Calcium cyanamide reactions

The synthesis of these disubstituied thioureas takes place in three steps. First the alkyl bromide is prepared by the action of hydrobromic acid on the corresponding alcohol (518). Then the dialkylcyanamide is obtained by treatment at 25°C with calcium cyanamide. The yields are of the order of 30 to 60%. Thioureas are obtained in a third step from the cyanamide by reaction at 40 C with HjS in the presence of pyridine. Yields ranged from 57 to 90% (518),... 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

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. 

Reaction With Nitrogen. Calcium cyanamide is produced from calcium carbide... 

Reaction of lime and urea forms calcium cyanate [6860-10-2] (26) which is then converted to calcium cyanurate [32665-90-0], the latter gives calcium cyanamide at a higher temperature ... 

Health and Safety Factors (Toxicology). Manufacture of cyanamide and calcium cyanamide does not present any serious health hazard. Ingestion of alcohoHc beverages by workmen within several hours of leaving work sometimes results in a vasomotor reaction known as cyanamide flush. Cyanamide interferes with the oxidation of alcohol and accumulation of acetaldehyde probably accounts for this temporary phenomenon. Although extremely unpleasant, it has not been known to result in serious illness or to have any permanent effect. 

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. 

The reaction CaC2 I N, CaCN2 + C produces calcium cyanamide, which has been widely used as a fertilizer. Draw the structure of the cyanamide ion and describe the bonding. 

Calcium acetylide is used in the manufacture of calcium cyanamide, CaCN2, by the reaction of CaC2 with N2 at high temperature. 

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,... 

Although relatively few compounds contain only carbon and nitrogen, derivatives such as the cyanides have commercially important uses. Also, calcium cyanamide, CaCN2, can be prepared by the reaction... 

Guanidines have been prepared by the reaction between an amine, or an amine salt, and a host of other reagents, such as a thiourea in the presence of lead or mercuric oxide [83, 157, 158], carbodi-imides [140, 174, 175],calcium cyanamide [176, 177], isonitrile dichlorides [178—180], chloroformamidines [181], dialkyl imidocarbonates [182], orthocarbonate esters [183], trichloro-methanesulphenyl chloride [184], and nitro- or nitroso-guanidines [185-188]. Substituted ureas can furnish guanidines, either by treatment with amines and phosphorus oxychloride [189], or by reaction with phenylisocyanate [190] or phosgene [191]. 

Reaction with nitrogen at elevated temperatures produces calcium cyanamide, used as a fertilizer ... 

Calcium cyanamide partially hydrolyzes to calcium hydrogen cyanamide, CaHCN2. The final hydrolysis products are calcium carbonate and ammonia. The reaction is slow, occurring in moist soil ... 

The addition of the calcium cyanamide to the acid should be slow enough to ensure thorough mixing and to prevent the reaction mixture from becoming hot. 

An autoclave (7) is supplied with an aqueous solution that contains 600 g of ammonium nitrate and 40 g of ammonia per litre. Calcium cyanamide in the ratio of 500 g CaCN2 to every litre of solution is then added from container (2) after being weighed at (3). The autoclave is closed, carbon dioxide is introduced, while the contents are cooled with water so that the temperature does not exceed 100°C. When no more carbon dioxide is absorbed, the supply is stopped, and so is the inflow of cooling water. The reaction mixture is now steam heated to 160°C. Afterwards a communicating valve joining the autoclave (7) with a second autoclave (75) is opened. The other vessel (75) is filled with ammonium nitrate solution prepared for the next charge. In this way the major part of the ammonia passes from autoclave (7) over to autoclave (75). After the reaction is finished the mixture is raised from the auto-... 

Cyanide. Potassium cyanide, [CAS 151-50-8], cyanide of potash, KCN, white solid, soluble, very poisonous, formed by reaction of calcium cyanamide and potassium chloride at high temperature. Used as a source of cyanide and for hydrocyanic acid, but usually replaced by the cheaper sodium cyanide. Also used in metallurgy, electroplating,... 

Dicyandiamide, which is readily obtainable from calcium cyanamide and is a stable commercial product, may be converted into guanidine nitrate by the action of ammonium nitrate, either in concentrated aqueous solution under pressure12,13 or by a fusion reaction.13-16 The latter procedure gives a very pure product and is to be preferred for laboratory practice. Directions for its use are given under procedure A. 

Cyanamide is also acted upon directly by ammonium salts in aqueous and non-aqueous solutions.17-20 Since it is of decided advantage to avoid the isolation of pure cyanamide, methods have been developed in which aqueous solutions of cyanamide are prepared from calcium cyanamide and are then permitted to react with ammonium salts. However, guanidine nitrate may also be prepared directly from commercial calcium cyanamide by the action of ammonium nitrate. This reaction takes place readily in the fused state, in concentrated aqueous solution,21 or by direct admixture of solid ammonium nitrate with calcium cyanamide and subsequent heating to 100°C.22 The latter procedure is to be preferred, since better yields are obtainable and the hazard of fusion with ammonium nitrate is obviated. The directions given for procedure B require the use of a fairly good grade of unoiled calcium cyanamide containing approximately 65 per cent CaNCN. 

According to Goekel,22 this reaction takes place in the following manner Dry ammonium nitrate reacts with calcium hydroxide present in the crude calcium cyanamide to give calcium nitrate, water, and ammonia. The ammonia and water do not escape but are absorbed by the calcium nitrate to give a mixture of hydrated and ammonated salt and also by the ammonium nitrate which is ammono-deliquescent (Diver s solution). These substances melt below 100°C. and provide a solvent in which the reaction between calcium cyanamide and ammonium nitrate may take place. 

Cyanamide process. Although this process employs relatively inexpensive raw materials, it cannot compete with the Haber process under normal conditions. Formation of ammonia by the cyanamide process is based on the reaction between calcium cyanamide and steam ... 

Sodium cyanide can also be prepared from calcium cyanamide by the reactions... 

Calcium cyanamide (CaNCN) is made in an impure form, largely for fertilizer use, by the reaction... 

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