Methyl 2-octynoate, also known as Methyl heptyl acetylenate, is an aromatic ester used in perfumery for its fruity fragrance. It is known to cause an allergic reaction in some people and is often mentioned on product labels to warn sensitive individuals.

The name describes the structure of the molecule

• "Methyl" indicates the methyl group (-CH₃) attached to the ester. 
• "2-octynoate" signifies the ester structure derived from 2-octynoic acid, an unsaturated acid with a triple bond.

Description of raw materials used in production

2-octynoic acid and methanol are the primary raw materials used to produce Methyl 2-octynoate through an esterification reaction.

Synthesis process

• Esterification Reaction - 2-octynoic acid reacts with methanol in the presence of an acid catalyst to produce Methyl 2-octynoate and water.
• Separation - Methyl 2-octynoate is separated from the reaction mixture.
• Purification - Any impurities are removed through appropriate methods such as distillation.
• Packaging - The purified compound is then packaged for sale or used as an ingredient in various products.

It appears as a transparent liquid.

What it is for and where

Cosmetics

Perfuming. Unlike fragrance, which can also contain slightly less pleasant or characteristic odours, the term perfume indicates only very pleasant fragrances. Used for perfumes and aromatic raw materials.

Applications

Perfumery - Due to its characteristic floral scent, it's used as a component in perfumes to give a distinctive note.

Cosmetic Products - Beyond perfumes, Methyl 2-octynoate can be found in various cosmetic products like creams, lotions, and makeup items, where it's mainly used as a fragrance agent.

Safety

It is known to produce an allergic reaction in some people and is often mentioned on product labels to warn sensitive people.

Skin Sensitisation Testing - Methyl 2-octynoate is also known to be used in dermatological tests to identify skin sensitisation.

Studies

Methyl 2-octynoate is a chemical compound much discussed in scientific literature.

According to EFSA experts Methyl 2-octynoate is neither PBT (Persistent, bioaccumulative and toxic substances) nor genotoxic (1), however, several cases of sensitisation to this chemical compound have been established (2).

• Molecular Formula  C₉H₁₄O₂
• Molecular Weight  154.21 g/mol
• CAS  111-12-6
• UNII    0TTP6YT2T3
• EC Number   203-836-6
• DTXSID9047093
• Nikkaji   J22.135J

References_____________________________________________________________________

(1) Api AM, Belsito D, Biserta S, Botelho D, Bruze M, Burton GA Jr, Buschmann J, Cancellieri MA, Dagli ML, Date M, Dekant W, Deodhar C, Fryer AD, Gadhia S, Jones L, Joshi K, Lapczynski A, Lavelle M, Liebler DC, Na M, O'Brien D, Patel A, Penning TM, Ritacco G, Rodriguez-Ropero F, Romine J, Sadekar N, Salvito D, Schultz TW, Siddiqi F, Sipes IG, Sullivan G, Thakkar Y, Tokura Y, Tsang S. RIFM fragrance ingredient safety assessment, methyl 2-octynoate, CAS Registry Number 111-12-6. Food Chem Toxicol. 2019 Dec;134 Suppl 2:110825. doi: 10.1016/j.fct.2019.110825. 

(2) Heisterberg MV, Vigan M, Johansen JD. Active sensitization and contact allergy to methyl 2-octynoate. Contact Dermatitis. 2010 Feb;62(2):97-101. doi: 10.1111/j.1600-0536.2009.01664.x. 

Abstract. Background: Methyl 2-octynoate is a synthetic fragrance which was first described to have sensitizing properties in 1935. It is one of the 26 fragrances to be labelled on the ingredient list according to current European cosmetics regulation. Objectives: To report the experience with patch testing with methyl 2-octynoate 1% and 2% in pet. Methods: 230 eczema patients were consecutively patch tested with 1% methyl 2-octynoate at department of Dermato-allergology Gentofte Hospital, Denmark and 120 eczema patients were consecutively patch tested with 2% M2O in Finn Chambers at the Départment de Dermatologie, CHU Saint Jacques, France. Results: Three cases of active sensitization were observed. 2 (0.87%) of the 230 Danish subjects tested with 1% in pet. and of the 120 French subjects patch tested with 2% in pet. 1 (0.83%). There was no statistical difference in active sensitization between the two groups (P = 0.72). Allergic contact dermatitis was observed in two patients (1.67%) in the French group and none in the Danish group. Conclusion: Contact allergy to methyl 2-octynoate was frequently seen when patch testing with 2% in pet. However, active sensitization was also observed, when patch testing with concentrations of 1% and 2% methyl 2-octynoate. The patch test concentration should be below 1% in pet., but a safe concentration remains to be defined.

Soo Lim D, Min Choi S, Kim KB, Yoon K, Kacew S, Sik Kim H, Lee BM. Determination of fragrance allergens and their dermal sensitization quantitative risk assessment (QRA) in 107 spray perfumes. J Toxicol Environ Health A. 2018;81(22):1173-1185. doi: 10.1080/15287394.2018.1543232.

Abstract. Cutaneous allergy occurs primarily as a result of using cosmetic, household, and laundry products available on the market that contain fragrances. The aim of this study was to develop a rapid and specific high-performance liquid chromatography with ultraviolet detection (HPLC-UV) method for quantification of 25 fragrance allergens (amyl cinnamyl alcohol, benzyl alcohol, benzyl benzoate, benzyl cinnamate, benzyl salicylate, citronellol, cinnamyl alcohol, citral, coumarin, eugenol, farnesol, geraniol, hydroxycitronellal, HICC (4-(4-hydroxy-4-methylpentyl)-3-cyclohexene-1-carboaldehyde), isoeugenol, isoeugenyl acetate, lilial (butyl phenyl methyl propional), limonene, linalool, methyl 2-octynoate, etc.). In addition, an exposure-based quantitative risk assessment (QRA) was performed to determine safe levels of fragrance ingredients in 107 perfumes. In 76 women's and 31 men's fragrances, 25 allergens were identified at concentrations ranging from undetectable (N.D.) to 8,997.68 mg/kg, and from N.D. to 17,352.34 mg/kg, respectively. An exposure-based sensitization QRA revealed that the ratios of acceptable exposure level (AEL) to consumer exposure level (CEL) of fragrance ingredients were greater than 1, suggesting an absence of skin sensitizing potential. However, the maximum level used in the exposure scenario was determined by the product purpose and application type, and AEL/CEL ratios of lilial, HICC, citral, isoeugenol, and methyl 2-octynoate analyzed in women's perfume were 0.53, 0.67 0.19, 0.13, and 0.57, respectively. As the ratios of AEL:CEL of these fragrance ingredients were below 1, the utilization of these potential skin sensitizers is not considered safe. Our findings indicate that the sensitization risk of allergens with AEL:CEL ratios below 1 detected in fragrances needs to be reduced to the appropriate human safety level for risk management.

English JS, Rycroft RJ. Allergic contact dermatitis from methyl heptine and methyl octine carbonates. Contact Dermatitis. 1988 Mar;18(3):174-5. doi: 10.1111/j.1600-0536.1988.tb04510.x.