What Is Citral?
Citral is the name given to a mixture of a pair of isomers, the organic compounds neral and geranial. Its IUPAC nomenclature name is 3,7-dimethyl-2,6-octadienal, and it is also sometimes referred to by the alias lemonal.
Both isomers are monoterpene aldehydes with the molecular formula C10H16O and are cis-trans isomers: E is geranial and Z is neral. The CAS registration number of citral is 5392-40-5.
Uses of Citral
Citral has a lemon-like aroma, so it is used as an excipient in cosmetics and foods, as well as in various products such as perfumes, cosmetics, facial cleansers, body soaps, shampoos, detergents, and foods.
In natural products, it is a substance present in essential oils of lemongrass, lemon, mandarin, and various other fruits and spices. Because of its high volatility and strong aroma, it is used in top notes, which are the first to be perceived in fragrance formulations.
It is also used as a raw material for the production of other flavors and fragrances.
Citral is also a useful compound as a raw material for general organic synthesis. It is used as a raw material for synthesizing chemicals such as vitamin A and vitamin E
Properties of Citral
Citral is a mixture of geranial and neral. It has a molecular weight of 152.24, a melting point below -10°C, and a boiling point of 229°C. It is a colorless to pale yellow liquid at room temperature. It is susceptible to oxidation and gradually takes on a yellowish color upon exposure to air. It has a density of 0.893 g/mL
Citral is easily soluble in ethanol and ether, but insoluble in water. It has a characteristic aroma, of which geranial has a cool, strong lemon odor, while neral has a weak lemon odor and sweet taste.
Types of Citral
Citral is generally sold as a reagent product for research and development and as a raw material for fragrances. As a reagent product for research and development, it is available in various capacities, such as 1mg, 5mg, 5mL, 100mL, 500mL, 25g, 1kg, etc., depending on the manufacturer.
Reagent products may be treated as refrigerated reagents or as reagents that can be handled at room temperature.
Note that reagent products can only be used for research and development purposes, not for medical, clinical diagnostic, or food use in humans or animals.
Industrial products are sold by several companies, including fragrance and chemical manufacturers.
Sales are developed in a variety of packing sizes ranging from 1L bottles to ultra-large capacities such as 25L drums, 180kg drums, and 200L drums. The product offerings are tailored to factories and other manufacturing sites.
Other Information on Citral
1. Production and Synthesis of Citral
Citral is contained in various essential oils, so it can be produced by separation from essential oils. It can also be produced synthetically, sometimes using methyl heptenone as a raw material.
The following synthetic route is an example of synthesis:
- Condensation reaction of methyl heptenone with ethoxyacetylene magnesium bromide
- Catalytic partial hydrogenation (formation of enol ethers)
- Hydrolysis and dehydration with phosphoric acid
One other synthetic example is via the dehydrolinalool intermediate produced by the condensation reaction of acetylene with methyl heptenone. This intermediate is rearranged at 140-150°C in the presence of a silicon sulfone catalyst in an inert solvent to give citral.