Citral

Citral (CAS #5392-40-5) is a naturally occurring aroma chemical recognized for its strong, fresh citrus scent, making it a key ingredient in lemon-scented fragrances and flavorings. It is a colorless to pale yellow, oily liquid that occurs as a mixture of two geometric isomers: citral a (geranial, trans-citral) and citral b (neral, cis-citral), both contributing to its characteristic lemon aroma123.

Key Properties

• Chemical Formula: C₁₀H₁₆O

• Appearance: Colorless to light yellow liquid

• Odor: Intense, lemon-like, citrus aroma

• Boiling Point: 228–229°C

• Density: ~0.89 g/cm³ at 20–25°C

• Solubility: Practically insoluble in water; soluble in ethanol, ether, propylene glycol, and mineral oil13

• Stability: Sensitive to air and light; can oxidize and isomerize readily3

Natural Sources

Citral is a major component in the essential oils of many citrus fruits, including lemon, lime, orange, lemongrass (up to 85%), and Litsea cubeba (up to 75%)13. It is also present in verbena, white lemon, and citrus leaf oils.

Uses and Applications

• Fragrance: Citral is widely used in perfumery for creating citrus and lemon notes in various fragrance accords. It can be blended with D-limonene for a sweeter profile and is essential in formulating lemon, bergamot, and orange leaf scents2.

• Flavoring: Approved as a food additive, citral is used to flavor products such as soft drinks, candies, baked goods, chewing gum, and cold beverages. It imparts a fresh, fruity, and juicy citrus note to foods13.

• Aromatherapy: Its uplifting and refreshing qualities make it popular in aromatherapy for stress and anxiety relief.

• Antimicrobial Agent: Citral exhibits antimicrobial properties, making it useful in cleaning and disinfecting products, as well as in personal care items like soaps and lotions1.

• Insect Repellent: It is also known to repel insects and is used in natural insect repellent formulations.

• Chemical Intermediate: Citral serves as a key raw material for synthesizing ionones, methyl ionones, dihydrodamascone, vitamins A and E, and other aroma chemicals. It can be reduced to citronellol, nerol, and geraniol13.

Production and Synthesis

Citral can be sourced from natural essential oils or synthesized industrially. Common synthetic methods include:

• Dehydrogenation of Geraniol or Nerol: Using a copper catalyst in vapor phase, or from dehydrolinalool with vanadium catalysts2.

• Condensation Reactions: Starting from methyl heptenone, or by extracting from Litsea cubeba oil using sodium bicarbonate and sodium sulfite, followed by purification and distillation3.

Safety and Handling

• Toxicity: Generally recognized as safe (GRAS) for food use within regulated limits, but can cause skin sensitivity in some individuals.

• Storage: Store in a cool, dry place, away from light and heat to prevent oxidation and isomerization3.

Summary Table

Citral’s strong citrus aroma, versatility, and functional properties make it a cornerstone ingredient in the fragrance, flavor, and household product industries