Phosgene reaction with ureas

Reaction of 1,2-diaminoarenes with phosgene or urea gives 2-benz-imida/.olones (Scheme 3.1.14). The latter reagent has been preferred as it is less toxic. There are, however, a variety of other reagents which lead to the same products carbonate esters [117], diethyl pyrocarbonatc [118], N,N-diethylcarburnyl chloride [119], l,T-carbonyldiimidazole [120], cyanic acid [121] and carbon dioxide [122]. (See also reactions with ketones below.) Preston has reviewed these processes [54]. The reactions with urea (or... 

The 3- hydroxy compounds are prepared from hydrazinopyrazines by reaction with urea at 150° or by treatment with phosgene at room... 

Phosgenation. Reaction of phosgene with arylamines to form ureas, and with reactive aryl species to form substituted hen zophen ones, are special cases of acylation. They are dealt with separately siace a more specialized plant is required than for other acylations. Urea formation takes place readily with water-soluble arylamines by simply passiag phosgeae through a slightly alkaline solutioa. An important example is carbonyl-J-acid from J-acid. 

Dimethyl carbonate (DMC) is a colorless liquid with a pleasant odor. It is soluble in most organic solvents but insoluble in water. The classical synthesis of DMC is the reaction of methanol with phosgene. Because phosgene is toxic, a non-phosgene-route may be preferred. The new route reacts methanol with urea over a tin catalyst. However, the yield is low. Using electron donor solvents such as trimethylene glycol dimethyl ether and continually distilling off the product increases the yield. ... 

Guanidines have been prepared by the reaction between an amine, or an amine salt, and a host of other reagents, such as a thiourea in the presence of lead or mercuric oxide [83, 157, 158], carbodi-imides [140, 174, 175],calcium cyanamide [176, 177], isonitrile dichlorides [178—180], chloroformamidines [181], dialkyl imidocarbonates [182], orthocarbonate esters [183], trichloro-methanesulphenyl chloride [184], and nitro- or nitroso-guanidines [185-188]. Substituted ureas can furnish guanidines, either by treatment with amines and phosphorus oxychloride [189], or by reaction with phenylisocyanate [190] or phosgene [191]. 

The replacement of both -OH groups with chlorine produces Ccirbonyl dichloride, also known as phosgene, a useful reactant. For example, phosgene reacts with two moles of alcohol to form a dialkyl carbonate. The reaction of phosgene with one mole of alcohol produces an alkyl chloroformate, which is a useful intermediate in organic syntheses. The reaction of phosgene with four moles of ammonia yields urea and two moles of ammonium chloride, NH Cl. Figure 12-40 shows the structures of some of these compounds. 

Identification of Trichloromethyl Chloroformate. This substance may. be identified by its reaction with an aqueous solution of aniline (3 100). Like phosgene and dichloromethyl chloroformate, a white crystalline precipitate of diphenyl urea forms, which may be confirmed by microscopic examination (rhombic prisms) or by a determination of its melting point (236° C.). 

The reaction of phosgene with substituted ureas is well known. Phosgene reacts with tetrasubstituted ureas as a chlorinating agent to afford chloroformamidinium chlorides in high yields. This topic will be discussed in volume 2. 

Mixing of two different aminoazo compounds, followed by reaction with phosgene, gives the asymmetricai urea, in addition to the two symmetrical products [992a] ... 

By-products, including urea, are generated by reaction of the generated ammonia with unreacted phosgene. In contrast, gaseous phosgene reacts with solid sodium amide at 250 C to form sodium cyanamide [1605] ... 

Phosgene reacts with amidobenzyl piperidines (substituted at the 2-, 3-, or 4- aromatic ring positions) at room temperature to give the corresponding amidobenzyl chlorides, and a substituted urea. The reaction is typified by that shown for the 2-isomer [1179a] ... 

Whereas the reaction of MCjNNHj with phosgene results in the formation of the urea, MejNNHCCOlNHNMej, protection with a silyl group prior to reaction with phosgene results in... 

The reaction of Me jCPCSiMe 3) j with phosgene occurs with the elimination of Me3SlCl and CO, and the formation via several detectable intermediates) of a cyclic phospha-urea derivative, (10.31), as illustrated in the following scheme [71] ... 

Similarly, the reaction with aniline itself proceeds differently. With phosgene, aniline gives the simple disubstituted urea (see Section 10.2.1.1), whereas it reacts with carbonyl dibromide in diethyl ether to yield a disubstituted urea, but with the phenyl rings 4-brominated [1937a] ... 

Reactions with nucleophiles other than alcohols can produce other carbonic acid derivatives. For example, reaction with anhydrous ammonia yields urea, 0 = C(NH2)2. Aromatic primary amines can, depending on reaction conditions, react with phosgene to form carbamoyl chlorides (Csuros et al., 1969). 

Urea is obtained from the reaction between C02 with NH3 at high temperature and pressure. It can also be produced by the reaction of phosgene gas with ammonia. 

The reaction of urea or phosgene with amino acids gives 1 -labeled hydantoins with potential utility as radiopharmaceuticals.26... 

Polyureas (8). Many synthetic methods for preparation of polyureas are known. Examples of reactions that can be used for the preparation of a variety of polyurea structures include reaction of diamines with phosgene (Reaction 21), with urea (Reaction 22) or with diisocyanates (Reaction 23). 

Perimidinones are available from 1,8-naphthalenediamines in cyclization reactions with potassium cyanate, carbonate, and chlorocarbonate esters, phosgene, and urea all methods give satisfactory results. 2-Alkoxy- and aryloxyperimidines are readily available by nucleophilic substitution reactions in the 2-position <81RCR8I6>. 

It is, however, also possible to start with the free amine, provided that reaction is first converted with an excess of phosgene in the cold. The amine, sometimes in solution, is usually added to a cooled solution of an excess of phosgene the symmetrical urea derivative is not formed under these conditions, but instead a mixture of the amine hydrochloride and the carbamoyl chloride which then reacts further with phosgene as described above. For instance, the 4,4 -diisocyanate from diphenylmethane was prepared in this way.629... 

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