Calcium cyanamide

Structural formula
${\displaystyle \mathrm {Ca^{2+}\;[^{-}N{=}C{=}N^{-}]} }$
General
Surname	Calcium cyanamide
other names	Calcium cyanamide
Molecular formula	CaCN 2
Brief description	colorless, hexagonal crystals
External identifiers / databases
CAS number 156-62-7 EC number 205-861-8 ECHA InfoCard 100.005.330 PubChem 56955933 ChemSpider 21106503 DrugBank DB09116 Wikidata Q367994
properties
Molar mass	80.11 g mol −1
Physical state	firmly
density	2.29 g cm −3 (20 ° C)
Melting point	1340 ° C
boiling point	sublimed from 1150 ° C
solubility	hydrolysis with water
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 261-302-317-318-335 P: 231 + 232-261-280-305 + 351 + 338-422
MAK	DFG : 1 mg m −3 (inhalable aerosol fraction) Switzerland: 0.5 mg m −3 ( respirable dust ) Austria: 0.5 mg m −3 (inhalable fraction)
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Calcium cyanamide is also known as calcium cyanamide . This trade name was suggested by Albert Frank (son of Adolph Frank ) and Hermann Freudenberg in 1901 . Both headed the Cyanidgesellschaft mbH Berlin from 1899 to 1908.

history

In their search for a new process for the production of cyanides for gold extraction by means of cyanide leaching, Adolph Frank and Nikodem Caro discovered the property of alkaline earth carbides to absorb atmospheric nitrogen at high temperatures. Fritz Rothe , a colleague of Frank and Caro, succeeded in 1898 in overcoming problems with the use of calcium carbide and in clarifying that the reaction at around 1100 ° C did not form calcium cyanide, but calcium cyanamide (calcium cyanamide). In fact, the actual target product sodium cyanide can also be obtained from calcium cyanamide by melting it with sodium chloride in the presence of carbon:

${\displaystyle \mathrm {CaCN_{2}+2\ NaCl+C\longrightarrow \ 2\ NaCN+CaCl_{2}} }$

Frank and Caro developed the process of calcium cyanamide synthesis, which is difficult in terms of apparatus due to the high temperatures - in particular through the process step of the initial ignition - into a continuous production process that can be handled on an industrial scale. In 1901 Ferdinand Eduard Polzeniusz patented a process that converts calcium carbide into calcium cyanamide in the presence of 10% calcium chloride at 700 ° C. The advantage of a reaction temperature lower by approx. 400 ° C is put into perspective by the high addition of calcium chloride and the discontinuous process management. Nevertheless, both processes, the Rothe-Frank-Caro process and the Polzeniusz-Krauss process, became established in the first half of the 20th century. In the record year 1945, a total of around 1.5 million tons were produced worldwide using both processes. Frank and Caro also noticed the formation of ammonia from calcium cyanamide.

${\displaystyle \mathrm {CaCN_{2}+3\ H_{2}O\longrightarrow \ 2\ NH_{3}+CaCO_{3}} }$

Albert Frank recognized the fundamental importance of this reaction as a technical breakthrough in the provision of ammonia from atmospheric nitrogen and in 1901 recommended calcium cyanamide as a nitrogen fertilizer. Between 1908 and 1919, five calcium cyanamide plants with a total capacity of 500,000 tons per year were built in Germany, because calcium cyanamide, as the cheapest nitrogen fertilizer at the time, with additional effectiveness against weeds and pests, had great advantages over conventional nitrogen fertilizers. The large-scale implementation of direct ammonia synthesis using the Haber-Bosch process soon gave rise to serious competition for the very energy-intensive Frank-Caro process. After the Second World War, at the latest, urea, which was considerably richer in nitrogen (46% compared to approx. 20% N content), cheaper available and faster acting urea gradually reduced calcium cyanamide to a multifunctional nitrogen fertilizer in niche applications. The dirty black color of the highly dusty calcium cyanamide powder, which irritates eyes and mucous membranes, as well as its property of inhibiting an alcohol-degrading enzyme in the human body, so that when alcohol is consumed at short notice, a temporary accumulation of acetaldehyde in the body and thus dizziness, nausea and hot flashes result can be, contributed not insignificantly to the loss of popularity of calcium cyanamide.

presentation

It can be produced by exothermic azotization of calcium carbide at 1000 ° C. Calcium cyanide is formed as an intermediate product . Since the reaction is exothermic, it can be initiated by initial ignition of a small amount using electric heating rods:

