Amines Flashcards
What is the definition of a primary amine
Only one carbon directly attached to the nitrogen atom and therefore had for NH2 group
What is the definition of a secondary amine
Two carbon atoms directly attached to the nitrogen atom
Definition of tertiary amine
Three carbon atoms directly attached to the nitrogen atom
Describe the process of nomenclature of amines
- Prefix = alkyl or aryl group
Suffix = -amine - More complex then amino- is the prefix
- If another functional group then use prefix of amino-
Describe the physical properties of amines (4)
- Lone pair of e on N atom
2 H bonding between amines - Lower bp than alcohols and carboxylic acids - N less electronegative than O so weaker H bonding
- Short = soluble in water - H bonding
What are the two methods of preparing a primary aliphatic amine
- Reduction of nitriles
2. Substitution of NH3 with halogenoalkane
Describe how to reduce a nitrile
Reflux nitrile with lithal (dissolved in dry ether)
Describe how NH3 is reacted with Halogenoalkanes
Halogenoalkane heated with ethanolic solution of NH3 in sealed Metal, tube
Describe how to prepare phenylamine
- Nitrobenzene refluxed with reducing agent (tin and conc HCl)
- This gives phenylammonium ion
- Phenylamine liberated by addition of NaOH
What causes an amine to have a greater base strength
If the lone pair of electrons on the N are more available
What is the order of base strength for amines (from weakest to strongest)
Phenylamine ➡️ ammonia ➡️ primary amine ➡️ secondary amine ➡️ tertiary amine
Why do aliphatic amines have a greater base strength than ammonia
- Alkyl groups push e away
- small amount of extra negative charge on N
- more attractive to H+
Why is phenylamine a very weak base
Lone pair of N touch ring
- delocalisation has to be disrupted which costs energy
- lone pair no longer fully available to combine with H+ so lack of charge
What does the reaction of amines with ethanoyl chloride produce
N-substituted amide
HCl
How do you identify an unknown amine
- React amine with ethanoyl chloride
- Solid amide derivative dissolved in hot solvent, filtered, cooled and crystallises
- Suction filtered, wash w cold solvent, dry
- Heat slowly - compare melting point with data
Why is the reaction of phenylamine with nitrous acid performed under 5degrees
Above 5 and the benzene diazonium ion will decompose
What is the definition of coupling
Reaction in which 2 benzene rings are linked together through an azo group
What colour is the azo dye produced when benzene diazonium chloride reacts with phenol/phenylamine
Yellow precipitate/solid
Why are azo compounds coloured?
1️⃣ They have an extensive delocalised electron system
2️⃣ This brings the electronic energy levels closer together
3️⃣ This promotes electrons and light is absorbed in the visibility region of the spectrum
- the colour observed is the complementary colour of the colour observed
Why would compounds appear white or colourless?
- the energy levels are far apart
- electrons need to absorb a lot of energy to jump to the next energy level
What are the two uses of Azo-compounds
Dyestuffs
Acid-base indicators
Why are azo compounds used as dyestuffs
- They are brightly coloured - due to the absorption of a particular wavelength of light by the azo-group
Why are azo compounds used as acid-base indicators
- they have an extended pi delocalised system
- dist between electronic energy levels becomes smaller
- less energy required to promote an electron to a higher energy level
- wavelength of light that is absorbed becomes longer
- wavelength absorbed corresponds to the visible region
