Calcium cyanamide

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Calcium cyanamide
CaCN2Xray.tif
Calcium cyanamide.png
Names
IUPAC name
Calcium cyanamide
Other names
Cyanamide calcium salt, Lime Nitrogen, UN 1403, Nitrolime
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.005.330
EC Number 205-861-8
RTECS number GS6000000
UNII
UN number 1403
Properties
CaCN2
Molar mass 80.102 g/mol
Appearance White solid (Often gray or black from impurities)
Odor odorless
Density 2.29 g/cm3
Melting point 1,340 °C (2,440 °F; 1,610 K)[1]
Boiling point 1,150 to 1,200 °C (2,100 to 2,190 °F; 1,420 to 1,470 K) (sublimes)
Reacts
Hazards
Safety data sheet ICSC 1639
Harmful (Xn)
Irritant (Xi)
R-phrases (outdated) R22 R37 R41
S-phrases (outdated) (S2) S22 S26 S36/37/39
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calciumSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
0
3
1
Flash point Non-flammable
US health exposure limits (NIOSH):
PEL (Permissible)
none[2]
REL (Recommended)
TWA 0.5 mg/m3
IDLH (Immediate danger)
N.D.[2]
Related compounds
Related compounds
Cyanamide
Calcium carbide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
No verify (what is YesYNo ?)
Infobox references

Calcium cyanamide is the inorganic compound with the formula CaCN2. It is the calcium salt of the cyanamide (CN22−) anion. This chemical is used as fertilizer[3] and is commercially known as nitrolime. It was first synthesized in 1898 by Adolph Frank and Nikodem Caro (Frank-Caro process).[4]

History[edit]

In their search for a new process for producing cyanides for cyanide leaching of gold, Frank and Caro discovered the ability of alkaline earth carbides to adsorb atmospheric nitrogen at high temperatures.[5] Fritz Rothe, a colleague of Frank and Caro, succeeded in 1898 in overcoming problems with the use of calcium carbide and clarified that at around 1100 °C not calcium cyanide but calcium cyanamide is formed in the reaction. In fact, the initial target product sodium cyanide can also be obtained from calcium cyanamide by melting it with sodium chloride in the presence of carbon:[6]

Frank and Caro developed this reaction to a large-scale, continuous production process. The process was particularly challenging due to the equipment requirements required by the high temperatures during the initial igniter step. In 1901, Ferdinand Eduard Polzeniusz patented a process that converts calcium carbide to calcium cyanamide in the presence of 10% calcium chloride at 700 °C. The advantage a reaction temperature lowered by about 400 °C, however, is put into perspective by the high amount of calcium chloride required and the discontinuous process control. Nevertheless, both processes (the Rothe-Frank-Caro process and the Polzeniusz-Krauss process) played a role in the first half of the 20th century. In the record year 1945, a total of approx. 1.5 million tonnes were produced worldwide using both processes.[7] Frank and Caro also noted the formation of ammonia from calcium cyanamide.[8]

Albert Frank recognized the fundamental importance of this reaction as a breakthrough in the provision of ammonia from atmospheric nitrogen and recommended in 1901 calcium cyanamide as a nitrogen fertilizer. Between 1908 and 1919, five calcium cyanamide plants with a total capacity of 500,000 tonnes per year were set up in Germany, since calcium cyanamide, which was at the time the cheapest nitrogen fertilizer with additional efficacy against weeds and plant pests, had great advantages over conventional nitrogen fertilizers. However, the large-scale implementation of ammonia synthesis via the Haber–Bosch process caused the very energy-intensive Frank Caro process soon serious competition. As urea (formed via the Haber–Bosch process) was significantly more nitrogen-rich (46% compared to approx. 20% N content) cheaper and faster effective, the role of calcium cyanamide was gradually reduced to a multifunctional nitrogen fertilizer in niche applications. The significant loss of popularity of calcium cyanamide was not only caused by its dirty-black color, dusty appearance and irritating properties, but as well by its characteristic to inhibit in the human body an alcohol-degrading enzyme, so that temporal nearby consumption of alcohol caused a temporary accumulation of acetaldehyde in the body and lead thus to dizziness, nausea and hot flashes.

