Cyanamides formation

The main important chemical property of N2 is its very high inertia to chemical reactions. As is well known from the technical realization (Haber-Bosch-method, Birkeland-Eyde-method or cyanamid formation by the use of calciumcarbide, see Ref.6 ) special reaction conditions are necessary for N2-fixation, which are not applicable in biological systems. Hence, special catalysts of high activity at room temperature are required. 

The solubility of the carbonate in water containing carbon dioxide causes the formation of caves with stalagtites and stalagmites and is responsible for hardness in water. Other important compounds are the carbide, chloride, cyanamide, hypochlorite, nitrate, and sulfide. 

Aminothiazole derivatives (243) can be prepared by treatment of enamines of type 240 with sulfur and cyanamide at room temperature in ethanol (701) yields range from 30 to 70%, and no catalyst is required. Initial formation of the thiolated intermediate (241) is probably followed by addition of cyanamide, yielding 242 (Scheme 124). 

Processes rendered obsolete by the propylene ammoxidation process (51) include the ethylene cyanohydrin process (52—54) practiced commercially by American Cyanamid and Union Carbide in the United States and by I. G. Farben in Germany. The process involved the production of ethylene cyanohydrin by the base-cataly2ed addition of HCN to ethylene oxide in the liquid phase at about 60°C. A typical base catalyst used in this step was diethylamine. This was followed by liquid-phase or vapor-phase dehydration of the cyanohydrin. The Hquid-phase dehydration was performed at about 200°C using alkah metal or alkaline earth metal salts of organic acids, primarily formates and magnesium carbonate. Vapor-phase dehydration was accomphshed over alumina at about 250°C. 

Urea is dehydrated to cyanamide which trimerizes to melamine in an atmosphere of ammonia to suppress the formation of deamination products. The ammonium carbamate [1111-78-0] also formed is recycled and converted to urea. For this reason the manufacture of melamine is usually integrated with much larger facilities making ammonia and urea. 

Hydrogen sulfide reacts with nitriles in the presence of a basic catalyst forming thioamides. A commercial example is its addition to cyanamide with the formation of thiourea [62-56-6]. ... 

The calcium cyanamide feed is weU mixed with the recycled slurry and filtrate ia a feed vessel. The calcium cyanamide is added at a rate to maintain a pH of 6.0—6.5 ia the cooling tank. The carbonation step can be conducted ia a turbiae absorber with a residence time of 1—2 min. After the carbonation step, the slurry is held at 30—40°C to complete the formation of calcium carbonate, after which the slurry is cooled and filtered. AH equipment for the process is preferably of stainless steel. The resulting solution is used directiy for conversion to dicyandiamide. 

Specifications and Analysis. Cyanamide is sold as anhydrous, aqueous 50%, and calcium cyanamide. Aqueous 50% cyanamide solutions contain a buffer additive, usually 2% NaH2P04, to stabilize the pH and prevent formation of dicyandiamide and urea. Calcium cyanamide is stable under dry conditions. Table 2 gives a typical analysis of the three commercial forms. 

Traces of cyanamide can be deterrnined colorknetricaHy by complex formation with l,2-naphthaquinone-4-sodium sulfonate (4). 

No reaction takes place below 500°C when sodium cyanide and sodium hydroxide are heated in the absence of water and oxygen. Above 500°C, sodium carbonate, sodium cyanamide [19981-17-0] sodium oxide, and hydrogen are produced. In the presence of small amounts of water at 500°C decomposition occurs with the formation of ammonia and sodium formate, and the latter is converted into sodium carbonate and hydrogen by the caustic soda. In the presence of excess oxygen, sodium carbonate, nitrogen, and water are produced (53). 

The aqueous decomposition of thiourea to sulfide and cyanamide has been found to be catalyzed by metal hydroxide species and colloidal metal hydroxide precipitates. Kitaev suggested that Cd(OH)2 is actually required for CdS film formation to occur by adsorption of thiourea on the metal hydroxide particles, followed by decomposition of the Cd(OH)2-thiourea complex to CdS. Kaur et al. [241] found... 

Homo- and heteroleptic complexes of Cd alone and of Cd and Hg with the ligand dicyanamide (dca) N(CN)2-, homologous to cyanamide NCN2-, have been studied in various solvents (formation constants of the complexes [M(dca) ](" 2> (M = Cd, Hg l < n < 4)), with the result that the complexes of Hg are more stable than those of Cd. Otherwise, obviously no studies on the isolated compounds M(dca)2 or on homoleptic complexes derived therefrom have been published. 

The influence of nitrogen fertilizer source on the germination rate of ergots placed on the ground in rye culture has been studied. Compared with calcium ammonium nitrate, application of calcium cyanamide reduced the germination of ergots and formation of perithecia by 40-50% (Mielke, 1993). 

Pearl calcium cyanamide is able to reduce germination of ergots and formation of perithecia better than calcium ammonium nitrate in conventional farming. 

Marcotrigiano et al.39 suggested that the desulfuration of thiourea in sodium hydroxide results in the formation of cyanamide, amidinourea, and guanidine at a pH below 12 they also suggested that the formed urea converts to ammonium cyanate and finally to ammonium carbonate (by hydrolysis). The pro-... 

We are investigating the template formation of 2-D and 3-D metal-di-cyanamide anionic networks, for instance of type Mn(dca)3, by use of [M(N,N)3]n+ cations such as [M(2,2 -bipy)3]2+. A hexagonal sheet network was formed in [Fen(2,2 -bipy)3][Fen(dca)3]2 in which the cations fitted beautifully within the hexagonal windows. The cation remained LS between 4-300 K [66], Attempts to make the Con(2,2 -bipy)32+ analogue unfortunately led to dissociation of dca and bipy and formation of a zig-zag chain structure in the weakly-coupled HS complex [Con(dca)2(2,2 -bipy)2]n. The complex [Fen(propyl-tetrazole)6]2+, which has a very sharp SCO transition [42], unfortunately did not yield a network product. 

An interesting legal case ensued in the English High Court [87], where Ethicon (Johnson Johnson) maintained, among other things, that the formation and hydrolytic behaviour of polyglycolide fibres were already known and that it was therefore obvious to use the material as an absorbable suture. The outcome was basically favourable to American Cyanamid. 

The formation of a biguanide as a by-product in a condensation of a cyanamide and amine (225) (which would normally be expected to yield a guanidine) and as main product in the reaction of glucosamine and cyanamide (437) has been noted. In the former example, the small amount of biguanide probably arose by further reaction of the primary guanidine (which formed the main product) with C5 namide. In the second example the biguanide may be the result of the interaction of the amine and intermediate cyanoguanidine. 

Odo studied the formation of methylguanidine from cyanamide and aqueous mixtures of methylamine and methylamine hydrochloride in various proportions [ 110]. He concluded that the reaction occurred by a reversible nucleophilic attack of the free amine on cyanamide, and that an acid was required to shift the equilibrium in the direction of the guanidine. 

A technical exploitation of these experiments appeared unattractive, until 1909. Other methods of the chemical fixation of nitrogen, particularly the electric arc process for the formation of nitrous oxides (18) and the calcium cyanamide process (19) appeared far superior at that time. 

The interaction of cyanogen bromide vapors with solid o-hydroxyaniline (236u) or the solid benzhydrazides 324 at room temperature provides the 2-aminobenzoxazole (433) or the 2-amino-5-aryl-aminooxadiazole salts 434 [92] (Scheme 68). These 3-cascades imply formation of the cyanamide, its cyclization, and tautomerization. 

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