Amines to isocyanates

Addition of amines to isocyanates or isothiocyanates Addition of amines to CO2 or CS2... 

Several other reaction types on solid supports have also been investigated utilizing microwave heating. For instance, in an early report, Yu and coworkers monitored the addition of resin-bound amines to isocyanates employing on-bead FTIR measurements in order to investigate the differences in reaction progress under microwave heating and thermal conditions [63]. 

The Addition of Amines to Isocyanates A Hydro-C-alkylamino-addition... 

Phosgene produced by chlorinating carbon monoxide is used as a carbonylating agent to convert amines to isocyanates, as shown by reactions (8) and (9). Thus, the reaction of phosgene with diphenylmethane diamine results in the formation of methylene diphenyl diisocyanate (MDI), and with toluenediamine to form toluene diisocyanate (TDI). The isocyanates are used to produce polyurethanes for flexible and rigid foams, elastomers, coatings, and adhesives, for the construction and automotive industries. 

Table L Dehydration of Amines to Isocyanates Using Organic Anhydrides...

Table n. Conversion of Amines to Isocyanates Using o-Sulfobenzoic Acid Anhydride... 

Since the addition of amines to isocyanates 1005 can be regarded as the main route for the synthesis of the more challenging N,N -unsymmetrical substituted ureas 1004, isocyanates 1005 are starting reagents in many urea formation reactions. However, it is important to underline, as described in the Section 4.3.1, that isocyanates themselves are toxic and are usually prepared from phosgene [311, 747]. 

Syntheses of isocyanates from carboxylic acids/ and by the thermolysis of N-substituted 4-hydroxy-2-oxazolidones have recently appeared. In the latter method, the oxazolidones are prepared from amines and the overall reaction thus represents a conversion of amines to isocyanates without the use of phosgene. 

The intermediates in making amines are isocyanates (0==C==N) just like the Hofmann Rearrangement. The isocyanates are decomposed with water, just like the Hofmann. In fact, there is a lot of similarity between the Hofmann and the Schmidt reactions. Before I detail the synthesis steps, I should note that if you wish to generate the Hydrazoic Acid in the flask by adding Sodium Azide, you might need a powder addition funnel. This bit of equipment is quite pricey and it s likely you won t have one, so the first part of the synthesis details how to make the Hydrazoic Acid separately. 

Urea derivadves are of general interest in medicinal chemistry. They may be obtained cither from urea itself (barbiturates, sec p. 306) or from amines and isocyanates. The latter are usually prepared from amines and phosgene under evolution of hydrogen chloride. Alkyl isocyanates are highly reactive in nucleophilic addidon reactions. Even amides, e.g. sulfonamides, are nucleophilic enough to produce urea derivatives. 

The first synthetic route for isocyanates was reported in 1848 (10,11)- Subsequent efforts by Hofmann, Curtius, and Hentschel pioneered alternative synthetic approaches (12). These efforts highlighted the phosgene—amine approach. Staudinger presented the stmctural similarities between isocyanates and ketenes and stimulated interest in this class of compounds (13). However, it was not until 1945, when the world was pressed for an alternative to natural mbber, that synthetic routes to isocyanates became an area of great importance. Several excellent review articles covering the synthesis and chemistry of isocyanates have been presented (1 9). 

Both dimethyl carbonate [616-38-6] and diphenyl carbonate [102-09-0] have been used, in place of carbon monoxide, as reagents for the conversion of amines into isocyanates via this route (28,29). Alternatively, aniline [62-53-3] toluene diamines (I JJA), and methylene dianilines (MDA) have also been used as starting materials in the carbonylations to provide a wide variety of isocyanate monomers. 

Conversely, the rate of reaction of isocyanates with amines to yield ureas is both rapid and quantitative. Much has been written concerning the reaction... 

Phosgene reacts with a multitude of nitrogen, oxygen, sulfur, and carbon centers. Reaction with primary alkyl and aryl amines yield carbamoyl chlorides which are readily dehydrohalogenated to isocyanates. Secondary amines also form carbamoyl chlorides. 

A series of reactions was developed to transfer amines to ureido- and thioureido-derivatives for separation. The reaction of ureido-derivatives is widely used by the reaction with 1-phenylethyl isocyanate (PEIC) [8] or the naphthyl-analogue 1-(1-naphthyl)ethyl isocyanate (NEIC) [9]. Both reactions can be used not only for chiral amines but also for alcohols and thiols. 

Acylurea derivatives are readily prepared in one step by addition of amines to acyl isocyanates in high yields (Eqs. 1 and 2)14>. 

Addition, chloroform, to olefins to form 1,1,3 tnchloroalkanes, 46, 106 chlorosulfonyl isocyanate to isobutylene to give 0-isovaleiolactam-N-sulfonyl chloride, 46, SI cyclohexyl amine to silicon tetraiso-cyanate, 46, 69... 

Ammonia and primary and secondary amines can be added to isocyanates to give substituted ureas. Isothiocyanates give thioureas. This is an excellent method for the preparation of ureas and thioureas, and these compounds are often used as derivatives for primary and secondary amines. Isocyanic acid (HNCO) also gives the reaction usually its salts (e.g., NaNCO) are used. Wohler s famous synthesis of urea involved the addition of ammonia to a salt of this acid. "... 

According to the literature (6) the formation of urea from amine and isocyanate proceeds much faster than the formation of urethane or the hydrolysis of Isocyanate. 

---