Octylisothiazolinone (2-octyl-isothiazol-3(2 H)-one) is a chemical compound that belongs to the class of isothiazolinones, broad-spectrum microbicides. 

Octylisothiazolinone is a synthetic preservative primarily used in cosmetic, personal care, and industrial products to prevent the growth of bacteria, fungi, and mold. This ingredient is highly effective at low concentrations and is used to extend the shelf life of products by preventing microbial contamination. It is widely used in water-based products, such as shampoos, body washes, and cleaning agents.

Chemical Composition and Structure
Octylisothiazolinone belongs to the isothiazolinone family, a group of chemical compounds known for their strong antimicrobial properties. The chemical structure of Octylisothiazolinone includes an isothiazolinone ring attached to an octyl alkyl chain, which gives it long-lasting action and stability in cosmetic and industrial formulations.

Physical Properties
It typically appears as a clear or slightly yellowish liquid. It is soluble in various organic solvents and can be dispersed in aqueous solutions. Octylisothiazolinone is particularly stable across a range of temperatures and pH levels, making it suitable for many applications in cosmetics and personal care products.

Production Process
Octylisothiazolinone is synthetically produced through the reaction of isothiocyanates with other chemicals to form the isothiazolinone ring, followed by the addition of an octyl chain to enhance its lipophilicity and durability. The final product is purified for use in industrial and cosmetic applications.

The name describes the structure of the molecule:

• Octyl refers to the octyl group, which is a functional group consisting of 8 carbon atoms. It is derived from octane, which has the formula C8H18.
• Isothiazolinone is a type of heterocycle that contains a five-member ring composed of three carbon atoms, a nitrogen atom, and a sulfur atom. Isothiazolinones are often used as biocides.

Description of raw materials used in production:

• 2-Octanone - A ketone used as a starting point for the synthesis of octylisothiazolinone.
• Hydrochloric acid and Carbon disulfide - These reagents are utilized in the formation of the isothiazolinone ring.

The synthesised extraction process takes place in three steps:

• Formation of the isothiazolin ring. The first step involves the reaction of an amine, such as ammonia or a primary or secondary amine, with carbon disulphide in a process known as the Willgerodt-Kindler reaction. A dithiocarbamate salt is thus formed.
• Oxidation. The dithiocarbamate salt is oxidised using hydrogen peroxide or another suitable oxidising agent. An isothiazolinone ring is thus formed.
• Alkylation. The third and final step involves the formation of an octyl group: Octylisothiazolinone is thus formed.

It occurs in the form of a clear yellow transparent thick liquid.

What it is used for and where

Octylisothiazolinone is a biocide, i.e. it can kill microorganisms. It is often used as a preservative in products such as paints, coatings and personal care products to prevent the growth of bacteria and fungi. It is effective at very low concentrations and is active against a wide range of microorganisms. However, it can cause allergic reactions in some people, so its use is regulated in many countries.

Cosmetics

Octylisothiazolinone is a preservative, antibacterial and fungicide used by cosmetic industry and in cleaning products and commonly used to control the growth of microorganisms such as fungi, bacteria, and yeasts in water cooling systems and cosmetics.

• Antimicrobial agent. This ingredient is able to suppress or inhibit the growth and replication of a broad spectrum of microorganisms such as bacteria, fungi and viruses by making the stratum corneum temporarily bactericidal and fungicidal.

Other uses

It is also used as a preservative in polymer-based paints and to prevent the growth of moulds and bacteria.

It belongs to the group of biocides regulated by the European Union (1).

Commercial applications  

Preservative in Cosmetic Products. Octylisothiazolinone is used to prevent microbial growth in cosmetic products, extending their shelf life.

Preservative in Hair Care Products. It is used in shampoos, conditioners, and other hair products to keep the formula stable and free of microbes.

Preservative in Cleaning Products. It is used in detergents, soaps, and other cleaning products to prevent microbial contamination.

