Isocyanates

Abstract

Isocyanates are a group of reactive, low molecular weight aromatic, and aliphatic compounds containing the isocyanate group (–NCO). Organic compounds that contain one isocyanate group are termed isocyanates. Isocyanates that contain two isocyanate groups are known as a diisocyanates. The isocyanate functional group is unsaturated and readily reacts with compounds containing active hydrogen atoms. Hence, diisocyanates readily react with water whether in liquid or mist form, alcohols, amines, etc. In addition, diisocyanates also react with themselves to form either dimers or trimers. Diisocyanates that react with alcohol, form carbamates (NHCOO–). Isocyanates are used in the manufacture of foams, fibers, paint coatings, elastomers, and insulation applications. Occupational exposures to isocyanates are generally related to the vapor pressures of the individual compounds. Lower molecular weight isocyanates will volatilize at room temperature, creating a vapor inhalation hazard. On the other hand, higher molecular weight isocyanates do not readily volatilize at ambient temperatures; however, present a hazard if heated or aerosolized. Isocyanates are skin, eye, respiratory, and gastrointestinal irritants. They are also powerful sensitizers that have caused severe asthma, which has been fatal in some instances. Isocyanates can also cause contact dermatitis (both irritant and allergic forms) and hypersensitivity pneumonitis. Isocyanate-induced asthma in occupationally exposed populations vary from 5% in diisocyanate production facilities to up to 30% in polyurethane production facilities. The most widely used isocyanates are diisocyanates and polyisocyanates, which contain more than two isocyanate groups. The most commonly known isocyanates such as methylene diphenyl diisocyanate; CASRN: 26447-40-5, methyl isocyanate; CASRN: 624-83-9, hexamethylene diisocyanate; CASRN: 822-06-0, toluene diisocyanate; CASRN: 26471-62-5, naphthalene diisocyanate; CASRN: 3171-72-6, isophorone diisocyante; CASRN: 4098-71-9, Methylene bis-cyclohexylisocyante; CASRN: 5124-30-1 are all covered in this article. However, the following isocyanates are also covered in more detail elsewhere in this book: methylene diphenyl diisocyanate, CASRN: 26447-40-5 (see 01211); methyl isocyanate, CASRN: 624-83-9 (see 00333); and hexamethylene diisocyanate, CASRN: 822-06-0 (see 01131).