Amines

Question 1

What is the definition of a primary amine

Answer 1

Only one carbon directly attached to the nitrogen atom and therefore had for NH2 group

Question 2

What is the definition of a secondary amine

Answer 2

Two carbon atoms directly attached to the nitrogen atom

Question 3

Definition of tertiary amine

Answer 3

Three carbon atoms directly attached to the nitrogen atom

Question 4

Describe the process of nomenclature of amines

Answer 4

1. Prefix = alkyl or aryl group
   Suffix = -amine
2. More complex then amino- is the prefix
3. If another functional group then use prefix of amino-

Question 5

Describe the physical properties of amines (4)

Answer 5

1. Lone pair of e on N atom
   2 H bonding between amines
2. Lower bp than alcohols and carboxylic acids - N less electronegative than O so weaker H bonding
3. Short = soluble in water - H bonding

Question 6

What are the two methods of preparing a primary aliphatic amine

Answer 6

1. Reduction of nitriles

2. Substitution of NH3 with halogenoalkane

Question 7

Describe how to reduce a nitrile

Answer 7

Reflux nitrile with lithal (dissolved in dry ether)

Question 8

Describe how NH3 is reacted with Halogenoalkanes

Answer 8

Halogenoalkane heated with ethanolic solution of NH3 in sealed Metal, tube

Question 9

Describe how to prepare phenylamine

Answer 9

1. Nitrobenzene refluxed with reducing agent (tin and conc HCl)
2. This gives phenylammonium ion
3. Phenylamine liberated by addition of NaOH

Question 10

What causes an amine to have a greater base strength

Answer 10

If the lone pair of electrons on the N are more available

Question 11

What is the order of base strength for amines (from weakest to strongest)

Answer 11

Phenylamine ➡️ ammonia ➡️ primary amine ➡️ secondary amine ➡️ tertiary amine

Question 12

Why do aliphatic amines have a greater base strength than ammonia

Answer 12

• Alkyl groups push e away
• small amount of extra negative charge on N
• more attractive to H+

Question 13

Why is phenylamine a very weak base

Answer 13

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

Question 14

What does the reaction of amines with ethanoyl chloride produce

Answer 14

N-substituted amide

HCl

Question 15

How do you identify an unknown amine

Answer 15

1. React amine with ethanoyl chloride
2. Solid amide derivative dissolved in hot solvent, filtered, cooled and crystallises
3. Suction filtered, wash w cold solvent, dry
4. Heat slowly - compare melting point with data

Question 16

Why is the reaction of phenylamine with nitrous acid performed under 5degrees

Answer 16

Above 5 and the benzene diazonium ion will decompose

Question 17

What is the definition of coupling

Answer 17

Reaction in which 2 benzene rings are linked together through an azo group

Question 18

What colour is the azo dye produced when benzene diazonium chloride reacts with phenol/phenylamine

Answer 18

Yellow precipitate/solid

Question 19

Why are azo compounds coloured?

Answer 19

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

Question 20

Why would compounds appear white or colourless?

Answer 20

• the energy levels are far apart

- electrons need to absorb a lot of energy to jump to the next energy level

Question 21

What are the two uses of Azo-compounds

Answer 21

Dyestuffs

Acid-base indicators

Question 22

Why are azo compounds used as dyestuffs

Answer 22

• They are brightly coloured - due to the absorption of a particular wavelength of light by the azo-group

Question 23

Why are azo compounds used as acid-base indicators

Answer 23

• 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