1-hydroksybenzotriazol

1-Hydroxybenzotriazole 
Other Names: HOBt, 1-Hydroxy-1H-benzotriazole, N-Hydroxybenzotriazole
CAS Number: 123333-53-9 (wetted with ≥20% water)
Sum Formula: C₆H₅N₃O
Molar Mass: 135.13 g/mol (anhydrous)
Appearance: White to pale beige crystalline powder, wetted with water

1-Hydroxybenzotriazole is a nitrogen-containing heterocyclic compound widely used in peptide synthesis and organic chemistry as a coupling additive to enhance reactivity and suppress racemization. This version is wetted with ≥20% water to reduce explosion risk. It must be handled with caution due to its reactive nature and potential explosive hazard if dry.

Chemical and Physical Properties
Density: ~1.55 g/cm³
Melting Point: Decomposes before melting
Solubility in Water: Slightly soluble
Solubility in Organic Solvents: Soluble in polar organic solvents (e.g., DMF, DMSO, ethanol)
Form: Wetted solid
Odor: Odorless
Stability: Stable when wetted; dry material is sensitive to friction, heat, and shock

Applications
Used as an additive in carbodiimide-mediated coupling reactions (e.g., EDC/HOBt systems)
Improves yields and reduces racemization in amide and peptide bond formation
Used in esterification and acylation reactions
Common in R&D for optimization of synthetic procedures in technical chemistry

Label Elements

Signal Word: Danger

Hazard Statements:

• H207: Fire or projection hazard; increased risk of explosion if desensitizing agent is reduced

• H319: Causes serious eye irritation

• H412: Harmful to aquatic life with long lasting effects

Precautionary Statements:

• P210: Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking

• P212: Avoid heating under confinement or reduction of the desensitizing agent

• P230: Keep wetted with water

• P233: Keep container tightly closed

• P280: Wear protective gloves, protective clothing, eye protection, face protection

• P370 + P380 + P375: In case of fire: Evacuate area. Fight fire remotely due to the risk of explosion

• P501: Dispose of contents/container to an approved waste disposal plant

First Aid Measures
Eye Contact: Rinse cautiously with water for several minutes. Remove contact lenses if present. Seek medical attention
Skin Contact: Wash thoroughly with soap and water. Remove contaminated clothing
Inhalation: Move to fresh air. Get medical advice if symptoms occur
Ingestion: Rinse mouth. Do not induce vomiting. Seek medical assistance

Handling and Storage
Store in a tightly closed container in a cool, dry, and well-ventilated area
Keep material wetted with water at all times to minimize explosive hazard
Avoid sources of ignition, shock, friction, or mechanical impact
Use non-sparking tools and appropriate PPE