Question

Safrole, a substance isolated from the oil of sassafras, is used as a perfumery agent. Propose a synthesis of safrole from catechol (1,2-benzenediol).

Short answer

Whencatechol, i.e. benzene with two hydroxyl groups in first and second position, istreated with sodium hydride, each of the hydrogen atoms in hydroxyl groups are lost and forms an ion with sodium. So two molecules of hydrogen is released.

Step-by-step solution

Treating catechol with sodium hydride

Whencatechol, i.e. benzene with two hydroxyl groups in first and second position, istreated with sodium hydride, each of the hydrogen atoms in hydroxyl groups are lost and forms an ion with sodium. So two molecules of hydrogen is released.

Step 2: Treatment with dibromomethane to form cyclisation

The next step is to treat with dibromomethane which cyclizes the ion obtained earlier. Thus both oxygen atoms in$C_1$ and$C_2$ forms a cyclic compound with the methyl group of dibromomethane. The products formed thereby are 1, 3 –benzodioxole and two moles of sodium bromide.

Friedel Craft’s reaction

1,3 – benzodioxole is further undergone Friedel Crafts reaction using 3-chloropropene and anhydrous aluminium chloride. This adds the allyl group at $C_5$and thus forms the safrole compound. The whole mechanism is shown below: