Source and Occurrence
Citral is a key component of lemongrass (Cymbopogon citratus) and lemon myrtle (Backhousia citriodora) essential oils.
It exists in two isomeric forms: geranial (trans-citral) and neral (cis-citral).
Isolation of Citral
Extraction
Steam Distillation: Similar to menthol, citral is extracted via steam distillation of lemongrass leaves.
Solvent Extraction: Alternatively, organic solvents like hexane or ethanol can be used to extract essential oils containing citral.
Separation
Post-distillation, the essential oil is separated from water.
Fractional Distillation: To isolate citral from other components based on boiling points.
Purification
Chromatography: Utilizing techniques like column chromatography on silica gel to separate citral from other terpenoids.
Recrystallization: Not typically applicable for citral as it is a liquid at room temperature, but distillation under reduced pressure can enhance purity.
Identification
Physical Properties
Appearance: Colorless liquid.
Boiling Point: ~230°C.
Odor: Strong lemon-like aroma.
Spectroscopic Techniques
IR Spectroscopy: Detects functional groups such as aldehyde (~1720 cm⁻¹) and C=C stretching (~1650 cm⁻¹).
¹H and ¹³C NMR Spectroscopy: Elucidate the molecular structure, confirming the presence of aldehyde and double bonds.
Mass Spectrometry: Molecular ion peak at m/z 152.
Chromatographic Techniques
GC: Essential for separating citral isomers and confirming purity via retention times.
HPLC: Used for quantitative analysis.
Analysis
Quantitative Analysis
GC-FID: Measures citral concentration in essential oils.
HPLC: Provides precise quantification in purified samples.
Quality Control
Assessing purity through spectral data and chromatographic profiles.
Ensuring absence of impurities or other isomers beyond acceptable limits.
Applications and Significance
Citral is widely used in the flavor and fragrance industry for its lemon scent.
It also possesses antimicrobial and anti-inflammatory properties, making it valuable in cosmetics and medicinal formulations.