Question

explain Haworth synthesis of naphthalene

Answer 1

Naphthalene is an organic compound with formula  C10H8. It is the simplest polycyclic aromatic hydrocarbon and a white crystalline solid with a characteristic odour that is detectable at concentrations as low as 0.08 ppm by mass.

As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings. It is best known as the main ingredient of traditional mothballs.

It can be synthesized by Haworth synthesis, the steps are as follows:

1. The Friedel craft acylation reaction of benzene with succinic anhydride gives 3 benzoylpropionic acid. 

2. Next is the Clemmenson’s reaction with  3-benzoylpropionic acid which gives 4-phenylebutanoic acid.

3. On heating this product in the presence of conc. sulfuric acid results in the formation of ring structure of α-tetralene by the ellimination of water molecule. 

4. The Clemmenson reaction of α-tetralene gives tetrahydronaphthalene.

5. Dehydrogenation of tetrahydronaphthalene in the presence of selenium yields naphthalene.