Octadecyl trimethyl ammonium chloride
[CAS# 112-03-8]

Identification

• Classification: Surfactant >> Cationic surfactant >> Quaternary ammonium salt type
• Name: Octadecyl trimethyl ammonium chloride
• Synonyms: Octadecyltrimethylammonium chloride; Steartrimonium chloride; Stearyl trimethyl ammoium chloride; Trimethyloctadecylammonium chloride; Aliquat 7
• Molecular Formula: C₂₁H₄₆N^.Cl
• Molecular Weight: 348.05
• CAS Registry Number: 112-03-8
• EC Number: 203-929-1
• SMILES: CCCCCCCCCCCCCCCCCC[N+](C)(C)C.[Cl-]

Safety Data

• Hazard Symbols: GHS05;GHS06;GHS07;GHS09 Danger
• Hazard Statements: H302-H311-H312-H314-H318-H400-H410
• Precautionary Statements: P260-P262-P264-P264+P265-P270-P273-P280-P301+P317-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P321-P330-P361+P364-P362+P364-P363-P391-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Skin corrosion	Skin Corr.	1C	H314
Acute toxicity	Acute Tox.	3	H311
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H312
Skin corrosion	Skin Corr.	1B	H314
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H332
Eye irritation	Eye Irrit.	2	H319

Discovory and Applicatios

Octadecyl trimethyl ammonium chloride is a quaternary ammonium compound consisting of a quaternary nitrogen atom bonded to an octadecyl (C₁₈) alkyl chain and three methyl groups, with chloride as the counterion. It belongs to the class of cationic surfactants that were developed during the 20th century for their dual properties of surface activity and antimicrobial action. The long hydrophobic octadecyl chain allows strong adsorption to negatively charged surfaces, while the cationic headgroup disrupts microbial membranes, resulting in bactericidal and fungicidal effects. These properties led to its early adoption in sanitation and disinfection applications.

The compound has been widely applied in industrial and household disinfectants, water treatment, and cleaning products. Its ability to reduce surface tension allows it to penetrate soils and residues, while simultaneously providing antimicrobial protection. Octadecyl trimethyl ammonium chloride exhibits broad-spectrum activity against Gram-positive and Gram-negative bacteria as well as some fungi, which makes it particularly effective for healthcare, food processing, and institutional cleaning applications. Its stability in a wide pH range and resistance to hydrolysis contribute to its versatility in diverse formulation conditions.

In personal care products, octadecyl trimethyl ammonium chloride is used as a conditioning agent in shampoos, hair conditioners, and skin care formulations. The long hydrophobic chain adheres to keratin fibers or skin, while the cationic head reduces static electricity, improves combability, and imparts a soft, smooth feel. Its adsorption to negatively charged surfaces also allows it to function as an antistatic agent and fabric softener in textile applications. In industrial settings, it is utilized in the paper and leather industries as a softening and antistatic additive.

The compound also serves as an effective phase transfer catalyst and emulsifier due to its amphiphilic nature. It facilitates reactions between aqueous and organic phases and stabilizes oil-in-water emulsions. Its long-chain alkyl group contributes to the hydrophobic interaction, while the cationic head ensures affinity for polar surfaces, enabling improved performance in both chemical processes and formulated products.

Environmental considerations are important in the use of octadecyl trimethyl ammonium chloride. As a cationic surfactant, it can be toxic to aquatic organisms and may persist in the environment if wastewater is not properly treated. Safety protocols address occupational exposure, as it can cause skin or eye irritation at higher concentrations. Modern regulations and guidelines ensure its controlled use to mitigate potential ecological impact.

The discovery and industrial development of octadecyl trimethyl ammonium chloride reflect the broader trend in quaternary ammonium chemistry to create surfactants that combine antimicrobial efficacy, surface conditioning, and formulation stability. Its widespread applications in cleaning, personal care, textile, and industrial processes demonstrate the practical value of combining long-chain alkyl groups with quaternary ammonium functionality. Over decades, it has become an essential ingredient in products that require antimicrobial protection, conditioning, and antistatic performance, illustrating the continued importance of quaternary ammonium compounds in modern chemical applications.

References

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2023. Determination of 25 quaternary ammonium compounds in sludge by liquid chromatography�mass spectrometry. Analytical Sciences, 39(5).
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