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Isocyanates are the class of organic compounds which contain an isocyanate group (-N=C=O). These compounds are prepared by the reaction of amines with phosgene. Isocyanates are electrophiles and reactive towards various nucleophiles such as alcohols and amines. When reacted with alcohols, isocyanates give urethanes, and when reacted with amines the product formed is urea. If the organic compounds have two isocyanate groups then they are named as diisocyanates. When treated with a compound containing two or more hydroxyl groups such as a diol or a polyol, diisocyanates give polymer chains called polyurethanes. Diisocyanates react with a compound containing two or more amine groups giving long polymer chains known as polyureas. Cyclization occurs when isocyanates react with themselves.
Isocyanates have several applications in organic reactions. In the Diels-Alder reaction, isocyanates act as a dienophile. Hofmann rearrangement, Schmidt reaction, Curtius rearrangement and Lossen rearrangement are some of the transformations which involve in the formation of isocyanate as an intermediate. Methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) are some of the common isocyanates globally marketed for various industrial applications. Methyl isocyanate (MIC) is a monofunctional isocyanate with high industrial significance.