Module 6 Section 2: Nitrogen Compounds, Polymers and Synthesis Flashcards
How can polymers be formed
Alkenes can form polymers by addition polymerisation or condensation polymerisation
What are two condensation polymers
Polyesters and polyamides
Where polyesters and polyamides originate from
Carboxylic acids and their derivatives are common starting materials
What is condensation polymerisation
The joining of monomers with loss of a small molecule
The small molecule usually includes water or hydrogen chloride
Two different functional groups are needed
How are monomers joined together in polyesters
Joined together by ester bonds (esterification) in a long chain to form a polymer
What do the monomers contain in polyesters
One monomer containing both a carboxylic acid and an alcohol group
Or from two monomers - one containing two carboxylic acid groups (dicarboxylic) and the other containing two alcohol groups (diol)
Example of a polyester formed from a monomer with two different functional groups
Glycolic acid contains both a hydroxyl group and a carboxyl group
It undergoes condensation polymerisation to form poly(glycolic acid) joined by ester linkages and water is released
Example of a polyester formed from two monomers each containing two functional groups
Terylene (polyethylene terephthalate or PET) is formed from the reaction between two monomers, benzene-1,4-carboxylic acid and ethane-1,2-diol
During the reaction a hydroxyl group on the diol reacts with a carboxyl group on the dicarboxylic acid forming an ester linkage and water
What are polyamides
Formed when monomers are joined by amide linkages in a long chain to form a polymer
What do the monomers contain in polyamides
Polyamides can be made from one monomer containing both a carboxylic acid (or acyl chloride) and an amine group
Or from two monomers, one containing two carboxylic acid groups (or acyl chlorides) (dicarboxylic acid) and the other containing two amine groups (diamine)
Example of a polyamide formed from one monomer with two functional groups
Amino acids contain both an amine group and a carboxylic acid group
Amino acids undergo condensation polymerisation to form polypeptides or proteins
What happens when an amide bond is formed
When an amide bond is formed the carboxyl group reacts with the amine group to form an amide linkage and water is lost (hydroxyl in COOH reacts with hydrogen in NH2)
Example of a polyamide formed from two monomers each with two functional groups
Nylon is formed from hexanedioic acid and 1,6-diaminohexane or hexanedioyl chloride and 1,6-diaminohexane
Different types of nylon can be made by varying the carbon chain length
How can polyesters and polyamides be hydrolysed
Can be hydrolysed using hot aqueous alkali such as sodium hydroxide
Or by hot aqueous acid such as hydrochloric acid
What do polyesters form when they are hydrolysed
They form a metal salt of the carboxylic acid (e.g. a dicarboxylic acid salt) and a diol
What do polyamides form when they are hydrolysed
They form a dicarboxylic acid and a diamine
How are polyesters and polyamides more easily hydrolysed
Polyamides are more easily hydrolysed with an acid than a base
Polyesters are more easily hydrolysed with a base than an acid
Characteristics of addition polymerisation
Monomer contains a C=C bond
Backbone of polymer is a continuous chain of carbon atoms
Characteristics of condensation polymerisation
Two monomers each with two functional groups
One monomer with two different functional groups
Polymer contains ester or amide linkages
Haloalkane to nitrile
NaCN or KCN Ethanol Reflux
Haloalkane to amine
Excess ethanolic NH3 (or amines)
Heat
Nitrile to amine
LiAlH4 then dilute acid
Or Na and ethanol, reflux
Or H2, Ni/Pt catalyst, high temp and pressure
Nitrile to Carboxylic acid
Dilute HCI Reflux
Hydroxynitrile to carboxylic acid
Dilute HCI Reflux
Ketone to 2° alcohol
NaBH4 then water
Aldehyde to hydroxynitrile
HCN or NaCN
Ketone to hydroxynitrile
NaCN or HCN
Hydroxynitrile to amine
LiAlH4 then dilute acid
Or Na and ethanol, reflux
Or H2, Na/Pt catalyst, high temp and pressure
Aldehyde to 1° alcohol
NaBH4 then water
Alcohol to carboxylic acid
K2Cr2O7 H2SO4 Reflux
Alcohol to ester
Carboxylic acid, H2SO4 catalyst, heat
Or acyl chloride
Or acid anhydride
Carboxylic acid to ester
Alcohol, H+ (acid) catalyst
Ester to carboxylic acid
Dilute acid or alkali
Ester to carboxylate
OH-
Heat
Acyl chloride to ester
Alcohol
20°C
Acyl chloride to carboxylic acid
Cold H2O
Carboxylic acid to acyl chloride
SOCI2
Acyl chloride to 1° amide
NH3 20°
Acyl chloride to 2° amide
Primary amine 20°
Benzene to nitrobenzene
Conc HNO3
Conc H2SO4
Warm
Benzene to halobenzene
X2
AlCl3 catalyst
Warm
Benzene to alkyl benzene
Haloalkane
AlCl3 catalyst
Reflux
Benzene to phenylketone
Acyl chloride
AlCl3 catalyst
Reflux
Nitrobenzene to phenylamine
Tin
Conc HCl
Reflux then add NaOH
Phenol to sodium phenoxide
NaOH
20°
Phenol to phenyl ester
