Amines phosgene

The above processes are only selected examples of a vast number of process options. In the case of carbonylation, the formation of by-products, primarily isocyanate oligomers, allophanates, and carbodiimides, is difficult to control and is found to greatly reduce the yield of the desired isocyanate. Thus a number of nonphosgene processes have been extensively evaluated in pilot-plant operations, but none have been scaled up to commercial production of diisocyanates primarily due to process economics with respect to the existing amine—phosgene route. Key factors preventing large-scale commercialization include the overall reaction rates and the problems associated with catalyst recovery and recycle. 

Isocyanates may be prepared via a number of routes, including the thermal cracking of urethanes or silylurethanes [107], or the reaction of N-alkylcarbamate esters with boron trichloride [108] or chloroboranes [109] or chorosilanes [110] in the presence of bases (NEt3). To date, however, only amine phosgenation is practiced on a significant industrial scale [10, 106],... 

BROMINE CYANIDE (506-68-3) Able to polymerize. May be unstable unless dry and pure impure material decomposes rapidly and tends to explode. Reacts violently with acids, ammonia, amines, phosgene. Water contact produces hydrogen cyanide and hydrogen bromide. 

An interfacial polymerization procedure is also employed in direct phosgenations. A caustic solution of the diphenol is dispersed in an organic chlorinated solvent containing small quantities of a tertiary amine. Phosgene is bubbled through the reaction mixture at 25 °C. When the reaction is complete, the organic phase contains the polymer. It is separated and the product isolated as above. 

Acetoacetic ester, sec-butyl amine, phosgene, bromine... 

Reactions with Carboxylic Acids, Alcohols, and Amines. Phosgene reacts with carboxylic acids to give anhydrides, with liberation of carbon dioxide. This has been used to activate acids to attack from nucleophiles, e.g. in esterification, lactonization, and thiolation. For example, acids can be protected as 3-butenyl esters using phosgene and Pyridine, followed by addition of 3-buten-l-ol (eq 1). 

With tertiary amines, phosgene-amine complexes can be formed. Warming results in decomposition to an N,N-dialkylchloroformamide by elimination of alkyl chloride. This has been utilized for the mild and high yielding deprotection of A-methyl amines (eq 8). a-Chloroethyl chloroformate, prepared... 

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