Lilial is an aromatic aldehyde with the formula C₁₄H₂₀O and a molecular weight of 204.31 g/mol. Its IUPAC name is 3-(4-tert-butylphenyl)-2-methylpropanal. Lilial is a trade name for lily aldehyde and is also known as lysmeral or lilestralis. Its other names include butylphenyl methylpropional, BMHCA and p-BMHCA. It is a clear viscous liquid with a density of 0.94 g/cm³ and a melting point of -20 °C. Like most aldehydes, lilial tends to oxidize on storage. Further chemical names are 4-tert-butyl-α-methylhydrocinnamaldehyde and 2-(4-tert-butylbenzyl)propionaldehyde. The structural formula is written (CH₃)₃CC₆H₄CH₂CH(CH₃)CHO.
The CAS number 80-54-6 covers the racemic mixture; the (2R) form is 75166-31-3 and the (2S) form is 75166-30-2. The EC number is 201-289-8. Related aldehydes named alongside it are bourgeonal, isobutyraldehyde, hexyl cinnamaldehyde and 2-methylundecanal.
Further names are para-tert-bucinal and pt-bucinal, and it also appears as benzenepropanal, 4-(1,1-dimethylethyl)-alpha-methyl-. Its PubChem compound number is 228987.
Physical Properties and Storage
Its Kovats retention index lies between 1500 and 1549. A commercial grade has an acid value of at most 2.00 (KOH/g). Suppliers advise keeping it in a cool, dry place in tightly sealed containers, protected from heat and light and under nitrogen, and they give a shelf life of 24 months or longer when it is stored properly.
Its solubility in water is low, 0.045 g/L at 20 °C. It dissolves in alcohol and paraffin oil, and it is stable in detergent and soap. Its estimated vapor pressure is 0.005 mmHg at 25 °C, and it boils at 126 to 127 °C at 6 mmHg. Commercial assays run from 93% to 100%.
Chemistry
Lilial is commonly produced and sold as a racemic mixture, and testing has indicated that the different enantiomers of the compound do not contribute equally to its odor. It is also used as an intermediate in the synthesis of agrochemicals such as fenpropimorph and fenpropidin. It is also reported to have mosquito-repellent effects.
Enantiomers
The molecule has one chiral center, so it exists as two forms, (R)-lilial and (S)-lilial. Making and isolating the pure forms is difficult, because lilial is an α-chiral aldehyde, with the asymmetric carbon right next to the carbonyl group. The pure enantiomers would racemize easily after isolation through keto-enol tautomerism.
Purity and Stabilisation
The commercial material is a colourless to pale yellow liquid sold at a purity of at least 97.5% by weight, and one high-purity grade is specified above 99.0%. Air oxidation of lilial gives lysmerylic acid, 2-(4-tert-butylbenzyl)propionic acid. Alpha-tocopherol is added as a stabilizer directly after production, so only low concentrations of this acid are found in the product.
Safety and Regulation
The toxicity of Lilial is attributed to its degradation product tert-butyl benzoic acid. It can sometimes act as an allergen and may cause contact dermatitis in susceptible individuals. Its labelling was regulated under Annex III entry 83, which required it to be listed when its concentration exceeded 0.001% in leave-on products and 0.01% in rinse-off products. Lilial has been largely banned after being found to be harmful to fertility.
It has been identified as CMR of category 1B and is presumed to be toxic for reproduction based on animal studies. Regulation (EU) 2021/1902 added Lilial to Annex II of the EU cosmetics regulation. As a result, Lilial can no longer be used in cosmetics as of March 2022. Cosmetics that contain it cannot be placed on the EU market and must be removed from shelves if already on the market.
Commission Regulation (EU) 2021/1902, dated 29 October 2021, is also called the fourth European CMR or Omnibus IV regulation, and it lists Lilial as entry 1666 of Annex II. The Scientific Committee on Consumer Safety also expressed concern about higher exposure of users through non-cosmetic products.
Responsible persons, generally manufacturers or importers, may no longer supply products containing Lilial to their distribution partners. Distributors may not supply such products for distribution, consumption or use, whether for payment or free of charge. A distributor with reason to believe that a product does not comply must take the necessary measures itself.
Before the ban, the cosmetics rules regulated Lilial only for its allergenic properties. This regulation adds 23 ingredients to the annexes of the cosmetics regulation and applies from 1 March 2022. The ban rests on Article 14(1)(b) of the cosmetics regulation. Companies that use a Candidate List substance in their products must notify ECHA through the SCIP database.
The uses named there are cleaning agents, cosmetics, scented articles, polishes and wax blends. Producers and importers of articles containing a Candidate List substance have six months from publication to notify ECHA if it is present above one tonne per producer or importer per year and above 0.1% weight by weight. Suppliers of articles above that concentration must give their customers enough information for safe use, and consumers on request within 45 days. The material also carries UN number 3082, and a German WGK rating of 3.
