A derivative of isocyanic acid. Isocyanates are represented by the general formula R–N=C=O, where R is predominantly alkyl or aryl; however, stable isocyanates in which the N=C=O group is linked to elements such as sulfur, silicon, phosphorus, nitrogen, or the halogens have also been prepared. Most members of this class of compounds are liquids that are sensitive to hydrolysis and are strong lacrimators. Isocyanates are extremely reactive, especially toward substrates containing active hydrogen. They have found wide use in the commercial manufacture of polyurethanes, which are used in making rigid and flexible foam, elastomers, coatings, and adhesives.