Reactions of aromatics Flashcards
Why does benzene attract electrophiles?
The benzene ring is a region of high electron density
What is an electrophile?
Electron pair acceptor
What type of reaction does benzene undergo?
Electrophillic substitution
Why does benzene undergo electrophilic substitution and not electrophilic addition reactions?
They are stable and electrophile addition would destroy the delocalised ring of electrons
What is the first stage of the electrophilic substitution reaction?
The electron dense region at the centre of the benzene ring attracts an electrophile
What is the second stage of the electrophilic substitution reaction?
The electrophile steals a pair of electrons from the centre of the benzene ring and forms a bond with one of the carbons
What is the third stage of the electrophilic substitution reaction?
This partially breaks the delocalised electron ring and gives the molecule a positive charge
What is the 4th stage of the electrophilic substitution reaction?
To regain the stability of the benzene ring, the carbon which is now bound to the electrophile, loses a hydrogen
What is being substituted in an electrophilic substitution reaction?
H+ for the electrophile
What does a nitration reaction form?
Nitrobenzene
What needs to react together in order to form nitrobenzene?
conc. sulfuric acid and conc. nitric acid
what is important to remember about the sulfuric acid and nitric acid?
They are CONCENTRATED
you wont get the mark if you forget this
What is the equation for the reaction between concentrated nitric acid and concentrated sulfuric acid?
HNO₃ + H₂SO₄ -> HSO₄⁻ + NO₂⁺ + H₂O
In a nitration reaction, what does the sulfuric acid act as?
Catalyst
In a nitration reaction, what is the electrophile?
The nitronium ion formed
NO₂⁺
In a nitration reaction, what do you need to make sure is maintained? Why?
The temperature below 55 degrees Celsius
This makes sure only one NO₂ is added
Any higher and more than one will be added
What are uses of the nitration reaction?
Form aromatic amines
Dyes
Pharmaceuticals
TNT
What does the Friedel crafts acylation add to the benzene ring?
Acyl group
What is an acyl group?
-C(=O)-R
What are the products of a Friedel crafts reaction?
HCl
Phenylketone
In a Friedel crafts acylation reaction, how do the reactants need to be heated?
Under reflux in a non-aqueous solvent
What is a halogen carrier?
Catalyst which makes the electrophiles stronger
What is the halogen carrier involved in the Friedel crafts reaction?
AlCl₃
What is the equation for the formation of the electrophile in the Friedel crafts reaction?
R-C(=O)-Cl + AlCl₃ -> R-C+=O + AlCl₄⁻
In the Friedel crafts reaction, how does the catalyst reform?
the AlCl₄⁻ is attracted to the positively charged ring and one chlorine breaks off and joins with one of the hydrogens to create HCl
