5-Methyl-1H-benzotriazole
[CAS 136-85-6]

Identification

• Classification: Analytical chemistry >> Analytical reagent >> Ion chromatography reagent
• Name: 5-Methyl-1H-benzotriazole
• Molecular Formula: C₇H₇N₃
• Molecular Weight: 133.15
• CAS Registry Number: 136-85-6 (49636-02-4)
• EC Number: 205-265-8
• SMILES: CC1=CC2=NNN=C2C=C1

Properties

• Density: 1.3±0.1 g/cm³ Calc.^*
• Melting point: 80 - 82 °C (Expl.)
• Boiling point: 360.6±11.0 °C 760 mmHg (Calc.)^*, 393.8 - 396.5 °C (Expl.)
• Flash point: 181.5±12.2 °C (Calc.)^*, 182 °C (Expl.)
• Solubility: water 6.0 g/L (25 °C) (Expl.)
• Index of refraction: 1.68 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H302-H314-H315-H318-H319-H335
• Safety Statements: P260-P261-P264-P264+P265-P270-P271-P280-P301+P317-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P351+P338-P305+P354+P338-P316-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P363-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Serious eye damage	Eye Dam.	1	H318
Skin corrosion	Skin Corr.	1B	H314
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332

chemBlink Chemical Story

5-Methyl-1H-benzotriazole, CAS 136-85-6, is a methyl-substituted benzotriazole commonly associated with the broader family of tolutriazoles. PubChem identifies it as C7H7N3 and records corrosion-inhibitor use. Its importance comes from the fused benzene-triazole system: several nitrogen atoms can interact with metal surfaces, while the aromatic ring and methyl substituent modify adsorption and hydrophobic character.

Benzotriazoles became important because copper and copper alloys are useful but readily undergo surface oxidation and corrosion in aqueous systems. Adsorbed benzotriazole species can form a protective interfacial layer on copper. Methylbenzotriazole derivatives follow the same general design principle. Rather than acting as a thick coating, relatively small molecules organize at the metal-solution boundary and reduce access of corrosive species to reactive surface sites. This is why tolutriazoles appear in corrosion-control formulations, including cooling-water and metal-protection systems.

The chemistry is strongly interfacial. Nitrogen-rich triazole functionality provides affinity for metal, while the fused aromatic framework helps create a comparatively compact adsorbed layer. Adding a methyl group changes solubility and surface behavior without removing the metal-binding triazole motif. Commercial "tolyltriazole" may also refer to methylbenzotriazole isomer mixtures, so a defined CAS entry such as 136-85-6 should not automatically be treated as identical to every commercial tolutriazole composition.

There is an environmental side to the same chemical stability that makes these inhibitors useful. Benzotriazoles can enter wastewater from industrial and consumer uses, and PubChem/MeSH also recognizes 5-methylbenzotriazole as an environmental contaminant. Persistence is therefore a practical consideration when inhibitors are used in open or discharge-producing systems.

This compound is a useful example of corrosion chemistry being controlled by molecules only a few atoms thick. The protective effect begins not with bulk material strength but with adsorption: a nitrogen-rich heterocycle recognizes a metal surface, assembles at that boundary, and changes the electrochemical environment where corrosion would otherwise proceed.

References:
1. PubChem, 5-Methyl-1H-benzotriazole, CID 8705, CAS 136-85-6.
2. NIST Chemistry WebBook, 1H-Benzotriazole, 5-methyl-, CAS 136-85-6.
3. Finšgar M, Milošev I. Inhibition of copper corrosion by 1,2,3-benzotriazole: a review. Corros Sci. 2010;52:2737-2749.

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