Isolation of Quinine

Isolation of Quinine: Quinine is an alkaloid obtained from the dried stem bark and roots of Cinchona calisaya Wedd, Cinchona ledgeriana Moens, Cinchona officinalis Linn, and Cinchona succirubra Pavon or hybrids of these species belongs to the family Rubiaceae. Quinine is an optically laevorotatory compound whereas quinidine is a dextrorotatory isomer.

Fig.1: Quinine

The powdered bark of Cinchona is mixed with calcium hydroxide or calcium oxide and enough quantity of sodium hydroxide (5%) solution. Then the pasty material is allowed to stand for a few hours. The moistened material is packed in the Soxhlet apparatus and extracted with benzene. 5 percent sulphuric acid is added to benzene extract and mixed well. The two layers are formed which are separated cautiously. The benzene layer is discarded and sodium hydroxide is added to the aqueous layer to maintain the pH of 6.5. Then it is allowed to cool and quinine sulfate precipitate is formed. The precipitate is filtered, separated, and recrystallized from hot water. This process will free the salts from cinchonine and cinchonidine. The activated charcoal treatment will remove the coloring matter. The obtained quinine sulfate is dissolved in dilute sulphuric acid and made alkaline with ammonia. This process will precipitate the quinine and formed crystals are washed and dried at 45-55°C.

Melting point: 177°C.

Thin-layer chromatography of Quinine

The methanolic solution of the alkaloid is spotted in Silica gel-G plates and eluted in solvent systems chloroform: diethylamine (9:1) and chloroform: acetone: diethylamine (5:4:1). The plates are dried and sprayed with Dragendorff reagent. The Rf value of quinine is 0.17 in both solvent systems.

Identification Test of Quinine

Thalleioquin test: Dilute sulphuric acid (one drop) and water (1 ml) is added to the sample solution. Then add bromine water drop by drop till the solution acquires permanent yellow colour and add 1 ml dilute ammonia solution till emerald green colour develops.

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