Calcium cyanamide

Cyanamide

Colorless, hexagonal crystals

Fixed

2.29 g · cm -3 ( 20 ° C)

1340 ° C

Sublimated from 1150 ° C

With water hydrolysis

Risk

1 mg · m-3

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Calcium cyanamide is also known as calcium cyanamide. These trade names proposed before 1901 Albert Frank (son of Adolph Frank) and Hermann Freudenberg. Both initiated from 1899 to 1908 the Cyanidgesellschaft mbH Berlin.

History

In their search for a new process for the production of cyanide for gold recovery by cyanidation discovered Adolph Frank and Nikodem Caro the property of Erdalkalicarbiden to take atmospheric nitrogen at high temperatures. Fritz Rothe, an associate of Frank and Caro, succeeded in 1898 to overcome problems in the use of calcium carbide and to clarify that during the reaction at about 1100 ° C, no calcium cyanide, but calcium cyanamide ( calcium cyanamide ) is formed. In fact, can be derived from calcium cyanamide by fusion with sodium chloride in the presence of carbon and the actual target product sodium cyanide win:

Frank and Caro developed the terms of apparatus difficult because of the high temperatures of calcium cyanamide process - in particular through the process step of initial spark - to a large technically manageable continuous production process. In 1901, Ferdinand Eduard Polzeniusz a process was patented, which converts the calcium carbide in the presence of 10 % calcium chloride at 700 ° C to calcium cyanamide. The advantage of a lower by about 400 ° C reaction temperature is, however, offset by the high calcium chloride addition and the discontinuous process control. Nevertheless, both processes, the Rothe - Frank - Caro process and the Polzeniusz Krauss method in the first half of the 20th century have been established. In the record year 1945 a total of approximately 1.5 million tons were produced by both methods around the world. Frank and Caro found the formation of ammonia from cyanamide.

Albert Frank recognized the fundamental importance of this reaction as a technical breakthrough in the provision of ammonia from atmospheric nitrogen and recommended in 1901 calcium cyanamide as a nitrogen fertilizer. Between 1908 and 1919 five Kalkstickstoffwerke were built with a total capacity of 500,000 tons per year, as calcium cyanamide as time billigster nitrogen fertilizer with additional efficacy against weeds and pests had great advantages over conventional nitrogen fertilizers in Germany. Due to the large-scale implementation of the direct synthesis of ammonia by the Haber - Bosch process, the very energy-intensive Frank - Caro process already arose soon serious competition. The essential nitrogen-richer at the latest after the Second World War ( 46% versus 20% N content ), available cheaper and faster effective urea reduced gradually to a multifunctional calcium cyanamide nitrogen fertilizer in niche applications. The dirty - black color of the large amount of dust, eyes and mucous membranes lovely Kalkstickstoffpulvers, and the required strict abstinence from alcohol the user before, during and immediately after application of calcium cyanamide contributed considerably in the loss of popularity of calcium cyanamide.

Representation

It can be produced by exothermic Azotierung of calcium carbide at 1000 ° C. As an intermediate calcium cyanide appears with it. Since the reaction is exothermic, it can be initiated by detonation of a small amount by means of electrical heating elements:

The technical procedures used in a modern variant is a mixture of about 80 % by weight of calcium carbide, 20 wt % calcium cyanamide and <1 wt % of calcium fluoride as a reaction accelerator. The reaction proceeds in a rotary kiln at 1050 ° C under nitrogen in a Azotierausbeute of> 93 %, a Restcarbidgehalt of about 0.1% and an N content of the produced lime nitrogen of> 24.5%. If a cheap urea source is available, also a period ending at much lower temperatures two-stage process for the production of calcium cyanamide can be used. In the first step is generated from urea and calcium oxide at about 250 ° C Calciumcyanat, in the second step at about 750 ° C to pure calcium cyanamide in a yield of up to 97% and an N content of the produced lime nitrogen of up to 34 % is implemented.

Use

Calcium cyanamide is cleaned of calcium carbide, calcium cyanamide as a fertilizer on the market. It serves as a starting material for the synthesis of cyanamide, dicyandiamide, melamine, thiourea or guanidine.

Calcium cyanamide is one of the approved in the European Union and fertilizers has brassicae due to the arising in the course of the reaction to plant-available forms of nitrogen cyanamide a killing effect on various weeds, animal pests, parasites pasture and plasmodia of Plasmodiophora. For the latter purpose cyanamide was approved in the 1980s, by the time its still responsible for pesticide registration BBA as plant protection products.

Properties

Commercial calcium cyanamide is usually also containing carbon, calcium, iron and aluminum contaminated. It then typically a gray to black color. When dissolved in water it decomposes into ammonia and calcium carbonate.

Safety

Calcium cyanamide, in conjunction with ethanol lead to hyperemia of the skin, dizziness, trouble breathing. Trigger of alcohol intolerance reaction is the cyanamide formed in the body, which induces as the disulfiram used as ADs by inhibiting acetaldehyde accumulation of toxic acetaldehyde in the bloodstream. This is known as calcium cyanamide disease.