Cyanamide

Structural formula
General
Surname	Cyanamide
other names	Alzodef Amidocyanogen Carbamic acid nitrile Carbamonitrile Carbodiimide Cyanogenamide Cyanamide Defolup Hydrogen cyanamide Carbonitrile Carbodiimide
Molecular formula	CH 2 N 2
Brief description	colorless, hygroscopic solid
External identifiers / databases
CAS number 420-04-2 EC number 206-992-3 ECHA InfoCard 100.006.358 PubChem 9864 ChemSpider 9480 DrugBank DB02679 Wikidata Q414555
properties
Molar mass	42.0 g mol −1
Physical state	firmly
density	1.282 g cm −3 (20 ° C)
Melting point	44 ° C
boiling point	260 ° C (decomposition)
solubility	easily in water (775 g l −1 ) easily in ethanol , diethyl ether and many polar organic solvents
Refractive index	1.4418 (48 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 301-311-314-317-351-361fd-373-412 P: 260-273-280-301 + 330 + 331-303 + 361 + 353-305 + 351 + 338-310-405
MAK	DFG : 0.2 ml m −3 or 0.35 mg m −3 Switzerland: 0.58 ml m −3 or 1 mg m −3
Toxicological data	125 mg kg −1 ( LD 50 ,  rat ,  oral )
Thermodynamic properties
ΔH f 0	58.8 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Cyanamide is the amide of cyanic acid . It can also be understood as the nitrile of carbamic acid and, in its equilibrium form, carbodiimide, also as the diimide of carbon dioxide .

Extraction and presentation

Scheme of a cyanamide plant

Cyanamide can be prepared by hydrolysis of the Frank-Caro method shown Calciumcyanamids (also cyanamide ) in the presence of carbon dioxide are prepared:

${\displaystyle \mathrm {CaCN_{2}+H_{2}O+CO_{2}\ \rightarrow \ H_{2}NCN+CaCO_{3}} }$

If cyanogen chloride is allowed to react with ammonia , cyanamide is also formed, which is in equilibrium with carbodiimide.

${\displaystyle \mathrm {Cl{-}C{\equiv }N\ +\ NH_{3}\ {\xrightarrow {-HCl}}\ } }$ ${\displaystyle \mathrm {\ H_{2}N{-}C{\equiv }N\ \rightleftharpoons \ HN{=}C{=}NH} }$

properties

Cyanamide is a colorless, odorless, crystalline, hygroscopic substance with a very high reactivity, which polymerizes in part explosively when heated. The toxic substance is flammable and readily soluble in water (850 g · l ⁻¹ at 25 ° C) and organic solvents. The 50% aqueous solution, which is colored blue as a commercial form, has an acidic reaction ( pH value 3.5–4.2 at a concentration of 560 g · l ⁻¹ at 20 ° C).

use

Since the mid-1960s there have been processes for stabilizing cyanamide and making it available on an industrial scale. Because of the strong tendency to self-condensation (dimer: dicyandiamide , trimer: melamine ) in an alkaline environment, cyanamide solutions are stabilized by adding 0.5% by weight of NaH ₂ PO ₄ phosphate buffer. Stable solid cyanamide is produced by carefully evaporating a stabilized cyanamide solution and then adding a hydrolysis-labile formic acid ester, which absorbs traces of moisture (suppresses urea formation), neutralizes traces of alkali (ammonia) and continuously releases small amounts of formic acid.

In agriculture, cyanamide is used as a fertilizer and as a plant growth regulator by breaking the dormancy of fruit plants (table grapes, kiwis, apples, pears) ( dormancy breaking agent ). The 50% aqueous solution is also used as a biocide ( disinfectant ), particularly in pig breeding, as it effectively kills salmonella and dysentery bacteria and combats flies in all stages of development.

In the chemical industry , cyanamide is used as a diverse starting material, e.g. B. for the production of herbicides , synthetic resins (hardening of epoxides) and as a bleach activator for hydrogen peroxide at alkaline pH in detergents and for chlorine-free pulp bleaching. Most of the cyanamide is immediately converted to cyanoguanidine and processed further.

Cyanamide can be viewed as a functional monocarbon fragment that can react as an electrophile or nucleophile . The cyanamide anion has the character of a pseudochalcogenide . Therefore, cyanamide can be viewed as an analogue to water or hydrogen sulfide. A convenient method of preparing secondary amines that are not contaminated with primary or tertiary amines is to react cyanamide with alkyl halides to give N , N -dialkylcyanamides, which are easily hydrolyzed and decarboxylated to dialkylamines . In the presence of N- bromo succinimide NBS, cyanamide adds to olefinic double bonds. The addition product is converted into N- cyanoaziridines by bases , cyclized in the presence of acids to imidazolines , from which vicinal diamines can be prepared by alkaline cleavage .

Cyanamide is also suitable as a versatile synthetic building block for heterocycles: 1,2-diaminobenzene ( o -phenylenediamine) forms 2-aminobenzimidazole, with the easily accessible cyclic enamine 4- (1-cyclohexenyl) morpholine and elemental sulfur a 2-aminothiazole in good yields . Sodium dicyanamide can be obtained in good yield and high purity from cyanamide and cyanogen chloride and is suitable as an intermediate for the synthesis of active pharmaceutical ingredients.

