Source and Occurrence
Quinine is obtained from the bark of the cinchona tree (Cinchona officinalis, Cinchona bark).
It is a bitter alkaloid with antimalarial properties.
Isolation of Quinine
Extraction
Bark Processing: The bark is dried and powdered.
Alkaloid Extraction: Mixed with an acidic aqueous solution (e.g., dilute HCl) to convert quinine into its water-soluble salt.
Purification
Liquid-Liquid Extraction: Basify the solution with NaOH to free the quinine base, which is then extracted into an organic solvent like ether or chloroform.
Crystallization: Quinine is crystallized from the organic phase by adding a non-solvent (e.g., ethanol).
Chromatography
Column Chromatography: Further purification using silica gel columns and appropriate solvent systems.
Identification
Physical Properties
Appearance: White crystalline solid.
Melting Point: Approximately 176-180°C.
Solubility: Soluble in alcohol, ether, and slightly soluble in water.
Spectroscopic Techniques
IR Spectroscopy: Identifies functional groups such as quinoline ring and hydroxyl groups.
NMR Spectroscopy:
¹H NMR: Characteristic signals from the quinoline moiety and ethyl side chain.
¹³C NMR: Confirms the quinoline ring structure.
Mass Spectrometry: Molecular ion peak at m/z 324 (free base).
Chromatographic Techniques
HPLC: For purity assessment and quantification.
TLC: Used during extraction and purification stages.
Analysis
Quantitative Analysis
HPLC with UV Detection: Standard method for quinine quantification, especially in pharmaceutical formulations.
Spectrophotometric Methods: Utilizing specific detection wavelengths.
Quality Control
Ensuring the absence of other cinchona alkaloids like quinidine.
Confirming structural integrity through spectroscopic data.
Applications and Significance
Quinine is historically significant as the first effective treatment for malaria.
It is also used in tonic water and serves as a precursor for synthesizing other antimalarial drugs.
Its bitter taste has led to widespread use in beverages and flavorings.