3.11 - Amines Flashcards
How do you name amines?
-amine
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 degrees due to lne pair on N
What kinds of intermolecular forces do they have and 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 nenzene 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 nucleophilles?
When they bond with an electron-deficient C atom - donate a lone pair from N
What is the product from the basic action of an amine with water?
RNH3+ - ammonium ion, which forms a salt with an anion.
Is an ammonium ion soluble in salt? Why?
Yes as it is ionic so is attracted to the polar bonds in H20.
How could you regenerate the soluble amine from the ammonium salt?
Add a strong base (NaOH) -> removes H+ ions drom 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
What does positive/negative inductive effect mean?
Positive inductive effect = donate electrons, increase density around N
Negative means remove eletrons, decrease density around N
What effect do alkyl groups have on electron density and base strength?
Positive inductive effect - increase electron density aroun 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° amines never good bases?
They are insoluble in water
Place these in order of base strength ( weakest to strongest):
- NH3
- 1° amine
- 2° amine
- Phenylamine
2° amine
1° amine
NH3
phenylamine
How can primary amines then from 2°, 3° amines and 4° ammonium ions?
Multiple substitutions; primary amine is a nucleophile that attacks the original haloalkane etc
What are the problems with this method?
Not efficient as low yield of 1° 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 conditons 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?
Reduction using either Nickel or Hydrogen catalyst
Why is this a purer method of a synthesising amines?
Only the pimary 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 to phenylamine
C6H5NO2 + 6[H] –> C6H5NH2 + 2H20
What mechanism is used to form amides from acyl chlorides and amines?
Nucleophilic addition / elimination
In which industries / products are amines used?
Dyes, nylon, drugs, synthesis of new molecules
What are cationic surfactants used in fabric/ hairconditioners)?
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 conditioners?
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 surfacants sit when placed in water?
Charged end in the water, non-polar end sticking out of the water/ at the surface.
