Methyl isocyanate trimerization

Trimerization of methyl isocyanate (MeNCO) in the presence of tri-n-butylphosphine gives a... 

Interestingly, methyl isocyanate is noted to form unusual trimer products in the presence of trialkylphosphine catalysts. Both the expected triazine (19) and 3,5-dimethyl-2-methylimino-4,6-dioxohexahydro-l,3,5-oxadiazine (20) products are formed (62). 

Methyl isocyanate and all isocyanic acid esters are an interesting and highly reactive class of organic compounds, since the isocyanate group (-NC0) reacts readily with a wide variety of compounds as well as with itself to form dimers, trimers, ureas, and carbodi-imides. Methyl isocyanate (MIC) is an intermediate in the preparation of carbamate pesticides and conceivably could be applied to the production of special heterocyclic polymers and derivatives. 

Trimerization of methyl isocyanate (MeNCO) in the presence of tri- -butylphosphine gives a 1,3,5-oxadiazine 736 <1973CRC(277)795>. In the presence of carbon dioxide, the reaction leads to the 1,3,5-oxadiazinimine 737 derived from C02 (1 mol eq.) and the isocyanate (2 mol eq.) <1974BSF1497>. 

Physicochemical Reactions with MIC MIC can interact with a large number of molecules as well as with itself Indeed, 21 identified (Varadarajan et al., 1985) and almost ten unidentified chemicals (Sriramachari, 2004) were detected in the culprit MIC Tank E-610. An MIC trimer as well as other metabolites of MIC such as dimethyl isocyanurate and 2,4-dione of methyl isocyanate were identified in autopsy samples from Bhopal victims (Chandra et al, 1991, 1994 Saraf et al, 1995). Reaction of MIC with water is important because this will occur whenever MIC comes into contact with a body or environment, as happened in Bhopal. It is important to note that while excess water can neutralize MIC, a small quantity of water is sufficient to generate heat during the reaction, which would lead to vaporization of MIC, as actually happened in Bhopal. Some important interactions of MIC are enumerated below ... 

The cyclotrimerization of carbon cumulenes is usually initiated by heat or catalysis. Especially, the use of a catalyst assures that trimerization can be accomplished in quantitative yields. The base catalyzed cyclotrimerization reaction seems to be limited to ketenes, isocyanates, isothiocyanates and carbodiimides. In the trialkylphosphine catalyzed trimerization of methyl isocyanate an asymmetric trimer is obtained. 

The cyclotrimerization reaction of alkyl- and aryl isocyanates to give trisubstituted isocya-nurates (hexahydro-5-triazinetriones) is a well known reaction. Many base and acid catalysts are effective and only highly sterically hindered isocyanates fail to undergo trimerization. In all cases the symmetric trimers 17 are obtained, and only in the trimerization of methyl isocyanate using a trialkylphosphine catalyst is the unsymmetrical trimer 18 isolated as a coproduct... 

A large number of hindered phenoHc antioxidants are based on the Michael addition of 2,6-di-/ f2 -butylphenol and methyl acrylate under basic catalysis to yield the hydrocinnamate which is a basic building block used in the production of octadecyl 3-(3,5-di-/ f2 butyl-4-hydroxyphenyl)propionate, [2082-79-3], tetrakis(methylene-3(3,5-di-/ f2 butyl-4-hydroxylphenyl)propionate)methane [6683-19-8], and many others (63,64). These hindered phenolic antioxidants are the most widely used primary stabilizers in the world and are used in polyolefins, synthetic and natural mbber, styrenics, vinyl polymers, and engineering resins. 2,6-Di-/ f2 -butylphenol is converted to a methylene isocyanate which is trimerized to a triazine derivative... 

---