3.11 Amines Flashcards
Draw the structures of primary, secondary and tertiary amines and a quaternary ammonium ion
How do you name amines?
-amine or amino-
Why are amines so reactive?
The lone pair of electrons on the nitrogen- due to polar N-H bond
What shape are amines around the N? Bond angle?
Trigonal pyramidal, 107 degree due to lone pair on N
What kind of intermolecular forces do they have? Why?
Hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom
Do amines have intermolecular forces which are stronger than or weaker than alcohols? Why?
Weaker, as N has a lower electronegativity than O —> weaker hydrogen bonding
What state are amines at 298K?
Short chains are gases, longer chains are volatile liquids
What do they smell of? Why?
Fishy smell - rotting fish/flesh releases di- and triamines
Which primary amines are soluble in water/alcohols? Why?
Up to 4 carbon atoms, as they can hydrogen bond to water molecules. After this, non-polarity of hydrocarbon chain makes them insoluble
What kind of solvents are most other amines soluble in?
Less or non-polar solvents
Solubility of phenylamine? Why?
Not very soluble, due to the non-polarity of the benzene ring - C6H5 cannot form hydrogen bonds
How can/when do amines act as bases?
When they bond with a H+ ion
How can/ when do amines act as nucleophiles?
When they bond with an electron deficient C atom (donate lone pair from N)
Draw a mechanism for the basic action of an amine with water
Slide 30
What is the product from the basic action of an amine with water?
RNH3 + - ammonium ion, which forms a salt with an anion
Is the product (ammonium ion) soluble in water? Why?
Yes, as it is ionic so is attracted to the polar bonds in H2O
How could you regenerate the soluble amine from the ammonium salt?
Add a strong base (NaOH) —> removes H+ ions from ammonium ion
In order to be the strongest base, what must a particular amine have (out of a set of amines)?
Greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)
What does positive/negative inductive effect mean?
Positive inductive effect = donate electrons, increase density around N
Negative means remove electrons, decrease density around N
What effect do alkyl groups have (on electron density and base strength)
Positive inductive effect - increase electron density around N —> stronger base
What effect do aryl groups have (on electron density and base strength)?
Negative inductive effect - decrease electron density around N —> weaker base
Why are 3^0 amines never good bases
They are insoluble in water
Place these in order of base strength (in general): NH3, 1^0 amine, 2 ^0 amine, phenylamine
2 ^0 amine > 1 ^0 amine > NH3 > phenylamine
Draw a mechanism for the nucleophilic substitution of NH3 with RCH2Br to form primary amines
Slide 50
How can primary amines then form 2 ^0,3 ^0 amines and 4 ^0 ammonium ions?
Multiple substitution; primary amine is a nucleophile that attacks the original haloalkane
What are the problems with this method
Not efficient as low yield of 1^0 amine due to multiple substitutions
How would you maximise the yield of the primary amine?
Use excess ammonia
What type of mechanism is the reaction of a haloalkane with a cyanide ion?
Nucleophilic substitution
What conditions does this reaction require? What is the product formed?
Ethanol as a solvent
A nitrile is formed
How do you get from a nitrile to a primary amine? (Name of reaction type and reagents/catalysts)
Reduction using nickel / hydrogen catalyst
Why is this a purer method of synthesising amines?
Only the primary amine can be formed
What conditions are needed to form nitrobenzene from benzene
Concentrated H2SO4 and HNO3 to form the NO2+ ion for electrophilic attack
How do you form an ammonium chloride salt from nitrobenzene? What conditions are needed?
Reduce the nitrile using Tin / HCl —> forms an ammonium salt with Cl- ions
Room temperature
Equation for the reaction of nitrobenzene —> phenylamine?
C6H5NO2 + 6[H] —> C6H5NH2 + 2H2O
What mechanism is used for forming amides from acyl chlorides and amines?
Nucleophilic additon/elimination
Draw a mechanism for the reaction of ethanoyl chloride with ethanamine
Slide 74
In which industries/products are amines used?
Dyes, nylon, drugs, synthesis of new molecules
What are cationic surfactants (used in fabric/hair conditioners)?
Quaternary ammonium salts, with a cation that is charged at one end (N+) and non polar at the other
How do cationic surfactants work in fabric/hair conditioner?
Negative charges on the surface of the fabric/hair are attracted to the cation, removing them from the surface; prevents build-up of static electricity and keeps hair flat and fabric smooth
How do cationic surfactants sit when placed in water?
Charged end in the water, non polar end sticking out of the water/at the surface
