UN/NA Number Reference
DOT Class 6.1 Toxic Substance placard

UN 2521: Diketene, stabilized

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 2521 is assigned the proper shipping name Diketene, stabilized in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 6.1 Toxic Substance material, Packing Group I. Required label(s): 6.1, 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 131)

Hazards: HIGHLY FLAMMABLE. TOXIC. May be fatal if inhaled, swallowed, or absorbed through skin. Vapors heavier than air.

Fire: Small: dry chemical, CO2, water spray, alcohol-resistant foam. Large: water spray, fog, alcohol-resistant foam.

Spill: Eliminate ignition sources. Do not touch. Stop leak if safe. Use vapor-suppressing foam. Ventilate area.

Chemical and Physical Properties

Diketene, stabilized appears as a colorless liquid with a disagreeable odor. Slightly less dense than water. Irritates skin and eyes. Used to make paints and pharmaceuticals.

CAS Number: 674-82-8
Molecular Formula: C4H4O2
Molecular Weight: 84.07 g/mol
Color / Form: Colorless liquid; turns brownish-yellow upon standing at room temperature
Odor: Pungent odor
Boiling Point: 261 F
Melting Point: -6.5 °C
Flash Point: 93 F
Autoignition: 590 °F (310 °C)
Specific Gravity: 1.0877
Vapor Pressure: 10.7 mmHg
Vapor Density: 2.9 (heavier than air)
Water Solubility: Decomposes in water

Special Provisions

49 CFR 172.102 special provision codes for this entry: 2, 387, B9, B14, B32, T20, TP2, TP13, TP38, TP45. 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 2521 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.