Methyl isocyanate production

The initial Indian managerial and supervisory staff for the Bhopal methyl isocyanate production unit was trained in Union Carbide s West Virginia plant. As prospects declined and the future of the Bhopal facility became doubtful, the trained staff began leaving for more attractive jobs and were replaced by employees who had not received prior training in operating an MIC plant. Additionally, low production volumes seemed to justify workforce... 

Naphthol is mainly used in the manufacture of the insecticide carbaryl (59), l-naphthyl A/-methyicarbamate/ iJ-2j5 - (Sevin) (22), which is produced by the reaction of 1-naphthol with methyl isocyanate. Methyl isocyanate is usually prepared by treating methylamine with phosgene. Methyl isocyanate is a very toxic Hquid, boiling at 38°C, and should not be stored for long periods of time (Bhopal accident, India). India has developed a process for the preparation of aryl esters of A/-alkyl carbamic acids. Thus l-naphthyl methylcarbamate is prepared by refluxing 1-naphthol with ethyl methylcarbamate and POCl in toluene (60). In 1992, carbaryl production totaled > 11.4 x 10 t(35). Rhc ne-Poulenc, at its Institute, W. Va., facihty is the only carbaryl producer in United States. 

A similar product is obtained from the reaction of anhydro-4(5)-hydroxy-l,2,3-triazolium hydroxide (398). In this case reaction with DMAD occurred in 1 hour in boiling benzene. Extrusion of methyl isocyanate from the initial 1 1 cycloadduct (399) occurred during the reaction giving (400). 

Substitution If intensification is not possible, then an alternative is to consider using a safer material in place of a hazardous one. Thus it may be possible to replace flammaole solvents, refrigerants, and heat-transfer media by nonflammable or less flammable (high-boiling) ones, hazardous products by safer ones, and processes which use hazardous raw materials or intermediates by processes which do not. As an example of the latter, the product manufactured at Bhopal (carbatyl) was made from three raw materials. Methyl isocyanate is formed as an intermediate. It is possible to react the same raw materials in a different order so that a different and less hazardous intermediate is formed. 

A simple and efficient method of production of A-methyl ureas, which avoids the use of methyl isocyanate, has been applied to 5//-dibenz[6,/]azepine (5)- 16.ios... 

The study of the accidents in chemical facilities, during transportation, storage and others, the research of the chemical products, which are produced and stored, are important points in the preparation of the defence against chemical terrorism. An example of such an accident is the explosion at the Union Carbide pesticide manufacturing plant (Dec. 3, 1984), which scattered toxic methyl isocyanate (MIC) over the city of Bhopal, India. During the first few days up to 4000 people died of painful, harrowing deaths [10],... 

Key steps, as shown in Scheme 4-15, involve the formation of a urethane intermediate 37 by treating epoxide 36 with methyl isocyanate in the presence of sodium hydride. Intramolecular A-nucleophilic ring opening of oxirane affords oxazolidine 38. Subsequent treatment furnishes product 34. 

To this end, the diazoimidazole carboxamide compound 32 was transformed first by methylamine to the methyl-triazene derivative 39, which was reacted with 11 (". -phosgene to give the desired product 40 <2002JME5448>. In another approach, 32 was directly cyclized to the bicyclic product by using 1 C-labeled methyl isocyanate. This route allowed the synthesis of both the C-2-labeled 40 and the (7-methyl-labeled samples 41 <1997JLR371, 2002JME5448> (Scheme 13). 

Isopropanolamines, 20 795, 812 2-Isopropanol-water system, evolving separation strategies for, 22 322-325. See also Water- IPA-hexane system Isopropenyl acetate, 7 148 74 596 m-Isopropenyl-a,a-dimethylbenzyl isocyanate (TMI), 25 463 Isopropenyl methyl ether, production from acetone, 7 163... 

The structures of lithium and sodium cyanates and isocyanates and their related ion-pair 5n2 reactions have been examined by using quantum mechanics at the Hartree-Fock (HF)/6-31G V/HF/6-31G level. (The cyanate ion is NCO the isocyanate ion is CNO. ) The isocyanate ion pairs are the most stable monomeric forms the lowest energy dimers are planar eight-membered rings. For the ionic 5 n2 reaction of cyanate ion with MeF or MeCl, methyl isocyanate is the predicted major product. Predictions about the 5ivr2 reactions of the ion pairs were also made. 

