Poison by ingestion. A dienophile. Explosive reaction with 1-methylsilacyclopenta-2,4-diene at 150°C. Octakis(trifluorophosphine)dirhodium catalyzes explosive polymerization of the acid above 20°C. When heated to decomposition it emits acrid smoke and irritating fumes. Hazard Codes:?C Risk Statements: 34-22? R34: Causes burns.? R22: Harmful if swallowed. Safety Statements: 23-26-27-36/37/39-45? S23: Do not breathe vapour.? S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.? S27: Take off immediately all contaminated clothing.? S36/37/39: Wear suitable protective clothing, gloves and eye/face protection.? S45: In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) RIDADR: UN 3265 8/PG 2 WGK Germany: 3 RTECS: ES0175000 F: 8-19 HazardClass: 8 PackingGroup? of Dimethyl acetylenedicarboxylate (CAS NO.762-42-5): III