2-Benzisothiazolin-3-one (BIT)
BIT Structural Formula: [Image/Diagram]; Appearance: White or pale yellow powder; Molecular Weight: 151; Melting Point: 156°C; Solubility: Soluble in hot water; slightly soluble in certain organic solvents. This product exhibits high thermal stability; differential thermal analysis indicates that, with a controlled heating rate of 4°C/min, only slight weight loss begins at 180°C, with significant weight loss occurring only at 250°C. It is stable under both acidic and alkaline conditions and can be utilized across a wide pH range. BIT demonstrates high bactericidal efficiency and a broad spectrum of activity, proving effective against bacteria, molds, yeasts, and algae; it also exhibits high activity against common sulfate-reducing bacteria. For the raw BIT powder, the Minimum Inhibitory Concentration (MIC) against the vast majority of microorganisms is below 20 mg/L. The product possesses a favorable safety profile; its oral LD50 in rats exceeds 1400 mg/kg, classifying it as a low-toxicity substance. It is biodegradable, and its safety has been recognized by relevant regulatory bodies in numerous countries (e.g., the U.S. FDA, U.S. EPA, Germany's BGA, Japan's MITI, etc.), establishing it as one of the safest biocides and preservatives available.
BIT is a novel industrial biocide characterized by its broad spectrum, high efficiency, low toxicity, and excellent water solubility. Typically, an addition level of just 0.01–0.05% is sufficient to achieve ideal bactericidal and preservative effects. Reports indicate that adding 0.05% BIT to water-based latex paints prevents microbial growth for a period of 100 days. J.N. Edwards and colleagues conducted a large-scale comparative evaluation of biocides intended for use in both interior and exterior latex paints. They organized a consortium of seven companies to test and evaluate 22 commercially available preservatives, 13 of which were assessed specifically for use in interior latex paints. The results indicated that, for use in matte PVA latex paints, four preservatives performed particularly well-with BIT being one of them. To assess the long-term efficacy (persistence) of the preservatives, microbial cultures were inoculated into the samples at regular intervals throughout the testing period (a total of three inoculations); in every instance, BIT demonstrated potent bactericidal activity. In the context of PAA latex semi-gloss paints, only BIT-along with phenylmercuric acetate (a biocide historically renowned for its potent antimicrobial activity, though now banned due to its high toxicity)-demonstrates comparable efficacy; the remaining 12 tested agents performed significantly less effectively.
Since BIT remains stable at temperatures below 180°C-a threshold significantly higher than typical paint manufacturing temperatures-it can be introduced at the very inception of the paint production process, thereby ensuring the most effective inhibition of microbial growth. BIT and its formulations exhibit excellent stability, obviating the need for additional stabilizers. Furthermore, they are free of heavy metals, chlorine, formaldehyde (and formaldehyde-releasing agents), and inorganic salts; they remain stable across a broad pH range and provide long-lasting protection to the material systems being preserved. Consequently, BIT not only prevents the spoilage and deterioration of the paint itself but also endows the cured paint film with the ability to resist fungal infestation.
Methyl-4-isothiazolin-3-one (MIT) and 5-Chloro-2-methyl-4-isothiazolin-3-one (CIT)
Structural formulas for MIT and CIT: [Image/Formula]. In their pure form, these compounds are white solids soluble in water, lower alcohols, ethylene glycol, and polar organic solvents. MIT has a melting point of 48–50°C, while CIT has a melting point of 54–55°C. These are highly active biocides; for many microorganisms, their Minimum Inhibitory Concentration (MIC) falls below 10 mg/L. They exert potent biocidal and inhibitory effects against bacteria, molds, yeasts, and algae, demonstrating efficacy even at low concentrations. The safety profile of this product is favorable, with an oral LD50 in albino rats of ≥ 3350 mg/kg (for formulations containing ≤ 2% active ingredients); it is classified as a low-toxicity substance, is biodegradable, and exhibits no teratogenic or mutagenic potential. As all known manufacturing methods yield a mixture of MIT and CIT-with the ratio between the two varying within a range of 4.5 to 0.02-a particularly successful formulation consists of a mixture of CIT and MIT in an approximate ratio of 3:1; however, the addition of specific stabilizers is required to prevent their decomposition. Currently, most commercial products utilize divalent metal salts as stabilizers; however, within polymer emulsion and coating systems, the presence of metal salts can lead to "salt shock"-phenomena such as gelation or phase separation. MIT and CIT exhibit relative stability in acidic and oxidative environments; conversely, in the presence of primary amines, secondary amines, thiols, sulfides, reducing agents, or strong nucleophiles, their active ingredients may degrade and lose efficacy. Therefore, it is recommended that these substances be employed within a pH range of 2 to 9 and at temperatures below 60°C.