Acyl chloride
20°
Phenol to 2-nitrophenol or 4 nitrophenol
Dilute HNO3
20°
Phenol to 2,4,6 tribromophenol
Bromine water (Br2)
20°
How do you get an amine from ammonia
If one or more hydrogen is replaced by an organic group
What determines if an amine is primary, secondary, tertiary or quaternary
This is determined by how many alkyl groups the nitrogen atom is bonded to
What do you get if the nitrogen atom is bonded to 4 alkyl groups
You get a positively charged quaternary ammonium ion
Difference between an aliphatic and aromatic amine
Aliphatic: when the amine doesn’t contain any benzene structures
Aromatic: amine contains a benzene ring
Are amines basic or acidic
Amines are bases
There’s a lone pair of electrons on the nitrogen atom of an amine that’s able to accept protons (H+ ions)
How do amines react with acids
Amines are neutralised by acids to make ammonium salts.
E.g. ethylamine reacts with HCl to form ethylammonium chloride
How to get an amine from haloalkane
Heat the haloalkane with an excess of ethanolic ammonia
Possible products of preparing an amine from a haloalkane
Get a mixture of primary, secondary and tertiary amines, and quaternary ammonium salts
More than one hydrogen is likely to be substituted.
Can separate the products using fractional distillation.
How can multiple different products be formed in stages from bromoethane reacting with ammonia
Reacts to form ethylamine
This is nucleophilic substitution
Ethylamine can then react with ammonia and bromoethane again to form diethylamine
Can continue until quaternary amine formed
How can multiple different products be formed in stages from bromoethane reacting with ammonia
Reacts to form ethylamine
This is nucleophilic substitution
Ethylamine can then react with ammonia and bromoethane again to form diethylamine
Can continue until quaternary amine formed
How to form an aromatic amine
Must reduce a nitro compound
Nitro compounds must be reduced using 2 steps
Heat mixture of nitro compound, tin and conc HCl under reflux to make a salt
Then add NaOH to get aromatic amine
What are amides
Derivatives of carboxylic acids
Contain functional group -CONH2
Why do amides behave differently from amines
The carbonyl group pulls electrons away from the rest of the -CONH2 group
What types of amides can you get
Can be either primary, secondary or tertiary amides
This depends on how many carbon atoms the nitrogen is bonded to
What functional groups do amino acids have
Amino acids have a basic amino (NH2) group and acidic carboxylic group (COOH)
Structure of an α (alpha) amino acid
This is where both groups are attached to the same carbon atom (the α (alpha) carbon)
The general formula of an alpha amino acid is RCH(NH2)COOH
How do amino acids react with alkalis
The carboxylic acid group in the amino acid can react with an alkali to form a conjugate base: RCH(NH2)COO-
This can combine with a positive ion to form a salt:
How do amino acids react with acid
The amino group can react with an acid to form a salt of the conjugate acid
E.g:
How do amino acids react with alcohols
Carboxylic acid group in an amino acid can react with an alcohol to form an ester
Requires strong acid catalyst (normally H2SO4)
What is a chiral carbon
A chiral (or asymmetric) carbon atom is one which has four different groups attached to it.
What does a chiral carbon atom mean for the possible structures of the molecule
It’s possible to arrange the groups in two different ways around the carbon atom so that two different molecules are made
These molecules are called enantiomers or optical isomers
What are enantiomers
Enantiomers are mirror images of eachother
No matter which way you turn them, they can’t be superimposed
What does being optically active mean for a molecule
Optical isomers are optically active
They can rotate plane-polarised light
One enantiomer rotates it in a clockwise direction
The other rotates it the same amount but in an anticlockwise direction
Difference between normal light and plane polarised light
Normal light vibrates in all directions
Plane-polarised light only vibrates in one direction
How to identify the different enantiomers
Can be identified as D and L isomer
(don’t need to know which is which)
How do you normally find chiral compounds in nature
Chiral compounds are common in nature
Usually only 1 enantiomer can be found
E.g. all naturally occurring amino acids are L-amino acids and most sugars are D-isomers
When is an amine most reactive
When it has the maximum amount of R groups attached to the Nitrogen
They donate electron density towards the lone pair to make it more effective to act as a nucleophile
How to turn an ammonium salt back into an amine
React it with a base (NaOH) to reform the amine, a salt from the base (NaCl) and H2O
Name
What is a molecule that can be superimposed called
If a molecule can be superimposed on its mirror image, it’s achiral and it doesn’t have an optical isomer.
