What Is 2-Mercaptopyridine monoxide

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Last updated: April 15, 2026

Quick Answer: 2-Mercaptopyridine N-oxide is an organosulfur compound with the chemical formula C5H5NOS, used primarily in chemical synthesis and as a reagent in analytical chemistry. It appears as a white to off-white crystalline powder and is valued for its ability to form metal complexes. The compound was first synthesized in the mid-20th century and has since been studied for its unique reactivity.

Key Facts

Chemical formula: C5H5NOS
Molecular weight: 127.17 g/mol
First reported synthesis in 1958
Used in analytical chemistry for metal ion detection
Forms stable complexes with copper and zinc ions

Overview

2-Mercaptopyridine N-oxide is a heterocyclic organosulfur compound that plays a specialized role in chemical research and industrial applications. It is derived from pyridine, with a thiol group at the 2-position and an oxygen atom bonded to the nitrogen, forming an N-oxide. This unique structure gives it distinct reactivity compared to similar thiopyridine derivatives.

The compound is primarily used as a reagent in coordination chemistry and analytical methods due to its ability to chelate metal ions. It is stable under standard storage conditions but should be protected from light and moisture to prevent degradation. Its solubility in polar solvents like ethanol and DMSO makes it suitable for laboratory use.

Chemical formula: The compound has the molecular formula C5H5NOS, consisting of five carbon atoms, five hydrogen atoms, one nitrogen, one oxygen, and one sulfur atom.
Molecular weight: It has a molar mass of 127.17 g/mol, which is important for stoichiometric calculations in synthesis and analysis.
Synthesis date: First prepared in 1958 by oxidation of 2-mercaptopyridine using hydrogen peroxide or peracetic acid.
Physical form: Typically appears as a white to off-white crystalline powder, which may yellow over time if exposed to air or light.
Solubility: Moderately soluble in water but highly soluble in ethanol, methanol, and DMSO, facilitating its use in various reaction media.

How It Works

The functionality of 2-mercaptopyridine N-oxide stems from its dual ability to act as a ligand and a nucleophile, making it valuable in metal coordination and organic transformations. Its structure allows for selective interactions with transition metals, particularly soft metals like copper and zinc.

Ligand behavior: The sulfur and N-oxide oxygen atoms serve as donor sites, enabling the formation of five-membered chelate rings with metal ions.
Coordination with copper: Forms a stable 1:1 complex with Cu(II), useful in analytical detection methods for trace metal analysis.
pKa value: The thiol group has a pKa around 6.5, allowing deprotonation under mild basic conditions to enhance metal binding.
Reactivity in synthesis: Used as an intermediate in the preparation of pharmaceuticals and agrochemicals due to its versatile functional groups.
Stability: More stable than its non-oxidized counterpart, 2-mercaptopyridine, because the N-oxide group reduces oxidative dimerization via disulfide formation.
Environmental sensitivity: Degrades slowly in sunlight; thus, storage in amber glass containers under inert atmosphere is recommended.

Comparison at a Glance

Below is a comparison of 2-mercaptopyridine N-oxide with related compounds in terms of structure and function:

Compound	Molecular Weight (g/mol)	Metal Binding Ability	Primary Use
2-Mercaptopyridine N-oxide	127.17	High (Cu, Zn)	Chemical reagent, metal detection
2-Mercaptopyridine	111.16	Moderate	Corrosion inhibitor
2-Pyridinethiol	111.16	Low to moderate	Organic synthesis intermediate
Thiourea	76.12	Moderate (soft metals)	Photographic developer
EDTA	292.24	Very high (broad spectrum)	Chelating agent in detergents

This table highlights how 2-mercaptopyridine N-oxide balances moderate molecular weight with strong selectivity for specific metal ions. Unlike EDTA, it does not bind all metals indiscriminately, making it more suitable for targeted analytical applications. Its enhanced stability over non-oxidized thiopyridines improves shelf life and reliability in repeated laboratory use.

Why It Matters

Understanding 2-mercaptopyridine N-oxide is essential for researchers in analytical chemistry, materials science, and pharmaceutical development. Its selective metal-binding properties offer advantages in sensor design and environmental monitoring.

Environmental monitoring: Used in test kits to detect copper contamination in water supplies at concentrations as low as 0.1 ppm.
Pharmaceutical intermediates: Serves as a building block in synthesizing compounds with antimicrobial activity.
Corrosion inhibition: Derivatives are studied for protecting copper-based alloys in industrial cooling systems.
Research applications: Enables the study of metalloenzyme mimics due to its biomimetic coordination behavior.
Safety profile: Low acute toxicity but requires handling with gloves and eye protection due to potential skin sensitization.
Commercial availability: Offered by major chemical suppliers like Sigma-Aldrich and TCI, typically at 97% purity and priced around $50–100 per gram.

As analytical techniques advance, the role of specialized reagents like 2-mercaptopyridine N-oxide continues to grow. Its unique combination of stability, reactivity, and selectivity ensures ongoing relevance in both academic and industrial laboratories.