What Is 2-Mercaptopyridine N-oxide

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Last updated: April 15, 2026

Quick Answer: 2-Mercaptopyridine N-oxide (C5H5NOS) is an organosulfur compound with a molecular weight of 127.17 g/mol, first synthesized in 1956. It is primarily used as a fungicide and antimicrobial agent in industrial and cosmetic applications.

Key Facts

Molecular formula: C5H5NOS
First synthesized in 1956 by researchers at Hoffmann-La Roche
Used in anti-dandruff shampoos at concentrations up to 0.5%
Exhibits antifungal activity against Malassezia species
Boiling point: 285°C under standard atmospheric pressure

Overview

2-Mercaptopyridine N-oxide is a heterocyclic organic compound derived from pyridine, featuring both sulfur and oxygen functional groups. It appears as a white to off-white crystalline powder and is known for its stability under a range of pH conditions, making it suitable for diverse formulations.

The compound is widely recognized for its biocidal properties, particularly in controlling fungal and bacterial growth. Due to its low toxicity profile in humans at regulated concentrations, it has gained approval for use in consumer products such as shampoos and industrial preservatives.

Chemical structure: Contains a pyridine ring with a thiol (-SH) group at the 2-position and an N-oxide functional group, contributing to its reactivity and solubility in polar solvents.
Molecular weight: Precisely 127.17 g/mol, allowing for accurate dosing in pharmaceutical and industrial applications where precision is critical.
Solubility: Moderately soluble in water (4.2 g/L at 25°C), enhancing its utility in aqueous-based products like lotions and cleaning agents.
Synthesis date: First prepared in 1956 by chemists at Hoffmann-La Roche during research into antimicrobial heterocycles, marking a milestone in antifungal chemistry.
Regulatory status: Approved by the U.S. FDA for use in over-the-counter anti-dandruff shampoos at concentrations not exceeding 0.5% by weight.

How It Works

The antimicrobial activity of 2-mercaptopyridine N-oxide stems from its ability to disrupt microbial cell membranes and interfere with essential enzyme systems. Its dual functional groups enhance penetration and binding to metal ions in microbial proteins, leading to cellular dysfunction.

Mechanism of action:Binds to metal ions in fungal enzymes, particularly zinc-dependent proteases, inhibiting their function and leading to cell death in pathogens like Malassezia furfur.
Antifungal spectrum: Effective against dermatophytes and yeast species at concentrations as low as 8–16 µg/mL in vitro, making it potent even in trace amounts.
pH stability: Remains active between pH 4.0 and 8.0, allowing compatibility with a wide range of cosmetic and industrial formulations without degradation.
Derivatives: The sodium salt form, 2-mercaptopyridine N-oxide sodium, is more water-soluble and commonly used in liquid disinfectants and sanitizers.
Decomposition: Begins to degrade at temperatures above 250°C, releasing sulfur dioxide, which necessitates careful storage below 40°C in sealed containers.
Environmental impact: Shows low bioaccumulation potential with a log P value of 0.89, indicating moderate hydrophilicity and reduced risk to aquatic ecosystems.

Comparison at a Glance

The following table compares 2-mercaptopyridine N-oxide with similar antimicrobial agents in terms of chemical and functional properties:

Compound	Molecular Weight (g/mol)	Primary Use	Effective Concentration	Regulatory Approval
2-Mercaptopyridine N-oxide	127.17	Antifungal in cosmetics	0.1–0.5%	FDA OTC Monograph
Ketoconazole	425.88	Prescription antifungal	1–2%	FDA-approved
Clotrimazole	344.4	Topical antifungal	1%	FDA-approved
Zinc pyrithione	238.7	Dandruff control	0.5–1%	FDA OTC Monograph
Terbinafine	273.44	Oral/dermal antifungal	0.5–1%	FDA-approved

This comparison highlights that 2-mercaptopyridine N-oxide is among the lightest molecules in its class and operates effectively at lower concentrations than many prescription alternatives. Its inclusion in OTC products reflects its safety and efficacy profile, especially in long-term use scenarios such as scalp treatments.

Why It Matters

Understanding the role of 2-mercaptopyridine N-oxide is essential for developing safer, more effective antimicrobial solutions in both consumer and industrial markets. Its targeted action and regulatory acceptance make it a model compound for sustainable biocide design.

Consumer health: Helps reduce dandruff and seborrheic dermatitis in millions of users, improving quality of life and scalp hygiene with minimal side effects.
Industrial use: Incorporated into paints, adhesives, and textiles to prevent mold growth, extending product lifespan by up to 30% in humid environments.
Cost efficiency: Requires only small quantities for efficacy, reducing raw material costs and making it economically viable for mass-market products.
Alternative to antibiotics: Offers a non-antibiotic option for microbial control, helping reduce the risk of antimicrobial resistance in public health settings.
Formulation flexibility: Compatible with surfactants and polymers in shampoos and lotions, enabling stable, long-shelf-life products without refrigeration.
Global availability: Manufactured in China, Germany, and the USA, ensuring consistent supply chains for international cosmetic and pharmaceutical industries.

As demand grows for effective yet safe antimicrobials, 2-mercaptopyridine N-oxide remains a key player in bridging performance and safety, particularly in non-prescription products where consumer access and trust are paramount.