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Chloromethylisothiazolinone, also referred to as MCI, is the organic compound with the formula S(C2HCl)C(O)N(CH3).
Chloromethylisothiazolinone is a white solid that melts near room temperature.
Chloromethylisothiazolinone is an isothiazolinone, a class of heterocycles used as biocides.
CAS Number: 26172-55-4
Molecular Formula: C4H4ClNOS
Molecular Weight: 149.6
EINECS Number: 247-500-7
Synonyms:5-Chloro-2-methyl-4-isothiazolin-3-one, 26172-55-4, Methylchloroisothiazolinone, CMIT, 5-Chloro-2-methyl-3(2H)-isothiazolone, 5-Chloro-2-methyl-3-isothiazolone, Kathon CG 5243, 3(2H)-Isothiazolone, 5-chloro-2-methyl-, 5-chloro-N-methylisothiazolone, 5-chloro-2-methylisothiazolin-3-one, 5-chloro-n-methylisothiazolin-3-one, HS 818, n-methyl-5-chloroisothiazolone, DEL7T5QRPN, 4-ISOTHIAZOLIN-3-ONE, 5-CHLORO-2-METHYL-, N-Methyl-5-chloroisothiazolin-3-one, DTXSID9034286, 5-chloro-2-methyl-3(2H)-isothiazolinone, DTXCID7014286, HS-818, 247-500-7, Chloromethylisothiazolinone, 5-Chloro-2-methyl-2H-isothiazol-3-one, MFCD00792550, 5-chloro-2-methyl-1,2-thiazol-3-one, 5-chloro-2-methyl-4-isothiazoline-3-one, 5-chloro-2-methyl-isothiazol-3-one, CHEBI:53621, 2,3-Dihydro-2-methyl-3-oxo-5-chloroisothiazole, NCGC00181041-01, Bioace, 5-chloro-2-methyl-1,2-thiazol-3(2H)-one, 5-Chloro-2-methyl-3-isothiazolone (~90%), Kathon IXE, 5-Chloro-2-methyl-4-isothiazolin-3-one, tech grade, >14% in water. CMI/MI >2.0, 5-chloro-2-methyl-2,3-dihydro-1,2-thiazol-3-one, 5-chloro-2-methylisothiazol-3(2h)-one, 5-Chloro-2-methyl-4-isothiazolin-3-one 100 microg/mL in Acetonitrile, N-Methyl-5-chloroisothiazolone (5-Chloro-2-methyl-4-isothiazolin-3-one), CAS-26172-55-4, A 33 (bactericide), UNII-DEL7T5QRPN, HS 818 (antiseptic), EINECS 247-500-7, BRN 1210149, Isothiazolinones, 5-Chloro-2-methyl-4-isothiazolin-3-one D3 (methyl D3), 5-Chloro-2-methyl-4-isothiazolin-3-one (CMI), 2-Methyl-5-chloro-3-isothiazolone, 2-Methyl-5-chloroisothiazolin-3-one, 5-chloro-2-methyl-2h-isothiazolin-3-one, T 360, SCHEMBL20686, CHEMBL1738962, HSDB 8270, MSK2157, EDC61134, Tox21_112689, Tox21_300199, AKOS006230760, CS-W022348, DB14197, FC20025, GS-3223, HY-W041608, METHYLCHLOROISOTHIAZOLINONE [II], METHYLCHLOROISOTHIAZOLINONE [MI], 5-Chloro-2-methyl-4-isothiazol-3-one, 5-CHLORO-2-METHYL-4-ISOTHIAZOLIN-3-ONE (ACTIVE INGREDIENT >14%, CMI/MI 2.5 - 4.0), NCGC00181041-02, NCGC00254127-01, 55965-84-9 CMIT, MIT, METHYLCHLOROISOTHIAZOLINONE [VANDF], 2682-20-4 MIT, 5-Chloro-2-methyl-isothiazol-3(2H)-one, METHYLCHLOROISOTHIAZOLINONE [MART.], DB-007017, METHYLCHLOROISOTHIAZOLINONE [WHO-DD], NS00000256, 5-CHLOR-2-METHYL-4-ISOTHIAZOLIN-3-ONE, H10371, SBI-0654074.0001, EN300-7409393, Q204121, SR-01000944864, SR-01000944864-1, Z2417817741, 5-Chloro-2-methyl-4-isothiazolin-3-one (CMI/MI > 2.0), 5-Chloro-2-methyl-3-isothiazolone - Active Ingredient >14%, CMI/MI 2.5 - 4.0, 4-Isothiazolin-3-one,5-chloro-2-methyl-, 5-chloro-2-methyl-3(2h)-isothiazolon, 5-chloro-2-methyl-4-isothiazolin-3-on, Isothiazolinone, 5-Chloro-2-methyl-4-isothiazolinone, 5-CHLORIDE-2-METHYL-4-ISOTHIAZOLINE-3-KETONE, 5-CHLORO-2-METHYL-4-ISOTHIAZOLIN-3-ONE (CMI), 5-CHLORO-2-METHYL-3(2H)-ISOTHIAZOLONE MIXED WITH 2-METHYL-3(2H)ISOTHIAZOLONE
Chloromethylisothiazolinone is a heterocyclic chemical compound related to isothiazole.
