Ureas from amines and

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. 

The synthesis of ureas from amines and C02 is a reversible process [125] which implies the elimination of water (Equation 6.16). 

The above methodologies, although being intrinsically valuable from a strictly synthetic point of view, are of poor interest in terms of their application. Clearly, the direct synthesis of ureas from amines and the heterocumulene (Equation 6.16), without the use of auxiliary reagents, has a greater practical significance. 

Scheme 5.13 KOH/PEG-catalyzed synthesis of symmetrical urea from amine and C02 [55]...

A recent addition to the field of functional, catalytic ionic liquids comes in the area of carbon dioxide fixation. However, in this example, the reaction was performed under solvent free conditions and the ionic liquid was just used as a catalyst. Using [Bmim][OH], yields of up to 58% were obtained for the synthesis of disubstituted ureas from amines and carbon dioxide.By considering the electrochemical reduction of carbon dioxide discussed above, it is clear that ionic liquids could have an important role to play in the area of carbon dioxide fixation. 

The historical S3mthesis of urea by heating potassium cyanate and ammonium sulfate is analogous to the synthesis of substituted ureas from amines and the cyanate ... 

Ureas from amines and carbamyl chlorides NH —y NCONRa... 

Ureas from amines and cyanogen bromide NH NGONHg... 

Moreover, the synthesis of ureas from amines and CO2 involves the elimination of water. The use of some dehydrating agents, such as carbodiimides [746] and dio-rganophosphites [744], converts this method into a direct condensation, thus offering a new synthetic process that proceeds under mild conditions. 

Scheme 32. Synthesis of dialkyl urea from amine and CO2.

Scheme 33. A proposed mechanism for the synthesis of dialkyl urea from amine and CO2 catalyzed by [BMImjOH [107].

A rapid continuous process, not complicated by side reactions, has been reported for the prepn. of isocyanato- from amino-esters. The products can be used for attaching a lyophile group to water-insoluble compounds . A new synthesis of sym. ureas from amines and carbon monoxide has been reported . ... 

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. 

Kim and Varma have described the preparation of a range of cyclic ureas from diamines and urea [366]. In the example highlighted in Scheme 6.203, ethylenedi-amine and urea were condensed in the presence of 7.3 mol% of zinc(II) oxide in N,N-dimethylformamide as solvent at 120 °C to furnish imidazolidin-2-one in 95% isolated yield. Key to the success of this method is that the reaction needs to be performed under reduced pressure in order to remove the ammonia formed from the reaction mixture. This method was extended to a variety of diamines and amino alcohols [366]. 

G. Direct Synthesis of Ureas and Polymers from Amines and Carbonyl Derivatives... 

The activity of some catalytic systems has been studied. For example, Deng has shown that the synthesis of symmetric ureas from aliphatic or aromatic primary amines and C02 can be promoted by catalytic amounts of CsOH in several ILs [128a], Under the working conditions employed (443 K, 6 MPa C02 pressure), the best activity was shown by the system CsOH/BMImCl, whilst the urea yields (up to 98% within 4h, for N,N -dicyclohexylurea) were shown to depend on the amine used. Aromatic amines, such as aniline or p-methoxyaniline, were less reactive than their aliphatic counterparts and afforded the relevant urea in modest yield (27 and 33%, respectively), but only after long reaction times (36 h). In a later study, the same group showed that the synthesis of disubstituted symmetric ureas (RNH)2CO (R = alkyl) from amines and C02 could be promoted also by catalytic... 

Peterson SL, Stucka SM, Dinsmore CJ (2010) Parallel synthesis of ureas and carbamates from amines and C02 under mild conditions. Org Lett 12(6) 1340-1343... 

The alkyl-, alky laryl- and diarylcarbodiimides are the diimides derived from carbon dioxide, however, no direct formation of carbodiimides from amines and carbon dioxide is known. Interestingly, carbodiimides can be obtained from amines and carbon dioxide via a switteri-onic titanium complex (see Section 2.2.8). The major starting materials for the synthesis of carbodiimides are isocyanates, 1,3-disubstituted ureas or 1,3-disubstituted thioureas. The synthesis of isocyanates requires the use of the toxic carbonyl chloride or its oligomers. A book on the synthesis and reactions of isocyanates appeared in 1996. ... 

Second-order reactions of type II are probably among the most common of all reactions studied. A few typical examples are the gas-phase formation of hydrogen iodide, II2 + I2 2HIthe reactions of free radicals with molecules, for example, H + Br2 HBr + H the famous synthesis of urea from NH4 and CNO ions the hydrolysis of organic esters in non-aqueous media and the reaction of tertiary alkyl amines with alkyl halides to produce quaternary ammonium salts, R3N + R X — R RsN+ +... 

Substituted ureas were prepared from amines and urea in the presence of a catalyst mixture containing DBU (81GEP2943480 82MIP2481699 85USP4501915). 

Ureas can be prepared from amines and carbon dioxide.85 They can also be prepared by heating amines with urea at 160°C.86 Treatment with excess alcohol (or other hydroxyl compound) would give a carbamate (or analogue) for pyrolysis to an isocyanate (2.36). 

Table 6 summarises the ureas and thioureas derived from amines and used in analysis. 

Hydrogen peroxide Sym. ureas and 1,3-heterocyelies from amines and carbon oxysulfide... 

Breitler S, Oldenhuis NJ, Fors BP, Buchwald SL (2011) Synthesis of unsymmetrical diarylureas via Pd-catalyzed C-N cross-coupling reactions. Org Lett 13(12) 3262-3265 Hooker JM, Reibel AT, Hill SM, Schueller MJ, Fowler JS (2009) One-Pot, Direct Incorporation of [ C]C02 into Carbamates. Angew Chem Int Ed 48(I9) 3482-3485 Peterson SL, Stucka SM, Dinsmore CJ (2010) Parallel synthesis of ureas and carbamates from amines and CO2 under mild conditions. Org Lett 12(6) 1340-1343 Wei Y, Liu J, Lin S, Ding H, Liang F, Zhao B (2010) Acetoacetanilides as masked isocyanates facile and efficient synthesis of unsymmetrically substituted ureas. Org Lett 12 (19) 4220 223... 

Jiang, T Ma, X. Zhou, Y Liang, S. Zhang, J. Han, B. Solvent-free Synthesis of Substituted Ureas from CO and Amines with a Functional Ionic Liquid as the Catalyst. Green Chem., 2008,10,465 69. 

An excess of phosgene is used during the initial reaction of amine and phosgene to retard the formation of substituted ureas. Ureas are undesirable because they serve as a source for secondary product formation which adversely affects isocyanate stabiUty and performance. By-products, such as biurets (23) and triurets (24), are formed via the reaction of the labile hydrogens of the urea with excess isocyanate. Isocyanurates (25, R = phenyl, toluyl) may subsequendy be formed from the urea oligomers via ring closure. 

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

Succinic acid reacts with urea in aqeous solution to give a 2 1 compound having mp 141°C (116,117), which has low solubiUty in water. A method for the recovery of succinic acid from the wastes from adipic acid manufacture is based on this reaction (118,119). The monoamide succinamic acid [638-32-4] NH2COCH2CH2COOH, is obtained from ammonia and the anhydride or by partial hydrolysis of succinknide. The diamide succinamide [110-14-3], (CH2C0NH2)2, nip 268—270°C, is obtained from succinyl chloride and ammonia or by partial hydrolysis of succinonitrile. Heating succinknide with a primary amine gives A/-alkylsucckiknides (eq. 9). 

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