Reaction of arenes - nitration

Question 1

What is nitration?

Answer 1

the substitution of a NO2 group for one of the hydrogen atoms

Question 2

How is NO2+ produced?

Answer 2

in the reaction mixture of concentrated nitric acid and concentrated sulfuric acids

H₂SO₄ + HNO₃ → H₂NO₃+ + HSO₄^-

sulfuric acid is a stronger than acid than nitric acid and donates a proten to HNO₃

H2NO3+ then loses a molecule of water to give NO2+, which is called the nitronium ion or nitryl cation

H₂NO₃⁺ → NO₂⁺ + H₂O

Question 3

What is the general equation for the generation of NO2+?

Answer 3

H₂SO₄ + NHO₃ → NO₂⁺ + HSO₄^- + H₂O

Question 4

Draw the mechanism for the electrophillic substition of the nitronium ion

Answer 4

Question 5

How does sulfurice acid act as a catalyst?

Answer 5

the H⁺ then reactis with HSO₄^- to regenerate H₂SO₄, making it a catalyst

Question 6

what are the uses of nitrated arenes?

Answer 6

nitration is an important step in the production of explosives like TNT

nitration is the first step in producing aromatic amines, and these in turn are used to make industrial dyes

Question 7

How can arenes be further substituted? depending on the atoms on a benzene ring

Answer 7

1. may release electrons onto the benzene ring and therefore make it more susceptible to further electrophillic susbstitution reaction
2. or will withdraw electrons from the ring making it less susceptible
3. it will direct further substition to a particular position on the ring. Electron-releasing groups direact further susbsitution to the 2, 4 and, 6 position. Electron-withdrawing groups direct further substituion to the 3 and 5 positions

Question 8

What is the Friedal-Crafts acylation reaction?

Answer 8

use aluminium chloride as a catalyst

the mechanism for acylation is a substituion, with RCO substituing for a hydrogen on the aromatic ring

Question 9

How is the RCO group provided?

Answer 9

acyl chlorides provide the RCO group

they react with AlCl₃ to form AlCl₄ and RCO⁺

RCOCl + AlCl₃ → RCO⁺ + AlCl₄^-

Question 10

How does the reaction (providing the RCO group) take place?

Answer 10

the aluminium atom in the aluminium chloride has only six electrons in its outer main level and readily accepts a lone pair from the chlorine atom of RCOCl

Question 11

How does aluminium chloride act as a catalyst? what is the reaction for this?

Answer 11

it is reformed by the reaction of the AlCl₄^- ion with H⁺ from the benzene ring

AlCl₄^- + H₊ → AlCl³ + HCl

Question 12

Draw the mechanism for the reaction of alcylation

Answer 12

Question 13

How does H2SO4 act as catalyst?

Answer 13

HSO4- accepts a hydrogen released from benzene ring to reform H2O4