UN/NA Number Reference

UN 2531: Methacrylic acid, stabilized

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 2531 is assigned the proper shipping name Methacrylic acid, stabilized in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 8 Corrosive material, Packing Group II. Required label(s): 8.

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 153)

Hazards: TOXIC. Combustible. Corrosive. Causes burns. Toxic fumes when heated.

Fire: Small: dry chemical, CO2, water spray. Large: water spray, foam.

Spill: Do not touch. Stop leak if safe. Use water spray to reduce vapor.

Chemical and Physical Properties

Methacrylic acid appears as a clear colorless liquid (or low-melting solid) with a pungent odor. Corrosive to metals and tissue. Flash point 170 °F. Melting point 61 °F. May polymerize exothermically if heated or contaminated. If the polymerization takes place inside a container, the container may rupture violently. Less dense than water. Vapors heavier than air. Used to make plastics.

CAS Number: 79-41-4

Molecular Formula: C4H6O2

Molecular Weight: 86.09 g/mol

Color / Form: Clear colorless liquid or colorless crystals

Odor: Acrid, repulsive odor

Boiling Point: 325 F

Melting Point: 61 °F (NTP, 1992)

Flash Point: 170 F

Autoignition: 752 °F (USCG, 1999)

Specific Gravity: 1.015 (sinks in water)

Vapor Pressure: 0.65 mmHg at 68 F

Vapor Density: 2.97 (heavier than air)

Water Solubility: greater than or equal to 100 mg/mL at 63 F

Log P: log Kow = 0.93

Regulatory Data

OSHA PEL

none

NIOSH REL

TWA 20 ppm (70 mg/m 3 ) [skin]

IDLH

Special Provisions

49 CFR 172.102 special provision codes for this entry: 41, 387, IB2, T7, TP1, TP18, TP30. 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 2531 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.