Hydroxyisohexyl 3-cyclohexene carboxaldehyde is a synthetic mixture of two isomers.

The name describes the structure of the molecule:

• "Hydroxyisohexyl" refers to an isoxyl group (a branched chain of 6 carbon atoms) with a hydroxyl (-OH) functional group attached. This part of the molecule contributes to its solubility and reactivity.
• "3-cyclohexene" means a cycloesene (a six-member ring with a double bond) in the third position of the molecule.
• "Carboxaldehyde" is a functional group consisting of a carbonyl center (a double carbon bound to oxygen) with the carbon atom also bound to the hydrogen atom. Aldehydes are often responsible for the fragrance in various scents and flavors.

The synthesis process takes place in several stages:

• Formation of the cycloesene ring. The cycloesene ring can be synthesized through various methods, one of which is the cyclization of a suitable precursor such as 1,6-diene.
• Introduction of the hydroxyisoxysilic group. The hydroxyisoxysilic group can be introduced through a reaction known as hydroxyalkylation. This involves the reaction of the cycloesene ring with an appropriate reagent, such as isohexyl alcohol, under appropriate conditions.
• Formation of the carboxaldehyde group. The carboxaldehyde group can be introduced through a process known as oxidation. This involves the reaction of hydroxyisohexyl-cyclohexene with an oxidizing agent, which results in the formation of the aldehyde group.

It appears as a colourless liquid.

Cosmetics

Hydroxyisohexyl 3-cyclohexene carboxaldehyde is a restricted ingredient II/1380 as a Relevant Item in the Annexes of the European Cosmetics Regulation No. 1223/2009.

Fragrance. It plays a decisive and important role in the formulation of cosmetic products as it provides the possibility of enhancing, masking or adding fragrance to the final product, increasing its marketability. Consumers always expect to find a pleasant or distinctive scent in a cosmetic product.

Perfuming. Unlike fragrance, which may contain slightly less pleasant or characteristic odors, the term perfume denotes only very pleasant scents.

Commercial applications  

Fragrance Ingredient. Hydroxyisohexyl 3-Cyclohexene Carboxaldehyde is used to scent various cosmetic and personal care products.

Fragrance Stabilizer. Used to prolong the scent duration in fragranced products.

Masking Agent. It can be used to mask unpleasant odors in cosmetic formulations.

Use in Perfumery. Used as a component in various fragrances to impart a fresh and clean scent.

Safety

In 2014, the fragrance hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) was excluded from the Swedish baseline series (1).

In this study of 6004 patients, 940 (15.7%, 95%CI: 14.7-16.6%) were fragrance-sensitized. Regarding the single fragrances, most patients were sensitized to Lin-OOH (3.9%), Evernia furfuracea (3.0%), Lim-OOH (2.5%), and hydroxyisohexyl 3-cyclohexene carboxaldehyde (2.1%) (2).

In a survey of 12377 aged between 18 and 74, in five different European countries (Sweden, the Netherlands, Germany, Italy and Portugal) Hydroxyisohexyl 3-cyclohexene carboxaldehyde was used as a test (3).

• Molecular Formula   C₁₃H₂₂O₂
• Molecular Weight   210.317 g/mol
• CAS   31906-04-4    51414-25-6
• UNII    QUE43B9Z2Q
• EC number   250-863-4    257-187-9 

Synonyms:

• 4-(4-Hydroxy-4-methylpentyl)cyclohex-3-ene-1-carbaldehyde
• Lyral®
• EINECS 250-863-4
• Kovanol
• Mugonal
• Landolal
• 3-Cyclohexene-1-carboxaldehyde, 4-(4-hydroxy-4-methylpentyl)-
• 4-(4-Hydroxy-4-methylpentyl)-3-cyclohexene-1-carboxaldehyde
• 4-(4-Hydroxy-4-methylpentyl)cyclohex-3-enecarbaldehyde

References_________________________________________________________________________

(1) Engfeldt M, Hagvall L, Isaksson M, Matura M, Mowitz M, Ryberg K, Stenberg B, Svedman C, Bruze M. Patch testing with hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) - a multicentre study of the Swedish Contact Dermatitis Research Group.  Contact Dermatitis. 2017 Jan;76(1):34-39. doi: 10.1111/cod.12699. 

(2) Bennike NH, Zachariae C, Johansen JD. Non-mix fragrances are top sensitizers in consecutive dermatitis patients - a cross-sectional study of the 26 EU-labelled fragrance allergens. Contact Dermatitis. 2017 Nov;77(5):270-279. doi: 10.1111/cod.12822. 

(3) Diepgen TL, Ofenloch RF, Bruze M, Bertuccio P, Cazzaniga S, Coenraads PJ, Elsner P, Goncalo M, Svensson Å, Naldi L. Prevalence of contact allergy in the general population in different European regions.  Br J Dermatol. 2016 Feb;174(2):319-29. doi: 10.1111/bjd.14167.