Chapter 16.SE, Problem 57AP

Interpretation Introduction

a)

Interpretation:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how 2-bromo-4-nitrotoluene can be synthesized is to be stated.

Concept introduction:

In aromatic electrophilic substitution reactions halogens and methyl group are ortho and para directing groups while the nitro group is a meta directing group. Hence to prepare 2-bromo-4-nitrotoluene, toluene has to be halogenated and the chlorotoluene obtained should be nitrated.

Electrophilic substitution of di and trisubstituted benzenes follows three simple rules. (i) If the directing influence of both the substituents reinforce each other, a single product results. (ii) If the directing influences of both the substituent groups oppose each other, the most powerful activating group among them has the dominant influence but usually a mixture of products results. (iii) In meta disubstituted compounds, further substitution in between the groups occurs only rarely, due to steric reasons.

To state:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how 2-bromo-4-nitrotoluene can be synthesized.

Interpretation Introduction

b)

Interpretation:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how 1,3,5-trinitrobenzene can be synthesized is to be stated.

Concept introduction:

In aromatic electrophilic substitution reactions the nitro group is a meta directing group. Nitration of benzene gives nitrobenzene. Further nitration of nitrobenzene will introduce nitro groups into the two meta positions to yield the trinitro compound.

To state:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how 1,3,5-trinitrobenzene can be synthesized.

Interpretation Introduction

c)

Interpretation:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how 2,4,6-tribromoaniline can be synthesized is to be stated.

Concept introduction:

In aromatic electrophilic substitution reactions, the amino group is an ortho and para directing group. Nitration of benzene gives nitrobenzene. Nitrobenzene can be reduced to aminobenzene (aniline). Aniline upon bromoination will yield 2,4,6-tribromoaniline.

To state:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how 2,4,6-tribromoaniline can be synthesized.

Interpretation Introduction

d)

Interpretation:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how m-fluorobenzoic acid can be synthesized is to be stated.

Concept introduction:

In aromatic electrophilic substitution reactions the carboxylic acid group is a meta directing group. Hence to prepare m- fluorobenzoic acid, benzene should be first converted into benzoicacid. Direct fluorination of aromatic rings is not possible as fluorine is too reactive and it is not possible to stop the reaction at the monofluorinated stage. Fluorination is normally carried out using F-TEDA-BF₄ which has a fluorine atom bonded to positively charged nitrogen.

To state:

Starting from benzene or toluene and assuming that the ortho and para isomers can be separated, how m-fluorobenzoic acid can be synthesized.