Diphenyl amine when treated with sulphur undergoes fusion reaction in the presence of iodine to give phenothiazine, a tricyclic compound with rapid evolution of hydrogen sulphide.
In a round bottom flask fitted with reflux condenser, place 16.8 g of diphenylamine, 6.4 g of sulphur and 300 mg of iodine. Reflux the mixture on an oil bath at 190-200°C for 30-40 minutes with the rapid evolution of hydrogen sulphide. By lowering the temperature, a few degrees the reaction can be slackened. Cool and grind the residue mass, in which 5 ml of ethanol and pinch of animal charcoal is added and heat it until solid mass dissolves. Filter the solution while hot and cool in ice bath. The residue consists of almost pure phenothiazine. It can be recrystallised from alcohol. The melting point of the yellow crystals of phenothiazine is 184-185°C.
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The Phenothiazine was synthesized from Diphenyl amine. The practical yield and percentage yield was found to be …… and ……. respectively. The melting point was found to be ….. °C.