Cyanamide reaction with ammonia

At about the same time that the Birkeland-Eyde process was developed, the Frank-Caro cyanamide process was commercialized (14). In this process limestone is heated to produce lime, which then reacts with carbon in a highly energy-demanding reaction to give calcium carbide. Reaction with N2 gives calcium cyanamide [150-62-7] which hydrolyzes to ammonia and calcium carbonate (see Cyanamides). 

Preparation. Hexagonal boron nitride can be prepared by heating boric oxide with ammonia, or by heating boric oxide, boric acid, or its salts with ammonium chloride, alkaU cyanides, or calcium cyanamide at atmospheric pressure. Elemental nitrogen does not react with boric oxide even in the presence of carbon, though it does react with elemental boron at high temperatures. Boron nitride obtained from the reaction of boron trichloride or boron trifluoride with ammonia is easily purified. 

When one mole of calcium carbonate reacts with ammonia, solid calcium cyanamide, CaCN2, and liquid water are formed. The reaction absorbs 90.1 kj of heat. 

Like the Haber process for the synthesis of ammonia, this reaction represents a way of converting elemental nitrogen into a compound (nitrogen fixation). Moreover, calcium cyanamide reacts with steam at high temperature to yield ammonia,... 

Another cyanamide compound that has a number of significant uses is sodium cyanamide, which is prepared as shown below. Sodium amide is obtained by the reaction of ammonia with Na at 400 °C. 

The introduction of Calcobond dyes a few years later by American Cyanamid exploited a similar principle but incorporated the N-methylol groups into the dye molecule itself [132]. The labile chloro substituents in dichlorotriazine dyes were converted to amino groups by substitution with ammonia and the resulting melamine residue made cellulose-reactive again by reaction with formaldehyde (Scheme 7.59). A typical member of this range was Cl Reactive Red 92 (7.120). A characteristic problem of the Procion Resin process and of the... 

At the same time a small amount of hydrogen sulphide is also eliminated. The main product of this reaction, carbodiphenylimide (di-phenylcyanamide), an extremely reactive substance, combines with the aniline present in the solution to form triphenylguanidine in the same way as, from cyanamide itself and ammonia, the unsubstituted guanidine is formed. 

Summary Precursor-derived quaternary Si-B-C-N ceramics frequently possess an enhanced thermal stability compared to SiC, SisN4 or Si-C-N ceramics. The stability of the materials towards crystallization and/or decomposition is directly coimected to the molecular structure and the elemental composition of the polymeric precursors. This paper highlights recent investigations on the synthesis of boron-modified polysilazanes and polysilylcarbodiimides. Hydroboration of polyvinylsilazanes and dehydrocoupling reactions of boron-modified silanes with ammonia or amines as well as cyanamide are described. It is shown that simple organosilicon chemistry provides a means to efficiently optimize ceramic yields and tune elemental composition as well as thermal properties of the polymer-derived ceramics. 

Other researchers have synthesized phenylcyanamides by the reaction of phenylisocyananide dihalides with ammonia,14 or by the reaction of anilines with cyanogen bromide.15 A recently prepared cyanating agent, A -cyanoimidazole, when reacted with aniline yielded phenylcyanamide in high yields under moderate conditions.16 The latter reaction may provide a route to more sensitive cyanamide derivatives. 

On treatment with diluted hydrochloric acid or sulfuric acid at 40 "C, compound 1 forms amidinobiuret 4 (73%) with loss of nitrogen. When anhydrous hydrochloric acid is added to a solution of the potassium salt of 1 in anhydrous acetone and the resulting precipitate is treated with water, 6-chloro-l,3,5-triazine-2,4-diamine (5) can be obtained. Treatment of 1 with aqueous potassium hydroxide for 24 hours leads to the isolation of 2,4-diamino-l,3,5-triazin-6(l/7)-one 6 (45%). Reaction of 1 with cyanamide in aqueous potassium carbonate solution affords 2, which gives l,3,5-triazine-2,4,6-triamine (7, melamine, 88%) together with ammonia, carbon dioxide and nitrogen when heated in diluted mineral acid. Product 7 can be obtained similarly from tetrazine derivative 3.3 See also Section B.2.3 on 1,3,5-triazines. 

AERO-CYANAMID (156-62-7) Combustible solid. Dust or powder forms explosive mixture with air. Contact with water, steam causes decomposition, forming acetylene gas, ammonia, and calcium hydrogen cyanamide. Violent reaction with strong oxidizers, fluorine, strong acids. Incompatible with barium peroxide, boric acid, dry hydrogen, hydrogen peroxide. Contact with all solvents tested also causes decomposition. 

In practice, the ammonolysis is carried out in the presence of ammonium salts—preferably ammonium nitrate—and the comparatively stable guanidine nitrate is formed. Such a technique is employed to prevent the relatively active guanidine from combining with unreacted cyanamide to form melamine. The reaction is carried out by heating calcium cyanamide, cyanamide, or dicyandiamide with ammonia and ammonium nitrate for 2 hr at 160°C under autogenic pressure. During the course of the reaction, dicyandiamide is formed from cyanamide in the presence of ammonia and, in all probability, is the primary product. The monomeric reaction is... 

Guanidine derivatives of tetrahydroisoquinoline are generally prepared by the route shown in Scheme 5.21. The von Braun reaction converts the secondary amine (84) into the cyanamide (85) and hydrogen sulphide addition in pyridine-triethylamine gives the thiourea (86). Alkylation with bromoethane and treatment with ammonia complete the preparation of debrisoquin (87) and guanisoquin (88) [95], Recently, direct reaction of (85) with anhydrous ammonia to give (87) has been achieved [96]. The two guanidines are antihypertensives of which debrisoquin is the more useful. It appears to act in part by inhibition of neuronal monoamine oxidases [97]. 

At about the same time the calcium cyanamide process was perfected. Calcium carbide, produced by reaction of lime with coke in an electric furnace, was converted to calcium cyanamide (CaCN2) by reaction with pure nitrogen extracted from the air. The product could be used directly as a fertilizer, or it could be hydrolyzed to form ammonia. 

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