Chloromethylisothiazolinone is an antimicrobial preservative that is often used to control fungi, bacteria, and algae. Since water-containing solutions are the breeding grounds for bacteria, isothiazolinone can easily be used in such solutions.
These compounds have an active sulphur moiety that is able to oxidize thiol-containing residues, thereby effectively killing most aerobic and anaerobic bacteria.
Chloromethylisothiazolinone is often used in combination with methylisothiazolinone, a mixture known as Kathon.
The isothiazolinones have attracted attention because they can cause contact dermatitis.
Chloromethylisothiazolinone is effective against gram-positive and gram-negative bacteria, yeast, and fungi.
Chloromethylisothiazolinone, more commonly referred to as CMIT or by its full chemical name 5-Chloro-2-methyl-4-isothiazolin-3-one, is a synthetic heterocyclic organic compound that belongs to the family of isothiazolinones, which are widely known for their strong antimicrobial properties.
Chloromethylisothiazolinone is most often encountered as part of a mixture with a closely related compound, methylisothiazolinone (MIT), and together they are sold under trade names such as Kathon CG.
This combination has been used extensively as a preservative and biocide in personal care products, cleaning agents, paints, adhesives, and various industrial water treatment systems.
Chloromethylisothiazolinone is structured around an isothiazolinone ring system substituted with a chlorine atom and a methyl group, which gives it enhanced antimicrobial activity.
Its effectiveness stems from its ability to disrupt microbial enzyme systems and interfere with vital cellular processes, thereby killing or inhibiting the growth of bacteria, fungi, and algae at very low concentrations. Because of this potent activity, CMIT has been valued for decades as an ingredient that prevents microbial contamination and extends the shelf life of products that would otherwise be vulnerable to spoilage or biofilm formation.
In consumer products, Chloromethylisothiazolinone has historically been used in shampoos, conditioners, lotions, liquid soaps, and other cosmetics, where it served as a preservative to prevent microbial growth in water-based formulations.
In industrial settings, it is found in paints, coatings, adhesives, paper manufacturing, and cooling water systems, where it protects large-scale materials and processes against microbial degradation.
Its role in such applications is critical for maintaining product stability, preventing discoloration or odor caused by microbial activity, and ensuring hygienic safety during use.
Chloromethylisothiazolinone that is 4-isothiazolin-3-one bearing a methyl group on the nitrogen atom and a chlorine at C-5.
Chloromethylisothiazolinone is a powerful biocide and preservative and is the major active ingredient in the commercial product KathonTM.
Chloromethylisothiazolinone and Methylchloroisothiazolinone (CMIT) may be hard to pronounce, but they can be even harder on the body.
These common preservatives are found in many liquid personal care products, and have been linked to lung toxicity, allergic reactions, and possible neurotoxicity.
Chloromethylisothiazolinone is a biocide that is effective against both gram-positive and gram-negative bacteria, yeast, and fungus.
It is often found in water-based personal care and cosmetics, as well as adhesives, detergents, paints, fuels, and industrial operations.
Chloromethylisothiazolinone is frequently used in conjunction with other preservatives such as ethylparaben, benzalkonium chloride, bronopol, and phenoxyethanol.
Melting point : 42–45 °C
Boiling point : 109.7 °C
Density : 1.25 (14% aq.)
Refractive index : n20/D 1.378
Storage temp. : Refrigerator
Solubility : Slightly soluble in chloroform, DMSO, methanol (heated)
pKa : –4.06 ± 0.40 (predicted)
Form : Liquid
Color : White
Odor : Pungent, aromatic odor
Stability : Stable; incompatible with strong oxidizing agents
InChI : InChI=1S/C4H4ClNOS/c1-6-4(7)2-3(5)8-6/h2H,1H3
InChIKey : DHNRXBZYEKSXIM-UHFFFAOYSA-N
SMILES : S1C(Cl)=CC(=O)N1C
LogP : 0.240 (estimated)
Chloromethylisothiazolinone is contained, along with methylisothiazolinone (MI), in Kathon cosmetic grade (CG) and MCI/MI.
