Arenes Organic RXNs

Question 1

phenol to 2-bromophenol

Answer 1

(1) Br2 (l), CCl4, rtp (Electrophilic Substitution)

Question 1

benzene to benzoic acid

Answer 1

(1) CH3Cl, anhydrous FeCl3/AlCl3, rtp (Electrophilic sub)

(2) H2SO4 (aq), KMnO4 (aq), heat under reflux (Side Chain Oxidation)

Question 2

benzene to phenylamine

Answer 2

(1) conc. HNO3, conc. H2SO4, 55C (Electrophilic Substitution)

(2) Sn. Conc. HCl + NaOH (aq), rtp (Reduction)

Question 3

benzene to chlorobenzene

Answer 3

(1) Cl2 (g), anhydrous FeCl3/AlCl3 rtp (Electrophilic Substitution)

Question 4

chlorobenzene to 1-chloro-4-nitrobenzene
+
why do we have to heat at more than 55C?

Answer 4

(1) conc. HNO3, conc. H2SO4, heat at >55C (Electrophilic Substitution)

Harsher conditions (>55C) are required as Cl (or -X) is a ring-deactivating group. Since Cl (or -X) is more electronegative than the carbon it is attached to via sigma bonds, it will attract the electron pair towards itself, reducing the overall electron density of the benzene ring. This means that the benzene ring is now less available for electrophilic attacks and substitution reactions since there are less electrons available for these electrophiles (electron negative). Furthermore, since Cl is in period 3, the p orbital are more diffuse leading to a less effective sideways overlap with the p orbitals of the benzene ring. As such, the inductive effect is stronger than the resonance effect and -Cl is electron-withdrawing. As a result, harsher conditions like a higher temperature are required to initiate the reactions successfully.

Question 5

benzene to methylbenzene

Answer 5

(1) CH3Cl, anhydrous FeCl3/AlCl3, rtp (Electrophilic Substitution)

Question 6

phenylamine to 2,4,6-tribromophenylamine (state colour of ppt)

Answer 6

(1) Br2 (aq) (Electrophilic Substitution)
(White ppt)

Question 7

benzene to benzylchloride

Answer 7

(1) Cl2 (g), anhydrous FeCl3/AlCl3, rtp (Electrophilic Substitution)

Question 8

benzene to benzaldehyde

Answer 8

(1) RCOCl, anhydrous FeCl3/AlCl3, rtp (Electrophilic Substitution)

Question 9

phenol to 2,4,6-trinitrophenol (state colour of ppt)
+
How to test for presence of Phenol

Answer 9

(1) Conc. HNO3, rtp (Electrophilic Substitution) (yellow ppt)
+
Neutral FeCl3 solution (yellow solution) : Violet ppt formed