Hydrolysis urea complexes

Addition of water to coordinated isocyanato groups has been suggested97 as an intermediate step in the conversion of a pentammine rhodium(III) urea complex to the related hexammine complex (Scheme 22) and also in the nickel(II)-promoted hydrolysis of a pyridylurea (Scheme 23). The isocyanato intermediate has been observed in the first example but not the second. 

The simplest and most efficient technique for obtaining 0)3 PUFA concentrates in the form of free fatty acids is urea complexation. This technique is well established for elimination of saturated and monounsaturated fatty acids (70). In this method, the saturated and monounsaturated fatty acids can easily complex with urea after hydrolysis of TAG with aUcaline, and crystallize out on cooling and may subsequently be removed by filtration (70). This method is favored by many researchers because complexation depends on the configuration of the fatty acid moieties because of the presence of multiple double bonds, rather than of pure physical properties such as melting point or solubility (10). 

Coordinated cyanamide does not add OH" to form the N-bound urea complex since it de-protonates 5.2) to ve the unreactive [Co(NCNH)(NH3)5p ion, but in acid it readily loses NH to form N-coordinated cyanate (equation 27). The analogous dimethylcyanamide complex cannot deprotonate and adds OH" to form urea (Scheme 21), but this does not proceed further to coordinated carbamic add and NHMCj in a process analogous to that suggested for the function of Ni in the metalloenzyme jack bean urease (which catalyzes the convemioo of urea to these products), nor does it lose NHMc2 to form the cyanato complex as suggested by Balahura and Jordan for the similar urea derivatives (equation 28). Alternatively, in acid solution the protonated urea rapidly isomerizes to the O-coordinated complex (r,/2 a 40 s, 25 °C Scheme 21). This isomer undergoes OH -catalyzed hydrolysis at the metal rather than at acyl carbon, so the function of the metalloenzyme has not been duplicated in this system. A similar property is found for 0-bound urea (equation 29). ... 

Both complexes (867) and (868) promote the hydrolysis of urea in a two-step process.2080 Heating of (867) or (868) in acetonitrile solution produced ammonia with kinetic first-order dependence on complex concentration and an observed rate constant of (7.7 0.5) x 10-4 h-1 to yield a cyanate complex as the reaction product. When the reaction was carried out in 50% aqueous acetonitrile solution, ammonia was produced at the same rate but without buildup of the cyanate-containing product, suggesting that the latter is hydrolyzed in the presence of water. The hydrolysis rate was also first order in water, indicating that it occurred by attack of an external water on the coordinated cyanate.2080... 

Figure 36 Complexes catalyzing hydrolytic cleavage of peptides, hydrolysis and alcoholysis of nitriles, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various...

More than 25 different substituted urea herbicides are currently commercially available [30, 173]. The most important are phenylureas and Cycluron, which has the aromatic nucleus replaced by a saturated hydrocarbon moiety. Benzthiazuron and Methabenzthiazuron are more recent selective herbiddes of the class, with the aromatic moiety replaced by a heterocyclic ring system. With the exception of Fenuron, substituted ureas (i.e., Diuron, Fluometuron, Fig. 10, Table 3) exhibit low water solubilities, which decrease with increasing molecular volume of the compound. The majority of the phenylureas have relatively low vapor pressures and are, therefore, not very volatile. These compounds show electron-donor properties and thus they are able to form charge transfer complexes by interaction with suitable electron acceptor molecules. Hydrolysis, acylation, and alkylation reactions are also possible with these compounds. 

Hydrolysis of the ester forms adipic acid, used to manufacture nylon—6. Carbonylations of nitroaromatics are used to synthesize an array of products including amines, carbamates, isocyanates, ureas and azo compounds. These reactions are catalyzed by iron, ruthenium, rhodium and palladium complexes. For example, carhonylation of nitrobenzene in the presence of methanol produces a carbamate ... 

The reactions of the pentaamminecobalt(III) complex of urea (O-coordinated) have also been studied.506 Under basic conditions [Co(NH3)5OH]2+ is the only cobalt(III) product. The main reaction pathway (ca. 97%) is SN1CB displacement of coordinated urea (Scheme 40) with kOH = 15.3 M s-1 at 25 °C. A limiting rate was approached at high pH as the complex dissociated to its inactive conjugate base. Hydrolysis of coordinated urea was not observed. 

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