Chloromethylisothiazolinone is irritant and sensitizer.
Chloromethylisothiazolinone that is 4-isothiazolin-3-one bearing a methyl group on the nitrogen atom and a chlorine at C-5.
Chloromethylisothiazolinone is a powerful biocide and preservative and is the major active ingredient in the commercial product KathonTM.
Due to a lack of toxicity information on this particular chemical, the screening level is being established under R232(i) at 0.1 μg/m3 with annual averaging.
Chloromethylisothiazolinone can cause allergic reactions in some people.[4] The first publication of the preservative as a contact allergen was in 1988.
Cases of photoaggravated allergic contact dermatitis, i.e. worsening of skin lesions after sun exposure, have also been reported.
In pure form or in high concentrations, Chloromethylisothiazolinone is a skin and membrane irritant and causes chemical burns.
In the United States, maximum authorized concentrations are 15 ppm in rinse-offs (of a mixture in the ratio 3:1 of 5-chloro-2-methylisothiazol 3(2H)-one and 2-methylisothiazol-3 (2H)-one).
In Canada, Chloromethylisothiazolinone may only be used in rinse-off products in combination with methylisothiazolinone, the total concentration of the combination may not exceed 15 ppm.
Methylisothiazolinone is considered safe in the allowed amount in rinse-off products (0.01%) and safe in leave-in products when formulated to be non-sensitizing.[8]
However, despite its widespread utility, Chloromethylisothiazolinone is also recognized as a strong skin sensitizer and allergen.
Repeated or prolonged exposure, even at very low concentrations, can lead to allergic contact dermatitis in sensitive individuals.
This has been a major issue in cosmetics and personal care products, where consumer exposure is direct and frequent.
As a result, regulatory agencies such as the European Union (EU) and other international health authorities have significantly restricted or banned the use of CMIT (and its mixture with MIT) in leave-on cosmetics and limited its concentrations in rinse-off products.
In occupational settings, improper handling of concentrated forms can cause severe skin irritation, eye damage, and respiratory distress if inhaled as aerosols or vapors.
In summary, Chloromethylisothiazolinone is a powerful antimicrobial preservative that has played an important role in protecting both consumer goods and industrial systems from microbial contamination.
Yet, its strong sensitization potential and toxicity concerns have also made it a controversial chemical, leading to regulatory restrictions and reformulations in many industries.
Chloromethylisothiazolinones use continues mainly in industrial applications and controlled product types, where its effectiveness can be harnessed while exposure risks are carefully managed.
An overdose of Kathon by aircraft maintenance personnel, using 38 times the correct amount, resulted in damage to both engines of a Titan Airways aircraft in February 2020.
After losing both engines in succession, the Airbus A321 made an emergency landing at London Gatwick Airport.
The maintenance procedures specified the Kathon to be diluted to 100 PPM by volume, but with the aircraft maintenance technician being unfamiliar with the term "PPM" and the term not being defined in the aircraft maintenance manuals, the technician instead used an online calculator to convert PPM to percentages, misinterpreted the answer, and added 30 kg of Kathon to each wing tank, which was over 38 times the required amount.
Over the course of the next day, the Kathon progressively caused more and more damage to the engines, finally resulting in an emergency landing.
Uses Of Chloromethylisothiazolinone:
Although isothiazolinones have no direct applications, their derivatives such as 5-chloro-2-methyl-4-isothiazolin-3-on and 2-methyl-4-isothiazolin-3 which are used together as preservatives in commercial households and cosmetics products, for instance, cleaners, shampoos, and washing materials.
Notably, various products that use isothiazolinones are in the market, including shampoo, hand sanitizer, and lotions.
Chloromethylisothiazolinone is used in these products as an inhibitor of microbial activity that could lead to the product spoiling before the expected expiration date.
Chloromethylisothiazolinone is a high performance biocide for preserving metal working fluids, hydraulic fluids, polymer emulsions, pigment dispersions.
Chloromethylisothiazolinone is a cost-effective antimicrobial for personal care formulations. Suggested applications: personal care preservative.
Chloromethylisothiazolinone is a high performance industrial microbiocide for use in recirculating water cooling towers, wood, mold and mildew control, pulp and paper mills, air washer systems.
