4.6 Amines Flashcards
Define an amine
- compound in which one or more of the hydrogen atoms in ammonia have been replaced by an organic functional group
Draw a primary amine
Draw a secondary amine
Draw a tertiary amine
Draw ammonium salt
Draw an amide
What is the indication for a secondary amine?
N
What is the indication for a tertiary amine?
N,N
What are the 2 methods of forming amines?
- halogenoalkanes using nucleophilic substitution
- reduction of a nitrile
Draw the formation of a primary amine using bromoethane
- NH3 as reagent
Draw nucleophilic substitution to form secondary amine from bromoethane
- primary amine as reagent
How do you form aromatic amines?
Reduction of nitrobenzene
Draw mechanism for reduction of nitrobenzene including reducing agents
- tin, conc HCl, NaOH
Why can’t nucleophilic substitution be done on chlorobenzene?
- Cl repels the lone pair
- C-Cl is a really strong bond because the delocalised electrons in the benzene ring repel the lone pair on the incoming nucleophile
Weakest to strongest bases of the amines
- aromatic
- ammonia
- primary
- tertiary
- secondary
Why can amines be described as bases?
- they have a lone pair
- by Bronsted-Lowry definition - they accept protons
Why are aromatic amines such weak bases?
- electron density pulled into the aromatic ring due to delocalised electrons
- lone pair on the nitrogen is less readily available to react and form a coordinate bond
Why are tertiary amines the second strongest base?
- alkyl groups crowd the nitrogen so its lone pair is not as available to bond
Why are secondary amines the strongest base?
- alkyl groups push electron density toward nitrogen, making the lone pair more available
—> positive inductive effect
Describe the trend in boiling points of primary amines
- as alkyl chain length increases, boiling temp increases
- more VdW need breaking therefore more energy is required
Describe the trend in boiling points of secondary amines
- boiling point of SA is lower than its corresponding PA
—> fewer hydrogen bonds can form due to there being only one hydrogen atom available on the nitrogen atom for bonding
—> weaker VdW, less H bonds, therefore lower boiling point
Boiling points of amines vs alkanes
- amine is higher than corresponding alkane
- NH bond enables hydrogen bonding and VdW whereas alkenes just have VdW
Boiling points of amines v alcohols
- amines have lower boiling point than their corresponding alcohol
- nitrogen is less electronegative than oxygen so the hydrogen bonds between amine molecules are weaker than those between alcohol molecules
Describe the trend in solubility in amines
- smaller amine chain makes it more soluble
- form hydrogen bonds between lone pairs in H2O and the hydrogen on amine
- tertiary amines less soluble as the nitrogen atom is overcrowded so less available to form a hydrogen bond
Draw 1,4-diaminobutane hydrogen bonding in water
How do you maximise the amount for primary amines less soluble formed from nucleophilic substitution?
- excess ammonia
How do you maximise the formation of quaternary salts?
- excess halogenoalkanes
Draw the reduction of nitrile including the reducing agents
- LiAlH4 dissolved in ether
Why can an amide act as a base?
It contains a nitrogen atom that has a lone pair of electrons and is a proton acceptor
Draw the functional groups of an amide and acid chloride
What are the 3 reactions of amines?
- ethanoylation
- nitric acid
- benzenediazonium
Draw the addition elimination reaction for ethanoyl chloride (ethanoylation)
- amines act as nucleophile due to the lone pair on the nitrogen atom
- attack the positive carbon in the carbonyl group in an acid chloride to form an amide
What reagent is used to produce an amide from an amine?
X-oyl chloride
(ie pent, eth, meth etc)
Draw the mechanism for the production of an amine and carboxylic acid from anhydrides
What is meant by a chromophore?
Part of the a molecule responsible for colour
Equation for the formation of nitrous acid
NaNO2 + HCl —> HNO2 + NaCl
What happens when nitrous acid reacts with aliphatic amines?
Forms an alcohol
—> R-NH2 + HNO2 —> R-OH + N2 + H2O
What happens when nitrous acid is reacted with aromatic amines?
Forms a solution containing benzenediazonium ions
Describe a test to differentiate between aliphatic and aromatic amines
- add nitrous acid below 10°C
- if N2 is seen, it is a primary aliphatic amine
- if no N2 is seen, it is an aromatic amine
What happens to a benzenediazonium ion above 10°C?
It decomposes to phenol and nitrogen
Draw mechanism for the coupling reaction of phenol and an aromatic amine