Preservative in Household Products. It is used in paints, adhesives, and other household products to prevent the growth of fungi and bacteria.

Studies

Among others, 2-octyl-isothiazol-3(2H)-one (OIT) is used as a film preservative in aqueous polymer resin paints and serves to prevent the growth of moulds and bacteria. It is known that biocides leach from facades with rainwater and end up in the environment through rainwater runoff. In the present study, leaching and where OIT used in façade coatings will disperse were determined under natural conditions. Potential phototransformation products were initially identified in laboratory experiments using UV light. Subsequently, the leaching of OIT and seven degradation products were studied on artificial walls equipped with organic top coats formulated with OIT. A mass balance, including the amounts of leached and residual OIT and its seven transformation products, can explain up to 40% of the initial amount of OIT. The OIT remaining in the material after 1.5 years is by far the largest fraction. The study shows that in the assessment of biocides in the lining material, transformation products have to be taken into account both in the leachate and in the material. In addition, in the case of volatile degradation products, emissions to the air could be relevant (2).

Insecticides. The two most commonly used constituents in insecticides aimed at combating whiteflies and aphids are chloromethylisothiazolinone and methylisothiazolinone, which are used at concentrations below or at least similar to the upper limit of these chemical compounds permitted in cosmetic products.  In this study, it is considered that octylisothiazolinone can also be used to combat whitefly and green peach aphid with an acceptable level of toxicity (3).

Safety

Cases of allergy to the product have been reported (4).

In view of the exceptionally high incidence of contact allergy to the preservative methylisothiazolinone, this study deemed it necessary to know the reactivity between methylisothiazolinone, octylisothiazolinone and benzisothiazolinone. The results indicate that individuals sensitised to methylisothiazolinone may react to octylisothiazolinone and benzisothiazolinone if exposed to sufficient concentrations (5).

Health and Safety Considerations

Safety in Use
Octylisothiazolinone is effective at very low concentrations, but it can cause sensitization or skin irritation in some individuals, particularly those with sensitive skin. For this reason, its concentration in cosmetic products is strictly regulated, especially in leave-on products.

Allergic Reactions
Allergic reactions to Octylisothiazolinone are possible, particularly in individuals prone to contact dermatitis. Due to the risk of sensitization, limited use and adherence to maximum concentration guidelines set by regulatory authorities are recommended.

Toxicity and Carcinogenicity
There is no evidence that Octylisothiazolinone is carcinogenic. However, prolonged use or exposure to high concentrations can lead to skin irritation. It is important to follow safety guidelines on maximum allowable concentrations to avoid irritation risks.

Environmental and Safety Considerations
Octylisothiazolinone is not easily biodegradable and can accumulate in the environment, particularly in aquatic ecosystems, where it may negatively impact wildlife. Therefore, it should be used cautiously, and environmental regulations should be followed to limit its release into the environment.

Regulatory Status
The use of Octylisothiazolinone in cosmetic and industrial products is regulated in many regions, including the European Union and the United States. In Europe, strict limits are imposed on the concentration of this preservative in cosmetic products, especially in leave-on formulations, to reduce the risk of sensitization.

The most relevant studies on this chemical compound have been selected with a summary of their contents:

Octylisothiazolinone studies

Typical optimal characteristics of the commercial product 2-N-octyl-4-isothiazolin-3-one

• Molecular Formula : C₁₁H₁₉NOS
• Molecular Weight : 213.339
• CAS : 26530-20-1
• UNII 4LFS24GD0V
• EC Number: 247-761-7
• DSSTox Substance ID: 
• MDL number  MFCD00072473
• PubChem Substance ID   329756598
• InChI=1S/C11H19NOS/c1-2-3-4-5-6-7-8-10-11(13)9-14-12-10/h2-9H2,1H3 
• PILWLJVFXLZGMS-UHFFFAOYSA-N     
• SMILES    CCCCCCCCC1=NSCC1=O
• IUPAC   3-octyl-1,2-thiazol-4-one
• ChEBI  

Synonyms :

• 2-Octyl-4-isothiazolin-3-one
• 2-Octyl-3-isothiazolone
• EINECS 247-761-7
• 4-Isothiazolin-3-one, 2-octyl-
• Octyl-3(2H)-isothiazolone
• 3(2H)-Isothiazolone, 2-octyl-

References____________________________________________________________________

(1) European Parliament and Council. REGULATION (EC) No. 1223/2009 on cosmetic products. Official Journal of the European Union L342, 59–209 (2009).