Photolytic. Based on data for phenol, a structurally related compound, an aqueous solution containing 1-naphthoxide ion (3 x 10 M) in room light would be expected to photooxidize to give 2-hydroxy-1,4-naphthoquinone (Tomkiewicz et al., 1971). 1-Naphthol, methyl isocyanate, and other unidentified cholinesterase inhibitors were reported as products formed from the direct photolysis of carbaryl by sunlight (Wolfe et al., 1976). In an aqueous solution at 25 °C, the photolysis half-life of carbaryl by natural sunlight or UV light (X = 313 nm) is 6.6 d (Wolfe et al, 1978a). 

Nitrogen-15 NMR has been used to study the course of acylation and carbamidization reactions of 3-amino-5-methylthio-1,2,4-thiadiazole (3). Using a N label in the 2-position of (3), its reaction with hard nucleophiles was found to proceed via initial reactioa on the 2-position followed by a Dimroth rearrangement to give the acylated product (4) with the N label in the exocyclic position. The reaction of (3) with soft nucleophiles, such as methyl isocyanate occurs directly on the exocyclic nitrogen to give the urea (5) (Scheme 1) <84CHEC-l(6)463 >. 

In an examination of the reactions of a-ureido nitrogen heterocycles with chlorothioformyl chloride it was found that (607) reacted to give (608) in yields of 12-63% depending on the nature of R. The products were rather unstable and decomposed with loss of methyl isocyanate and sulfur both on heating and on long standing at room temperature (73JOC1578). 

Methyl isocyanate (1.14 g, 20 mmol) was dissolved in 70% HF/pyridine (20 mL) in a polyethylene bottle at 0 C. The mixture was then stirred at rt for 24 h and extracted with CHC1, the CHC13 was then carefully removed by distillation on a rotary evaporator. The residue was distilled under reduced pressure yield 0.6 g (40%) bp 48 50 C/6 Torr the product was characterized by H NMR and IR spectroscopy. 

The biocidal activity of the thiadiazine (12) is probably related to the production of methyl isocyanate inside the cell by hydrolysis (equation 7). Isocyanates are known to have fungicidal properties (B-69MH1502), thought to be due to their reaction with sulfhydryl groups to form dithiocarbamates. The formation of these last mentioned compounds, by ring cleavage, might also explain the activity of 2-mercaptobenzothiazole (16). 

In the gas-phase thermolysis of 44, only the products of cycloreversion are observed (97JHC113).The unsymmetrically substituted compounds 44c and 44d seem to decompose by the two alternative ways, because both iso-cyanic and hydrazoic acid are detected simultaneously. However, from the complementary products only ethyl and phenyl isocyanate, but not the corresponding azides, are found. Compounds 44b and 44f decompose only in one way, affording methyl isocyanate and hydrazoic acid, and phenyl isocyanate and methyl azide, respectively, as the primary reaction products (Scheme 3). 

A typical example of the reaction of isocyanates with formamidines is shown in equation (92). Alkyl isocyanates can react in a similar way, but there can be mixed products formed under certain circumstances, as in the reaction of methyl isocyanate with N,N- dialkyl-N 1-arylformamidines (166). The predicted product (167 equation 93) is formed except when AT,AT-dimethyl-N-arylformamidines are used. In the latter case a mixture of (168) and (169) is formed (equation 94). The mechanism of the formation of (169) is shown in Scheme 104 (73HCA776). 

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 (MIC), the material that was released at Bhopal, can be produced and immediately converted to final product in a process that contains a total inventory of less than 10 kg of MIC (6). 

Reaction of methylenephosphinophosphorane 83 with methyl isocyanate afforded zwitterionic compounds 84, 85 in a ratio 7 1 (Scheme 13) <1995TL2021>. However, the reaction is reversible. In nonpolar solvents the equilibrium is shifted to the cyclic products, while dissolving the latter in polar solvents leads to their decomposition to the starting reagents. If sulfur is added to the reaction mixture, compounds 84 and 85 disappear leaving oxidized compound 86 as the only product. Ethyl isocyanate reacts with compound 83 in a similar manner. 

Methanol is oxidized to formaldehyde in a thin layer of finely divided silver or a multilayer screen, with a contact time of 0.01 s at 450 to 600°C (842 to 1112°F). A shallow bed of silver catalyst is also used in the DuPont process for in situ production of methyl isocyanate by reacting monomethlyformamide and oxygen at 500°C. 

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. 

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