Quinine

Properties of quinine are:

1) It crystallises with three moles of water and melts at 177°C under anhydrous conditions.

2) It is laevo-rotatory and is bitter in taste.

3) Its sulphate or dihydrochloride salt is used as the most effective anti-malarial agent for many years.

4) Quinine and cinchonine have been used in the resolution of racemic mixtures via the formation of diastereoisomeric salts.

Quinine can be identified by the following tests:

1) Thalleioquin Test:

A small amount of quinine is dissolved in dilute sulphuric acid and 1 -2ml of water. To the resulting mixture, 2 -3 drops of bromine water are added and shaken. A drop of strong ammonia is added to the mixture which produces an emerald green colour.

2) Erythroquinine Test:

A quinine solution in dilute acetic acid is added with 1-2 drops of bromine water and a drop of 10% solution of potassium ferricyanide. A drop of strong ammonia solution is added to the mixture which produces a red colour.

3) Quinine gives a strong blue fluorescence in extremely dilute solutions of sulphuric, acetic, phosphoric or tartaric acids.

4) On slightly moistening small quantity of quinine with glacial acetic acid and heating in an ignition tube, blood-red drops condense on the sides of the tube.

Isolation Method

• 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 few hours.

• The moistened material is packed in Soxhlet apparatus and extracted with benzene.

• 5 % sulphuric acid is added in benzene extract and mixed well.

• The two layers are formed which are separated cautiously.

• The benzene layer is discarded and sodium hydroxide is added in the aqueous layer to maintain the pH 6.5.

• Then it is allowed to cool and quinine sulphate 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 colouring matter.

• The obtained quinine sulphate 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 alkaloid is spotted in Silica gel-G plates

• 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.

Analysis

• Reagents Dilute sulphuric acid (0.05M) prepared by adding 3.0ml concentrated sulphuric acid to 100ml water, and diluting up to 1000ml with distilled water.

Standard Solution of Quinine

• Accurately weighed 0.1gm of quinine is dissolved in 1L 0.05M sulphuric acid in a graduated flask.

• 10ml of this solution is diluted to 1000ml with 0.05M sulphuric acid so th at the resulting solution contains 0.00100mg/ml quinine.

• Using a calibrated burette, 10.0, 17.0, 24.0, 31.0, 38.0, 45.0, 52.0 and 62.0ml of the above dilute standard solution is run into separate 100ml graduated flasks and each solution is diluted up to the mark with 0.05M sulphuric acid.

Procedure

• The fluorescence of each of the above solutions is measured at 445nm, using 62ml of dilute quinine solution as a standard for the fluorimeter.

• LF2 or an equivalent primary filter ( ex = 350nm) and gelatin are used as the secondary filters in a simple fluorimeter.

• Test solutions containing 0.00025 and 0.00045mg/ml quinine are prepared.

• Their concentrations are determined by measuring the fluorescence on the instrument and with the calibration curve.