2-n-Octyl-4-isothiazolin-3-one (OIT)
OIT Structural Formula: [Image/Diagram]; In its pure form, it is a white solid with a melting point of 97–100°C, soluble in propylene glycol and polar organic solvents. This product possesses an excellent safety profile; its oral LD50 in albino rats is ≥ 4000 mg/kg, classifying it as a low-toxicity substance. It is biodegradable and exhibits no teratogenic or mutagenic effects. It demonstrates superior antimicrobial efficacy against a wide spectrum of bacteria, molds, yeasts, and algae-particularly exhibiting potent fungicidal activity against molds. Its mold-inhibiting performance rivals that of organomercury and organotin compounds; consequently, it is widely utilized as a dry-film fungicide in coating applications. To achieve optimal mold-inhibiting results when using OIT as a dry-film fungicide, it is essential to ensure that the formulation's pH remains ≤ 9.5, to avoid or minimize the use of talc fillers, and to refrain from incorporating sulfides (such as Lithopone).
2-Methyl-4,5-propylene-4-isothiazolin-3-one (MTI)
MTI Structural Formula: [Image/Diagram]; Melting Point: 110°C; In its pure form, it is a white amorphous solid. At ambient temperatures, it is miscible with acids, ethers, ketones, and similar substances. MTI is a highly active, broad-spectrum biocide and preservative that demonstrates effective inhibitory and eradicative activity against a diverse range of microorganisms, including *E. coli*, *Pseudomonas aeruginosa*, *Bacillus subtilis*, *Staphylococcus aureus*, and *Aspergillus niger*. MTI has a decomposition temperature of 216°C, which is significantly higher than the operational temperatures typically encountered during paint manufacturing. Consequently, this preservative can be introduced at the very beginning of the production process, thereby achieving maximum efficacy in inhibiting microbial growth. It remains stable across a wide pH range and demonstrates considerable stability in the presence of ammonium ions; given that ammonium hydroxide is frequently used to adjust pH levels during paint production, stability against ammonium ions constitutes a critical performance metric for paint preservatives. The commercial formulation of MTI is an aqueous solution; it contains no organic solvents, inorganic metal salts, chlorine, or formaldehyde. It is non-corrosive to materials commonly used in standard manufacturing operations and is compatible with both manual and automated dosing systems. Possessing exceptionally high activity, it effectively controls the proliferation of a wide spectrum of microorganisms in water-based paints, even at low dosages. Thus, this biocide combines the advantages of potent antimicrobial efficacy with minimal environmental impact, thereby fully meeting the requirements for green and eco-friendly products.
4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT)
Structural Formula of DCOIT: [Image/Formula]. It is a highly effective biocide and algicide, particularly well-suited for use in marine antifouling coatings. This product successfully passed the rigorous review process of the U.S. Environmental Protection Agency (EPA) in 1994, and subsequently received the "Presidential Green Chemistry Challenge Award"-presented jointly by the U.S. Government and the American Chemistry Council-in both 1996 and 1997. It exhibits broad-spectrum biocidal activity, effectively controlling both soft and hard marine fouling organisms. It is characterized by low toxicity and high efficiency; with a half-life of less than one hour, it degrades rapidly in seawater, undergoes extensive metabolic breakdown (classified at levels 4–5), and does not bioaccumulate within marine organisms. Furthermore, it offers long-lasting efficacy: given the unique operational demands of marine vessels and the inherent complexities of coating application, the ability of an antifouling agent to provide sustained, effective protection over time serves as a crucial benchmark for evaluating its quality. Finally, it demonstrates excellent compatibility with other coating components. Reports indicate that, among the vast array of isothiazolinone compounds currently available, DCOIT stands out as the most suitable biocide and algicide for application in marine antifouling coatings.