A isothiazolidin-3-one derivative as antimicrobial.
Chloromethylisothiazolinone was tested for inhibition of PCAF activity.
Chloromethylisothiazolinone showed the most potent inhibition of PCAF.
Methylchloroisothiazolinone is found in many water-based personal care products and cosmetics.
Chloromethylisothiazolinone was first used in cosmetics in the 1970s. It is also used in glue production, detergents, paints, fuels, and other industrial processes.
Chloromethylisothiazolinone is known by the registered tradename Kathon CG when used in combination with methylisothiazolinone.
Methylchloroisothiazolinone may be used in combination with other preservatives including ethylparaben, benzalkonium chloride, bronopol and phenoxyethanol.
Chloromethylisothiazolinone is primarily used as a broad-spectrum antimicrobial preservative because it can kill or inhibit the growth of a wide variety of microorganisms such as bacteria, fungi, and algae, even when added in very small amounts, making it especially valuable in water-based products that would otherwise be prone to microbial contamination.
In the personal care and cosmetic industry, Chloromethylisothiazolinone has historically been incorporated into products such as shampoos, conditioners, liquid soaps, body washes, and lotions, where its role was to extend the shelf life of formulations and ensure that the products remained free of microbial growth during storage and consumer use.
It has also been used in certain household cleaning products and detergents for the same reason, since its presence helps maintain product safety and stability in environments where moisture and organic materials can easily promote microbial proliferation.
In the industrial and manufacturing sectors, Chloromethylisothiazolinone is applied more extensively due to its effectiveness and cost-efficiency as a preservative and biocide.
Chloromethylisothiazolinone is added to paints, adhesives, coatings, and sealants to prevent microbial degradation, which would otherwise lead to unpleasant odors, color changes, loss of performance, or product spoilage.
In the paper and pulp industry, it helps control microbial contamination during processing, thus improving product quality and reducing equipment fouling.
Similarly, in oilfield operations, cooling water systems, and other water treatment facilities, Chloromethylisothiazolinone is used to control bacterial slime formation and biofilm buildup, which can cause blockages, corrosion, and efficiency losses in large-scale systems.
Because of its broad-spectrum activity, Chloromethylisothiazolinone is also used in household products and industrial cleaning formulations, where it acts not only as a preservative but also as a disinfectant, ensuring that cleaning solutions remain effective for longer periods.
Its inclusion in such products helps reduce the growth of harmful microorganisms on treated surfaces, thereby contributing to hygiene and safety in both domestic and professional environments.
Although its use in consumer cosmetics has been heavily restricted in many regions due to its sensitizing and allergenic properties, Chloromethylisothiazolinone remains an important preservative in technical, industrial, and controlled-use applications, where its antimicrobial strength and stability provide significant advantages over many alternative chemicals.
Safety Profile Of Chloromethylisothiazolinone:
The recommended use of isothiazolinone products by the manufacturers used as wrinkle releaser is not harmful.
However, allergy to skin is one of the most reported issue with isothiazolinone.
Chloromethylisothiazolinone is considered a hazardous chemical because of its potential to cause harm to both human health and the environment when not handled or formulated properly.
One of the most significant hazards associated with Chloromethylisothiazolinone is its strong skin-sensitizing properties.
Even at very low concentrations, it can trigger allergic contact dermatitis, especially in sensitive individuals.
Repeated or prolonged exposure to products containing Chloromethylisothiazolinone may lead to redness, itching, rashes, and chronic skin conditions that persist long after the initial exposure.
This is one of the primary reasons why its use in cosmetics and personal care products has been restricted or banned in many regions, including the European Union.
In addition to its skin effects, Chloromethylisothiazolinone can cause eye irritation and damage, especially if it comes into direct contact with the eyes in concentrated form.
Splashes or accidental exposure to concentrated solutions may result in pain, redness, swelling, and in severe cases, long-term injury to ocular tissues.
Inhalation of vapors, mists, or aerosols containing Chloromethylisothiazolinone may also lead to respiratory irritation, causing symptoms such as coughing, throat discomfort, or difficulty breathing.
Workers in industrial environments where CMIT is handled in bulk or sprayed are at greater risk of these hazards if proper protective measures are not taken.
Chloromethylisothiazolinone is also classified as a toxic substance if ingested, as it can cause gastrointestinal distress, nausea, vomiting, and systemic toxicity.
Although accidental ingestion is unlikely for the general public due to its limited presence in consumer goods today, improper handling or exposure in industrial settings poses real risks.
