Synthesis of 1,2,3,5- tetrabromobenzene from Benzene
The chemical synthesis of 1,2,3,5,- tetrabromobenzene from benzene is a multistep synthesis and consists of 5 steps;
1. Formation of Nitrobenzene
2. Formation of Aniline
3. Formation of 2,4,6- tribromoaniline
4. Formation of diazonium salt
5. Formation of 1,2,3,5- tetrabromobenzene
Scheme and mechanism of each step are given below;
Scheme:
 |
| synthesis of 1,2,3,5-tetrabromobenzene |
Mechanisms:
Mechanism of each step in synthesis of tetrabromobenzene is given below;
Step 1; Formation of Nitrobenzene (Nitration)
This is simple mechanism of electrophilic substitution on benzene through nitronium ion.
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| nitration of benzene to form nitrobenzene |
Step 2; Formation of Aniline (Reduction)
Reduction will take place in the presence of tin and hydrochloric acid. Most probable mechanism is given below.
KEY TO REMEMBER MECHANISM;
Tin will react three times for complete reduction in following way;
l First attack on nitro group
l Second attack on nitroso group
l Third attack after formation of hydroxylamine
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| reduction with tin and HCl |
Step 3; Formation of Tribromoaniline (Bromination)
Bromination of aniline will give tribromo product in the form of 2,4,6-tribromoaniline.
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| bromination of aniline |
Step 4; Formation of Diazonium salt (Diazotization)
Mechanism of formation of diazonium salt of tribromobenzene is given below;
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| formation of diazonium salt (diazotization) |
Step 5; Formation of Tetrabromobenzene (Sandemeyer Reaction)
This is just a replacement reaction of diazonium group by -Br I.e., sandemeyer reaction.
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| sandemeyer reaction |
These are the most commonly used steps in chemical synthesis of any compound. So, this is a commonly used way for the synthesis of tetrabromobenzene in chemical synthesis.
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