Production[edit]

Calcium cyanamide is prepared from calcium carbide. The carbide powder is heated at about 1,000 °C in an electric furnace into which nitrogen is passed for several hours.[9] The product is cooled to ambient temperatures and any unreacted carbide is leached out cautiously with water.

CaC2 + N2 → CaCN2 + C (ΔHƒ°= –69.0 kcal/mol at 25 °C)

It crystallizes in hexagonal crystal system with space group R3m and lattice constants a = 3.67, c = 14.85 (.10−1 nm).[10][11]

Uses[edit]

Transformation of calcium cyanamide.svg

The main use of calcium cyanamide is in agriculture as a fertilizer.[3] In contact with water, it decomposes and liberates ammonia:

CaCN2 + 3 H2O → 2 NH3 + CaCO3

It was used to produce sodium cyanide by fusing with sodium carbonate:

CaCN2 + Na2CO3 + 2C → 2 NaCN + CaO + 2CO

Sodium cyanide is used in cyanide process in gold mining. It can also be used in the preparation of calcium cyanide and melamine.

Through hydrolysis in the presence of carbon dioxide, calcium cyanamide produces cyanamide:[clarification needed]

CaCN2 + H2O + CO2 → CaCO3 + H2NCN

The conversion is conducted in slurries, consequently most commercial calcium cyanamide is sold as an aqueous solution.

Thiourea can be produced by the reaction of hydrogen sulfide with calcium cyanamide in the presence of carbon dioxide.[12]

Calcium cyanamide is also used as a wire-fed alloy in steelmaking, in order to introduce nitrogen into the steel.

Safety[edit]

The substance can cause alcohol intolerance, before or after the consumption of alcohol.[13]

References[edit]

  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ a b "NIOSH Pocket Guide to Chemical Hazards #0091". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ a b Auchmoody, L.R.; Wendel, G.W. (1973). "Effect of calcium cyanamide on growth and nutrition of plan fed yellow-poplar seedlings". U.S. Department of Agriculture, Forest Service. Retrieved 2008-07-18. 
  4. ^ "History of Degussa: Rich harvest, healthy environment". Retrieved 2008-07-18. 
  5. ^ Deutsches Reichspatent DRP 88363, „Verfahren zur Darstellung von Cyanverbindungen aus Carbiden“, Erfinder: A. Frank, N. Caro, erteilt am 31. März 1895.
  6. ^ H.H. Franck, W. Burg, Zeitschrift für Elektrochemie und angewandte physikalische Chemie, 40(10), 686-692 (Oktober 1934).
  7. ^ ACS Chemical Landmarks 1998, "Discovery of the commercial processes for making calcium carbide and acetylene"
  8. ^ Angewandte Chemie, Band 29, Ausgabe 16, Seite R97, 25. Februar 1916
  9. ^ Thomas Güthner; Bernd Mertschenk (2006). "Cyanamides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_139.pub2. 
  10. ^ F. Brezina, J. Mollin, R. Pastorek, Z. Sindelar. Chemicke tabulky anorganickych sloucenin (Chemical tables of inorganic compounds). SNTL, 1986.
  11. ^ Vannerberg, N.G. "The crystal structure of calcium cyanamide" Acta Chemica Scandinavica (1-27,1973-42,1988) (1962) 16, p2263-p2266
  12. ^ Mertschenk, Bernd; Beck, Ferdinand; Bauer, Wolfgang (2000). "Thiourea and Thiourea Derivatives". doi:10.1002/14356007.a26_803. 
  13. ^ Potential risks to human health and the environment from the use of calcium cyanamide as fertiliser, Scientific Committee on Health and Environmental Risks, PDF, 1,534 Kb, March 2016, Retrieved 22 July 2017

External links[edit]