Monoisocyanates

Monoisocyanates, or monoisocyanates, are a class of organic compounds characterized by a single isocyanate functional group (-N=C=O) per molecule. They are the mono-functional counterparts to di- and polyisocyanates used in polymer chemistry.

Structure and examples: The general formula is R-NCO, where R can be an alkyl, aryl, or other substituent. Common simple monoisocyanates include methyl isocyanate (MIC, CH3-NCO) and phenyl isocyanate (Ph-NCO). A variety of monoisocyanates derived from aliphatic or aromatic amines or alcohols exist and are used as intermediates in synthesis.

Production: Monoisocyanates are typically prepared from corresponding amines by phosgenation or by routes such as the Curtius rearrangement of azido compounds; they may also be formed by dehydration of carbamates. Handling requires dry conditions due to moisture sensitivity.

Reactions and uses: The NCO group reacts with nucleophiles including alcohols to give urethanes, with amines to give ureas, and with water to release amines and carbon dioxide. As mono-functional reagents, they can terminate polymer chains or serve as end-cappers, enabling synthesis of defined low- to moderate-molecular-weight products, urethane resins, or as intermediates in agrochemical or pharmaceutical synthesis.

Safety: Isocyanates are typically hazardous; methyl isocyanate in particular is highly toxic and a respiratory sensitizer. They are moisture sensitive and should be handled under appropriate containment with suitable ventilation, protective equipment, and storage away from moisture.