UN/NA Number Reference
DOT Class 3 Flammable Liquid placard

UN 2346: Butanedione

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 2346 is assigned the proper shipping name Butanedione in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 3 Flammable Liquid material, Packing Group II. Required label(s): 3.

Packing group indicates the degree of danger within a hazard class: PG I is high danger, PG II medium, PG III low. The proper shipping name, hazard class, UN number, and packing group together form the basic shipping description that must appear on shipping papers and, where required, on the package and placard.

Emergency Response (ERG Guide 127)

Hazards: HIGHLY FLAMMABLE. Vapors may form explosive mixtures with air. Vapors heavier than air, travel to ignition source and flash back. Runoff may cause fire/explosion.

Fire: Small: dry chemical, CO2, water spray or alcohol-resistant foam. Large: water spray, fog or alcohol-resistant foam. Do not use straight streams. Cool tanks with water.

Spill: Eliminate ignition sources. Ground equipment. Stop leak if safe. Use vapor-suppressing foam. Absorb with earth/sand. Dike large spills. Water spray may reduce vapor.

Chemical and Physical Properties

Diacetyl appears as a clear colorless liquid with a strong chlorine-like odor. Flash point 80 °F. Less dense than water. Vapors heavier than air.

CAS Number: 431-03-8
Molecular Formula: C4H6O2
Molecular Weight: 86.09 g/mol
Color / Form: Greenish-yellow liquid
Odor: Quinone odor; vapors have a chlorine-like odor
Boiling Point: 190 F
Melting Point: 27.7 °F (NTP, 1992)
Flash Point: 80 F
Autoignition: 689 °F (NTP, 1992)
Specific Gravity: 0.99 (floats on water)
Vapor Pressure: 56.8 [mmHg]
Vapor Density: 3 (heavier than air)
Water Solubility: greater than or equal to 100 mg/mL at 72 F
Log P: log Kow = -1.34

Special Provisions

49 CFR 172.102 special provision codes for this entry: IB2, T4, TP1. These codes modify the general requirements (packaging, quantity limits, exceptions) for this specific material. Look up each code in 49 CFR 172.102 for the full text.

Need the full interactive record? Open UN 2346 in the SpillNerd lookup tool for the live database entry with placard graphics, GHS pictograms, full segregation tables, and synonym search. For another material, use the UN number and chemical lookup.

Reference data compiled from the DOT Hazardous Materials Table (49 CFR 172.101), the 2024 Emergency Response Guidebook, and public chemical databases (PubChem, NIOSH, EPA). Always verify the correct shipping description against the current regulation and the manufacturer's SDS Section 14 before shipping.