Isocyanates, addition compounds

The /i-iodoisocyanate obtained by addition of iodine isocyanate to alkenes can be transformed into aziridines via carbamates, amine salts, or bisulfite addition compounds <67JOC540>. 

Isocyanates are very reactive toward compounds containing labile hydrogen atoms, forming addition compounds with the hydrogen donors. One such reaction, with hydroxyl-bearing compounds to form carbamates, or urethanes,... 

There are a number of syntheses leading to the formation of urethane polymers. However, the most important commercial route is the isocyanate addition polymerization, the reaction between di- and polyfunctional hydroxyl compounds such as hydroxy-terminated polyethers or polyesters and di- or polyisocyanates. When difunctional reactants are being used, linear polyurethanes are produced and the reaction can be schematically represented as follows ... 

But the most commercially important polyreaction in isocyanates is their addition onto compounds of the general type XH, where X, for example, is OH, OR, SR, NHR, NR2, PH, SiH, RCOO, Hal, etc. In the German-speaking region, this type of polyreaction is known as polyaddition to distinguish it from addition polymerization and condensation polymerization. This polyreaction is mechanistically a polycondensation without elimination of a small molecule in the case of isocyanate addition to hydroxyl groups,... 

Isocyanates form addition products reversibly with compounds which contain moderately reactive hydrogen, such as phenol, oximes, lactams and malonates. Fig. 14 is an example of a typical blocking-unblocking reaction. These addition compounds, called blocked isocyanates, are stable to water. They have been used in place of free isocyanate. The phenol-blocked isocyanates are the most common. In 1957 the DuPont Co. developed an aqueous dip based on blocked isocyanate. This process, called D-417, used phenol-blocked methylene bis(4-phenyl isocyanate) and a water soluble epoxide, the reaction product of glycerine and epichlorohydrin. RFL is used as the topcoat or second step dip ... 

Curing reactions in the case of polyurethanes can be divided into two main classes (a) the reaction of isocyanates with compounds containing reactive hydrogen atoms to give addition products and (b) the polymerization of isocyanates, le, self-addition. 

Both aliphatic and aromatic isocyanates can be blocked by a variety of blocking agents. These include alcohols, phenols, oximes, lactams, j8-dicarbonyl compounds, bisulfite addition compounds, hydroxylamines and esters of p-hydroxybenzoic acid and salicylic acid. Perhaps the most widely used blocking agents at present are phenol, branched alcohols, 2-butanone oxime (methyl ethyl ketoxime) and 8-caprolactam. The use of blocked isocyanates in PU coatings has been comprehensively reviewed. ... 

Benzisothiazolinone (54 R = H) dissolves in aqueous sodium bisulphite to yield, instead of the expected Bunte salt (55 R = SOaNa), an addition-compound of structure (56 R = SOgNa). Cyanide ion reacts similarly to give (56 R = CN). In spite of the acidity of its NH group (54 R = H) reacts with phenyl isocyanate and sodium cyanate to yield the ureido-derivatives (54 R = CONHPh and CONHa). ... 

Hydroxyl groups have also been introduced into SKI 3, which gave a modest increase in green strength, but required addition of an isocyanate in the compound to give a large effect. Inferior tensile, tear and dynamic properties of the isocyanate-treated compound resulted and it is likely that processing problems would be encountered. 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Synthesis from OC-Amino Acids and Related Compounds. Addition of cyanates, isocyanates, and uiea derivatives to a-amino acids yields hydantoin piecuisois. This method is called the Read synthesis (2), and can be considered as the reverse of hydantoin hydrolysis. Thus the reaction of a-amino acids with alkaline cyanates affords hydantoic acids, which cyclize to hydantoins in an acidic medium. 

Addition Polymers. The most commonly referenced reaction of isocyanates iavolves their addition to polyhydroxyl, polyamine, or polycarboxyhc acid compounds to yield addition polymers. Due to the wide diversity of raw material characteristics and the broad range of functionahty, polyurethane polymers having a wide range of processiag and performance characteristics are available. 

Since 1971, the overall demand for isocyanates has increased at a compounded rate of 12%. Although this level will not likely be sustained in the future due to the maturation of key appHcation markets, it is probable that additional growth will occur through the year 2000. This trend will likely iaclude a shift in emphasis from TDl to MDl and polymeric MDl-based materials. New growth opportunities in the constmction industry, stmctural appHcations, and growth in the automotive industry exist. Third-world markets are also anticipated to provide growth opportunities. 

Because of their relative instabiUty, primary phosphine oxides caimot be isolated and must be converted direcdy to derivatives. Primary and secondary phosphine oxides undergo reactions characteristic of the presence of P—H bonds, eg, the base-cataly2ed nucleophilic addition to unsaturated compounds such as olefins, ketones, and isocyanates (95). 

Methylarsine, trifluoromethylarsine, and bis(trifluoromethyl)arsine [371-74-4] C2HAsF, are gases at room temperature all other primary and secondary arsines are liquids or solids. These compounds are extremely sensitive to oxygen, and ia some cases are spontaneously inflammable ia air (45). They readily undergo addition reactions with alkenes (51), alkynes (52), aldehydes (qv) (53), ketones (qv) (54), isocyanates (55), and a2o compounds (56). They also react with diborane (43) and a variety of other Lewis acids. Alkyl haUdes react with primary and secondary arsiaes to yield quaternary arsenic compounds (57). 

Although the first polyurethanes were similar to that shown above, several polymers currently used contain many linkages in addition to the urethane group. Because of this the term polyurethane is now generally extended to cover all the complex reaction products of isocyanates and polyhydroxy compounds (the latter frequently known in this context as polyols). 

In some cases it may be desired to increase the cross-link density and hence the rigidity independently of the isocyanate-water reaction. Compounds such as glycerol, pentaerythritol and various amines have been employed as additional cross-linking agents. 

The addition of isocyanides and azide to aldehyde-derived enamines has led to tetrazoles (533,536). On the other hand the vinylogous amide of acetoacetic ester and related compounds reacted with aldehydes, isocyanides and acids to give a-acylaminoamides (534). Iminopyrrolidones and imino-thiopyrrolidones were obtained from the addition of cyclohexylisocyanide and isocyanates or isothiocyanates to enamines (535). An interesting method for the formation of organophosphorus compounds is found in the reactions of imonium salts with dialkylphosphites (536). 

Another major use of organotin compounds is as curing agents for the room temperature vulcanization of silicones the 3 most commonly used compounds are Bu2SnX2, where X is acetate, 2-ethylhexanoate or laurate. The same compounds are also used to catalyse the addition of alcohols to isocyanates to produce polyurethanes. 

The chiral bicyclic imidazolidine 74 is deprotonated at the 2 position by s-BuLi and the resulting anion adds to alkyl halides, acid chlorides, chlorofor-mates, phenyl isocyanate, and aldehydes. The use of this compound as a chiral formyl anion equivalent seems to be limited, however, since the diastereoselectiv-ity in the addition to aldehydes is poor and hydrolysis of the products 75 to give aldehydes also produces cyclohexane-1,2-diamine, necessitating isolation of the aldehyde as its 2,4-dinitrophenylhydrazone (96SL1109 98T14255). 

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