${\displaystyle \mathrm {CaC_{2}+N_{2}\longrightarrow \ Ca(CN)_{2}} }$

${\displaystyle \mathrm {\longrightarrow \ Ca^{2+}\ ^{-}N=C=N^{-}\ +C} }$

A modern variant of the technical process uses a mixture of approx. 80% by weight calcium carbide, 20% by weight calcium cyanamide and <1% by weight calcium fluoride as a reaction accelerator. The reaction takes place in a rotary kiln at 1050 ° C under nitrogen with an azotization yield of> 93%, a residual carbide content of approx. 0.1% and an N content of the calcium cyanamide produced of> 24.5%. If a cheap urea source is available, a two-stage process that runs at significantly lower temperatures can also be used to produce calcium cyanamide. In the first step, calcium cyanate is produced from urea and calcium oxide at approx. 250 ° C, which in the second step at approx. 750 ° C to pure calcium cyanamide in up to 97% yield and an N content of the calcium cyanamide produced of up to 34 % is implemented.

use

Implementation of calcium cyanamide in the soil

Calcium cyanamide is used as a starting material for the synthesis of cyanamide , dicyandiamide , melamine , thiourea or guanidines .

Under the name of calcium cyanamide , it is one of the fertilizers approved in the European Union and, due to the cyanamide that is formed in the course of the conversion into plant-available nitrogen forms, has a killing effect on various weeds, animal pests, pasture parasites and plasmodia of Plasmodiophora brassicae . For the latter use, calcium cyanamide was approved as a pesticide in the 1980s by the Federal Biological Institute, which was still responsible for pesticide approval at the time.

properties

Commercially available calcium cyanamide is usually still contaminated with carbon , calcium oxide , iron and aluminum . It then usually has a gray to black color. When dissolved in water, it decomposes into ammonia and calcium carbonate .

safety instructions

Calcium cyanamide in combination with ethanol can lead to hyperaemia of the skin , dizziness and shortness of breath . The alcohol intolerance reaction is triggered by the cyanamide formed in the body, which, like disulfiram , which is used as an alcohol aversion, induces the accumulation of toxic acetaldehyde in the bloodstream by inhibiting acetaldehyde dehydrogenase . The symptoms of poisoning reappear in a weaker form in the long term after subsequent contact with alcohol or other acetaldehyde-forming substances. This is known as calcium cyanamide disease .

Web links

• Conversion of calcium cyanamide in the soil from www.alzchem.com, accessed on March 14, 2017
• Potential risks to human health and the environment from the use of calcium cyanamide as fertilizer (PDF 1534 kB, Scientific Committee on Health and Environmental Risks , 2016)

Individual evidence

1. ↑ ^{a b} Entry on calcium cyanamide. In: Römpp Online . Georg Thieme Verlag, accessed on October 25, 2014.
2. ↑ ^{a b c d e f g} Entry on calcium cyanamide in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
3. ↑ Entry on Calcium cyanamide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 156-62-7 or calcium cyanamide ), accessed on November 2, 2015.
5. ↑ Limit values ​​for working materials ( Memento of the original from September 23, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Ordinance of the Federal Minister for Labor, Social Affairs and Consumer Protection (Limit Values ​​Ordinance GKV 2011), Austria.  
6. ↑ German Imperial Patent DRP 88363, “Process for the preparation of cyano compounds from carbides”, inventor: A. Frank, N. Caro, granted on March 31, 1895.
7. ^ HH Franck, W. Burg: To the chemistry of the calcium cyanamide. V. In: Journal of Electrochemistry and Applied Physical Chemistry , Vol. 40, 1934, pp. 686-692. doi : 10.1002 / bbpc.19340401004
8. ^ ACS Chemical Landmarks 1998, "Discovery of the commercial processes for making calcium carbide and acetylene".
9. ↑ Angewandte Chemie, Volume 29, Issue 16, page R97, February 25, 1916.
10. ↑ DE-Patent 3705049C2, applicant: SKW Trostberg AG, issued on August 1, 1991.
11. ↑ US Patent 5,753,199, Applicant: SKW Trostberg AG, issued May 19, 1998.
12. ↑ "Aversion drugs strengthen long-term abstinence from alcohol" , research report by the Max Planck Society, January 9, 2006.