME THE DILUTE ACID
how would you make an aromatic secondary amide
phenylamine (and derivatives) with an acyl chloride
