Methylchloroisothiazolinone, also referred to as MCI, is the

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula S(C₂HCl)C(O)N(CH₃). It is a white solid that melts near room temperature. The compound is an

isothiazolinone Isothiazolinone (; sometimes isothiazolone) is an organic compound with the formula (CH)2SN(H)CO. A white solid, it is structurally related to isothiazole. Isothiazolone itself is of limited interest, but several of its derivatives are widely us ...

, a class of

heterocycle A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

s used as

biocide A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a sli ...

s. These compounds have an active sulphur moiety that is able to oxidize

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

-containing residues, thereby effectively killing most aerobic and anaerobic bacteria. MCI is often used in combination with

methylisothiazolinone Methylisothiazolinone (), MIT, or MI, is the organic compound with the formula S(CH)2C(O)NCH3. It is a white solid. Isothiazolinones, a class of heterocycles, are used as biocides in numerous personal care products and other industrial applicatio ...

, a mixture known as Kathon. The isothiazolinones have attracted attention because they can cause

contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes ...

. Methylchloroisothiazolinone is effective against

gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

and

gram-negative bacteria Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

, and

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

Application

Methylchloroisothiazolinone is found in many water-based personal care products and cosmetics. Methylchloroisothiazolinone was first used in cosmetics in the 1970s. It is also used in glue production, detergents, paints, fuels, and other industrial processes. Methylchloroisothiazolinone is known by the registered tradename ''Kathon'' CG when used in combination with

. Methylchloroisothiazolinone may be used in combination with other preservatives including ethylparaben,

benzalkonium chloride Benzalkonium chloride (BZK, BKC, BAK, BAC), also known as alkyldimethylbenzylammonium chloride (ADBAC) is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs have three main categories of use: ...

, bronopol and phenoxyethanol.

Hazards

Methylchloroisothiazolinone can cause allergic reactions in some people. 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, methylchloroisothiazolinone 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, methylchloroisothiazolinone 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.

Incidents

An overdose of Kathon by aircraft maintenance personnel, using 38 times the correct amount, resulted in damage to both engines of a

Titan Airways Titan Airways Limited is a British charter airline based at London Stansted Airport. The carrier specialises in short-notice ACMI (aircraft, crew, maintenance, and insurance) and wet lease operations, as well as ad-hoc passenger and cargo char ...

aircraft in February 2020. After losing both engines in succession, the

Airbus A321 The Airbus A321 is a member of the Airbus A320 family of short to medium range, Narrow-body aircraft, narrow-body, commercial passenger Twinjet, twin engine jet airliners; it carries 185 to 236 passengers. It has a stretched fuselage which was ...

made an emergency landing at

London Gatwick Gatwick Airport , also known as London Gatwick Airport (), is the secondary international airport serving London, West Sussex and Surrey. It is located near Crawley in West Sussex, south of Central London. In 2024, Gatwick was the second-bu ...

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. Aviation safety report
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References

External links

CMIT/MIT Assessment
*
Methylchloroisothiazolinone at the National Library of Medicine
{{Use dmy dates, date=February 2021 Preservatives Isothiazolinones Chloroarenes Methyl compounds