1 Classification reactions Isocyanates

There are several areas of uncertainty regarding the literature classification of phosgene chemistry. The most common classification is based on the nature of the reaction center and usually lists the reagents, or the products of reaction (isocyanates, carbonates, carbamates, ureas, chloroformates, acid chlorides, isonitrUes, nitriles, carbodiimides, etc.) [1, 2]. 

Agawa and his co-workers have reported a series of investigations of the reactions of cumulenes with oxaziridines. Reaction with isocyanates led to oxadiazolidinones 86 45,70 same product obtained from nitrones and isocyanates. Detailed mechanistic information is not available and the classification of these reactions as cyclo-... 

Many authors divide polymerizations into chain reactions and stepwise reactions. Of course, all reactions proceed in steps, that is, one reaction step follows another. Termolecular reactions are rare but in the organic chemistry sense, the term stepwise reaction signifies that intermediate products can be isolated and subsequently again made to react. This means that, in the absence of impurities, certain reactions can be frozen. In actual fact, anionic addition polymerizations can be frozen at low temperatures and made to run again at higher temperatures. That this procedure is not possible in the presence of water or carbon dioxide is an experimental consideration and not a conceptual difficulty. If we lived in an isocyanate atmosphere, no steps could be isolated in the polyamide synthesis. Thus, such classifications are based on experimental expertise, which can never be the basis of a physical definition. 

Phosgene is manufactured from a reaction of carbon monoxide and chlorine gas in the presence of activated charcoal. Phosgene is used in the manufacture of isocyanates, polycarbonates, pesticides, dyes, and pharmaceuticals. Manufacture of phosgene in the United States is almost entirely captive in that more than 99% is used in the manufacture of other chemicals within a plant boundary (US EPA, 2003). The odor threshold is between 0.5 and 1.5 ppm (NIOSH, 1976) unfortunately, the odor threshold is inadequate to protect against toxic inhalant exposure because damage to the deep respiratory tract can take place at lower concentrations (Sidell et al., 1997). Phosgene has an odor safety classification rating of "E," which indicates that fewer than 10% of attentive persons can detect the Threshold Limit Value (TLV) (Amoore and Hautala, 1983). 

---