(2) Bollmann UE, Minelgaite G, Schlüsener M, Ternes TA, Vollertsen J, Bester K. Photodegradation of octylisothiazolinone and semi-field emissions from facade coatings. Sci Rep. 2017 Jan 27;7:41501. doi: 10.1038/srep41501. 

Abstract. Amongst others, 2-octyl-isothiazol-3(2 H)-one (OIT) is used as film preservative in water-based polymer resin paints and renders to prevent the growth of moulds and bacteria. It is known that biocides leach from facades with rainwater and end up in the environment via stormwater runoff. In the present study the leaching and fate of OIT used in facade coatings was determined under natural conditions. Potential phototransformation products were initially identified in laboratory experiments using UV-light. Afterwards, the leaching of OIT and seven degradation products were studied on artificial walls equipped with organic top coatings formulated with OIT. A mass balance, including the leached and remaining amounts of OIT and its seven transformation products, can explain up to 40% of the initial amount of OIT. The OIT remaining in the material after 1.5 yr is by far the largest fraction. The study shows that in the assessment of biocides in coating material, transformation products need to be taken into account both in leachate and remaining in the material. Furthermore, in case of volatile degradation products, the emissions to air might be relevant.

(3) He W, Pan L, Han W, Wang X. Isothiazolinones as Novel Candidate Insecticides for the Control of Hemipteran Insects. Antibiotics (Basel). 2021 Apr 14;10(4):436. doi: 10.3390/antibiotics10040436.

Abstract. Hemipteran insects, such as whiteflies, aphids and planthoppers, resemble one of the most important pest groups threating food security. While many insecticides have been used to control these pests, many issues such as insecticide resistance have been found, highlighting the urgent need to develop novel insecticides. Here, we first observed that a commercial tetramycin solution was highly effective in killing whitefly. The major bioactive constituents were identified to be isothiazolinones, a group of biocides. We then tested the toxicity of several isothiazolinones to five hemipteran insects. The results show that Kathon, a widely used biocide against microorganisms, and its two constituents, chloromethylisothiazolinone (CMIT) and methylisothiazolinone (MIT), can cause considerable levels of mortality to whiteflies and aphids when applied at concentrations close to, or lower than, the upper limit of these chemicals permitted in cosmetic products. The results also indicate that two other isothiazolinones, benzisothiazolinone (BIT) and octylisothiazolinone (OIT) can cause considerable levels of mortality to whitefly and aphids but are less toxic than Kathon. Further, we show that Kathon marginally affects whitefly endosymbionts, suggesting its insecticidal activity is independent of its biocidal activity. These results suggest that some isothiazolinones are promising candidates for the development of a new class of insecticides for the control of hemipteran pests.

(4) Raison-Peyron N, Amsler E, Pecquet C, Du-Thanh A, Naessens T, Apers S, Aerts O. Severe allergic contact dermatitis caused by octylisothiazolinone in a leather sofa: two new cases. Contact Dermatitis. 2017 Sep;77(3):176-178. doi: 10.1111/cod.12793.

(5) Schwensen JF, Menné Bonefeld C, Zachariae C, Agerbeck C, Petersen TH, Geisler C, Bollmann UE, Bester K, Johansen JD. Cross-reactivity between methylisothiazolinone, octylisothiazolinone and benzisothiazolinone using a modified local lymph node assay. Br J Dermatol. 2017 Jan;176(1):176-183. doi: 10.1111/bjd.14825.