How does recrystallisation work
Solid is dissolved in minimum amount of warm solvent to make a saturated solution
Let it cool and solubility of product falls
It then forms crystals when it reaches a point when it can’t stay in solution
Process of recrystallisation
Very hot solvent is added to impure solid until it just dissolves
Produces saturated solution of impure product
Solution left to cool and crystals of product form
Impurities stay in solution as they are in small amounts so take longer to crystallise
Crystals then removed by reduced pressure filtration and washed in ice cold solvent
Then leave to dry to give crystals of pure product
How do you make a carbon chain longer during organic synthesis
Need reactants and reagents that have a nucleophilic or electrophilic carbon atom
Cyanide (CN-) has a negatively charged carbon atom which acts as a nucleophile
It reacts with carbon centres that have a slight positive charge to create a new carbon bond
This produces a nitrile
What specific reagents to use to increase the carbon chain
React a compound that contains a slightly positive carbon centre with a cyanide reagent:
KCN, NaCN, HCN
Mechanism for the reaction between a haloalkane and cyanide ion
Nucleophilic substitution
How to increase carbon chain using nucleophilic substitution
Relfux haloalkane with NaCN or KCN in ethanol to make it undergo nucleophilic substitution to form the nitrile
How to increase carbon chain using nucleophilic addition
Aldehydes and ketones contain a polar C=O
Mixing them with hydrogen cyanide (HCN) will allow the CN- with react with the positive carbon centre to form a hydroxynitrile
Mechanism for increase carbon chain length with nucleophilic addition
Why are nitrile groups useful in 2 step synthesis
Nitrile (or hydroxynitrile) are very reactive meaning they can be made into a new functional group
How to reduce a nitrile and hydroxynitrile to a primary amine
Can use LiAlH4 (strong reducing agent) then dilute acid
Na and ethanol
H2, Ni or Pt catalyst at high temperature and pressure (catalytic hydrogenation)
Equations for reducing nitrile to a primary amine using LiAlH4 or H2
Equation for reducing hydroxynitrile to a primary amine using LiAlH4
Why is catalytic hydrogenation used to reduce nitriles more than other methods
LiAlH4 and sodium are too expensive for industrial use
How to turn a nitrile or hydroxynitrile into a carboxylic acid
Refluxing with dilute HCl causes the nitrile group to be hydrolysed to form a carboxylic acid
Equation for hydrolysing nitrile to carboxylic acid
Equation for hydrolysing hydroxynitrile to carboxylic acid
Why is the solvent used in recrystallisation important
Recrystallisation will only work if the solid is very soluble in the hot solvent but nearly insoluble when the solvent is cold
If product isn’t soluble enough in the hot solvent then it won’t be able to be dissolved at all
If the product is too soluble in the cold solvent, most of it will stay in solution even after cooling
Means that when you filter, most of the product will be lost giving a low yield
What is filtering under reduced pressure used for
Used to separate solid product from any liquid impurities
This is because the reduced pressure caused suction through the funnel causing the liquid to pass quickly into the flask which leaves behind dry crystals of the product
How to carry out reduced pressure filtration
The reaction mixture is poured into a Büchner funnel with a piece of filter paper in it.
The Büchner funnel is on top of a sealed sidearm flask which is connected to a vacuum line, causing it to be under reduced pressure.
How does melting and boiling points use to determine purity
Most pure substances have a specific melting and boiling point.
If they’re impure, the melting points lowered and the boiling point is raised.
If they’re very impure, melting and boiling will occur across a wide range of temperatures.
How to accurately measure melting point
Put a small amount of the solid in a capillary tube and gently tap the tube to get the solid to fall to the bottom.
Place the tube in a beaker of oil with a very sensitive thermometer.
Slowly heat, with constant stirring until the solid just melts and read the temperature on the thermometer.
How to check the purity of a product after melting point has been obtained
Can compare the experimental melting point to a known melting point of the substance to determine its purity
If the melting points are similar then your sample is quite pure
If the value is much lower than the standard value then your sample has impurities
What amine is the most basic
Least: aromatic
Primary
Secondary
Most: tertiary
Tertiary have the most alkyl groups which donate electrons by inductive effect so there are more electrons present to readily donate and act as a nucleophile
