These materials usually have low vapor pressures and are non-flammable. All are combustible. They evolve poisonous gases such as HCN, NOx, SOx, and CO when they burn.

Isocyanates and thioisocyanates are incompatible with many classes of compounds, reacting exothermically to release toxic gases. Reactions with amines, aldehydes, alcohols, alkali metals, ketones, mercaptans, strong oxidizers, hydrides, phenols, and peroxides can cause vigorous releases of heat. Acids and bases initiate polymerization reactions in these materials. Some isocyanates react with water to form amines and liberate carbon dioxide. Polyurethanes are formed by the condensation reaction of diisocyanates with, for example, ethylene glycol.

Upon direct exposure, members of this chemical class are toxic. Vapors irritate mucous membranes. Organic isocyanates and isothiocyanates are known sensitizers for a small percentage of people, causing chemically induced allergic reactions. The effects of these reactions can be dramatic at rather low concentrations.

Compounds in this group have the general formulas R-N=C=O and R=N=C=S where R represents an organic group. Isocyanates are isomers of cyanates, which have the general formula R-O=C=N. No organic cyanates exist in the monomeric state. They immediately trimerize to alkyl cyanurates, which are also in this reactivity group.

Phenylene diisocyanate, cyclohexane diisocyanate, naphthalene diisocyanate, cyclohexyl isocyanate, ethyl isocyanate, isobutyl isocyanate, isopropyl isocyanate, methyl isocyanate, n-butyl isocyanate, phenyl isocyanate, propyl isocyanate.