N-H from urea

N-H combination band from urea (NH2-C=0-NH2) N-H (vN-H asymmetric and NH2 rocking) combination N-H from urea... 

Melamine. Melamine (cyanurotriamide, 2,4,6-ttiainino-j -triazine) C H N, is a white crystalline soHd, melting at approximately 350°C with vaporization, only slightly soluble in water. The commercial product, recrystallized grade, is at least 99% pure. Melamine was synthesized eady in the development of organic chemistry, but it remained of theoretical interest until it was found to be a usehil constituent of amino resins. Melamine was first made commercially from dicyandiamide [461-58-5] (see Cyanamides), but is now made from urea, a much cheaper starting material (9—12) (see also... 

Not only N-H bonds from amines can participate in the aminolysis reaction, but also less nucleophilic urea, thiourea and biuret NH units can react with halophosphanes in an effective manner, forming the corresponding phosphinous amides with additional functionalities at the nitrogen atom [39-44]. 

Table 2. Production of greenhouse gases, CO, CH4 (pg C kg"1 soil h ), and NzO (pg N kg"1 soil h ) from five treatments a) soil + plant + wastewater (SMWW), b) soil + plant + urea (SMUREA), c) soil + urea (SUREA), d) soil + wastewater (SWW), and e) soil + water (SCONTROL).

The removal of fertilizer N in the crop as NH4+ does not lead to acidification. Hydrolysis of urea fertilizer—by far the main form of N fertilizer used in wetland rice, together with ammonium bicarbonate in some countries—consumes 1 mol of H+ per mol of NH4+ formed (Table 7.1, Process 1). So although absorption of N as NH4+ leads to a net export of H+ from the roots to balance the resulting excess intake of cations over anions (Table 7.1, Process 5), this acidity is matched by the H+ consumed in urea hydrolysis. Likewise there is no net generation of acidity as a result of NH3 volatilization, although 1 mol of H+ is left behind per mol of NH4+ converted to NH3 (Table 7.1, Process 3). 

N—H 0 hydrogen bonds and are interlinked by the syrc-N—H 0 hydrogen bonds. (Reprinted from [9] with permission from A AAS) (b) Van der Waals cross-section of the cavity in the urea channel compared with the size of /3-octane (left), benzene (top), 3-methylheptane (right) and 2,2,4-trimethylpentane (bottom), (c) chemical structures of urea and thiourea, (d) packing of urea channels to give the honeycomb-like structure of hexagonal urea. 

Secondary amines can be cleaved from the resin either directly or after modification. Primary amines can be derivatized on the free N-H function and can therefore be modified to an array of products. Thus, ureas 81 [54], thioureas 80, guanidines 79, and carboxamides 82 were prepared in excellent yield (Scheme 6.1.17). 

The generation of H2 from reaction with molecules containing an N—H bond seems to be a general feature of 10. This has also been demonstrated by the unique dehydrogenation of urea (and substituted ureas) by 10 to yield 1 mol H2/Ti2 unit. The product contains a mixture of mono- and binuclear ureylene complexes, e.g., [(ij-C5H5)2TiN(H)C(=0)N(H)Ti(i7-C5H5)2]. 

Carboxamides form rather unstable 1 1 adducts with HFA insertion into one N—H bond occurring as with urea 202). Addition of another molecule of HFA can only be effected by salt formation with pyridine. The addition is reversible. A stable product 125a is obtained from urea in the presence of acetic acid anhydride 257). Thiourea forms the corresponding oxadiazin-thione 125b with HFA (257). 

Bernard, R., Ahmed, O.H., Majid, Ah., N.M., and JaUoh, M.B. 2009. Reduction of ammonia loss from urea through mixing with humic acids isolated from peat soil (Saprists). American Journal of Environmental Sciences, 5(3) 393-7. 

Primary ureas 1365 are good substrates in rhodium-catalyzed N-H insertion reactions with an array of 2-diazo-l,3-keto esters 1364. The products from the insertion reaction cyclize with the aid of acid to yield imidazolones 1366. This chemistry has been translated onto insoluble polymer resins and utilized to prepare a small array of imidazolones (Scheme 351) <20030L511, 2004JOC8829>. 

Also, Schellman s work is pertinent (1809). From studies on heats of dilution of urea in water he concludes that the N—H 0=C bond has an enthalpy of 1.5 kcal/mole in aqueous solution, and he carries this value over to proteins and polypeptides. Among these complicated materials he is forced to approximate—but he deduces relations which show the stability of helices and sheets in terms of H bond enthalpy and configurational entropy. From this he draws the important conclusion that H bonds, taken by themselves, give a marginal stability to ordered structures which may be enhanced or disrupted by the interactions of the side chains. Schellman ends his papers with a discussion of experimental tests needed to eliminate some of the assumptions in his theoretical analysis. 

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