Urethans and isocyanate

Figures 13.25-13.28 show the ultrahigh resolution separations in chloroform of polystyrene standards, polytetramethylene glycol, urethanes and isocyanates, and epoxy resins, respectively. Multiple column sets of anywhere from two to six columns in series have been used for well over a year with no apparent loss of efficiency. The 500- and 10 -A gels can easily tolerate 15,000 psi or more. In fact, the limiting factor in the number of columns that can be used in series is generally the pump or injector in the FIPLC system. A pump capable of 10,000 psi operation should allow the use of a column bank of 10-12 50-cm columns with a total plate count of 500,000 or more.

Metal-catalyzed reductive carbonylation of nitroaromatics using CO has been the subject of intensive investigation in recent years because of the commercial importance of amines, urethanes, and isocyanates (1). Biphasic operation could offer interesting horizons regarding the ease of catalyst recycling. Thus, palladium catalysts have been applied in the presence of water-soluble ligands such as TPPTS or BINAS (2) for the carbonylation of substituted nitroaromatics (Scheme 1). 

Generation of Urethanes and Isocyanates from Amines and Carbon Dioxide... 

A number of modern industrial processes are based on the catalytic carbonyl at 1 on of organic substrates by carbon monoxide. ll In contrast, the application of carbon monoxide as reductant in organic synthesis is confined to relatively few exampl es. 2l In recent years the catalytic carbonyl at I on of nitro compounds has become a ery intense field of research. This is due to the fact that 3 series of industrially important compounds can be obtained - om nitro compounds and carbon monoxide in a single step azo compounds, amides, amines, oximes, ureas, urethanes and isocyanates [ 3] and indoles. Ureas and urethanes are important final products and intermediates in the synthesis of ert ll eps and pesticides. On the other hand mono and di-1 socyanates are very important intermed 1 a es in the manu-i-acture of pesticides, polyurethane foam plastics, synthetic leather, adhesives and coatings. 

Isocyanate-urethane and isocyanate-urea reactions then yield biurets and allophanates, which produce crosslinking and branching ... 

Urethanes and isocyanates have found widespread use as adhesives, in both industrial and household environments. They can be used to bond a variety of substrates such as rubber, plastics, metals, wood, glass, and ceramics. Polyurethane adhesives display good hydrolytic stability and have... 

This has proven to be a very versatile reaction, which can start with a variety of electrophilic dehydrating agents and organic bases. Furthermore, the mild reaction conditions allow for the use of amine precursors, which can possess a number of different functional groups. Thus the Monsanto activated carbon dioxide process not only eliminates the use of phosgene as a starting material, but also provides additional benefits, including milder reaction conditions, urethane and isocyanate products in quantitative yields, reductions in problem impurities and by-products, and broader possibilities in choice of amine feedstock. 

The Curtius, Hofmann (see p. 267), and Schmidt (see p. 307) reactions are in that order decreasingly mild, decreasingly flexible, and increasingly expeditious. The last-named quality varies somewhat with the available starting material, whether the free acid or the ester. The Curtius reaction lends itself to the preparation of isocyanates, sym-and 08-ureas, amides, urethans, and amines at will, and provides a wide choice of experimental conditions. For synthetic purposes the Hofmann reaction can be used only to prepare sym-ureas, urethans, and amines directly, and halting the reaction at a desired intermediate is often not possible. The variety of experimental conditions is narrower and more limited. The Schmidt reaction on carboxylic acids or derivatives has been applied as a preparative method only to the production of amines although urethans and isocyanates have been prepared occasionally by this reaction, it can hardly be considered a preparative method for them. Amides can be prepared by the Schmidt reaction only from ketones. The choice of experimental conditions employable in the Schmidt reaction is narrow. 

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