Isocyanate

Isocyanates are a family of organic compounds that contain the N=C=O functional group. The characteristic feature is a reactive N=C=O moiety, typically attached to a hydrocarbon substituent. Isocyanates can be monomeric or part of polymers known as polyisocyanates. They are widely used as building blocks in polyurethane chemistry because they react with compounds containing active hydrogen, such as alcohols and amines, to form urethane or urea linkages.

Commercially important isocyanates include aromatic di- and polyisocyanates such as toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), and hexamethylene diisocyanate (HDI); and aliphatic diisocyanates such as isophorone diisocyanate (IPDI). These monomers are multifunctional, enabling crosslinking and polymer formation for foams, coatings, adhesives and elastomers.

Preparation and properties: Most isocyanates are prepared by phosgenation of amines or related routes. They are typically moisture-sensitive and react with water to release carbon dioxide and amines, and they react with alcohols to form urethanes. Handling requires dry storage and adequate ventilation; inhalation and skin contact can cause irritation and sensitization, with occupational asthma being a major concern.

Safety and environmental aspects: Isocyanates can be irritants and potent respiratory sensitizers. Exposure limits are established by occupational safety agencies, and proper ventilation, containment, and personal protective equipment are recommended to minimize health risks. In the environment, they hydrolyze in water to amines and carbon dioxide, and are generally not persistent in aqueous systems.