In the industrial synthesis of creatine , which is essential for muscle, nerve and brain function , the guanidine residue is introduced through the reaction of cyanamide with sarcosine .

This synthesis route largely avoids problematic contamination with chloroacetic acid, iminodiacetic acid or dihydrotriazine, which occur with other routes. Similarly, the physiological precursor guanidinoacetic acid is obtained by reacting cyanamide with glycine .

Admission

No plant protection products with the active ingredient cyanamide are permitted in the EU . Nevertheless, cyanamide can be manufactured in the EU for export . The active ingredient manufactured by BASF is still sold on the Brazilian market.

Derived connections

• Calcium cyanamide (artificial fertilizer)
• melamine
• Dicyandiamide
• urea
• Thiourea
• Guanidines
• Carbodiimides RN = C = NR ′
• Dicyanamine HN (CN) ₂

safety instructions

Cyanamide is a contact poison that can exert its effects through absorption through the skin. Uptake via the respiratory tract is unlikely due to the hygroscopic character and low vapor pressure of the substance. Absorption via the stomach and digestive tract is rapid but incomplete. There are individual case reports of the occurrence of acetaldehyde syndrome after skin contact with fertilizers containing cyanamide and previous consumption of alcohol.

Individual evidence

1. ↑ ^{a b} entry on cyanamide. In: Römpp Online . Georg Thieme Verlag, accessed on October 14, 2014.
2. ↑ ^{a b c d e f g h i j} Entry on cyanamide in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-124.
4. ↑ Entry on cyanamides 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 .
5. ↑ Cyanamide data sheet at Sigma-Aldrich , accessed on February 4, 2018 ( PDF ).
6. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 420-04-2 or cyanamide ), accessed on November 2, 2015.
7. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-19.
8. ↑ Wehrstedt, K.-D .; Wildner, W .; Güthner, T .; Holzrichter, K .; Mertschenk, B .; Ulrich, A .: Safe transport of cyanamide in J. Hazard. Mat. 170 (2009) 829-835, doi : 10.1016 / j.jhazmat.2009.05.043 .
9. ↑ AlzChem: ALZOGUR .
10. ↑ European patent application EP-A-0 479 319, applicant: SKW Trostberg AG, filed on October 4, 1991.
11. ↑ Jonczyk, A .; Ochal, Z .; Makosza, M .: Reactions of Organic Anions; LXXXV1. Catalytic Two-Phase Alkylation of Cyanamide in Synthesis , 1978, 882-883, doi : 10.1055 / s-1978-24922 .
12. ^ Ponsold, K .; Ihn, W .: The addition of cyanamide and halogen to olefins a new process for the preparation of vic.-halocyanamines and aziridines in Tetrahedron Lett. 11 (1970) 1125-1128, doi : 10.1016 / S0040-4039 (01) 97925-0 .
13. ↑ Harold Kohn, Sang Hun Jung: New stereoselective method for the preparation of vicinal diamines from olefins and cyanamide. In: Journal of the American Chemical Society. 105, 1983, pp. 4106-4108, doi : 10.1021 / ja00350a068 .
14. ↑ Stefan Weiss, Horst Michaud, Horst Prietzel, Helmut Krommer: A New, Simple Synthesis of 2-Aminobenzimidazole. In: Angewandte Chemie International Edition in English. 12, 1973, p. 841, doi : 10.1002 / anie.197308411 .
15. ^ S. Hünig, E. Lücke, and W. Brenninger: 1-Morpholino-1-Cyclohexene In: Organic Syntheses . 41, 1961, p. 65, doi : 10.15227 / orgsyn.041.0065 ; Coll. Vol. 5, 1973, p. 808 ( PDF ).
16. ↑ K. Gewald, H. Spies, R. Mayer: On the reaction of enamines with sulfur and cyanamide. In: Journal for Practical Chemistry. 312, 1970, p. 776, doi : 10.1002 / prac.19703120507 .
17. ↑ Process for the preparation of sodium dicyanamide , published on August 10, 2000, applicant: SKW Trostberg AG.
18. ↑ Lonza: Sodium dicyanamide ( Memento of the original dated May 23, 2013 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. 
19. ↑ German Offenlegungsschrift DE-OS 10 2006 016 227 A1, publication date: October 11, 2007, applicant: Degussa GmbH.
20. ↑ General Directorate Health and Food Safety of the European Commission: Entry on cyanamides (H & Ca cyanamide) in the EU pesticide database; accessed on October 1, 2019.
21. ↑ Maurin Jost: Export of harmful pesticides: A lot of poison for abroad. In: taz.de . September 29, 2019, accessed October 1, 2019 . 
22. ^ Benjamin Luig, Fran Paula de Castro, Alan Tygel, Lena Luig, Simphiwe Dada, Sarah Schneider, Jan Urhahn: Hazardous pesticides. (PDF; 2.4 MB) from Bayer and BASF - a global business with double standards. Rosa Luxemburg Foundation , INKOTA network , Bischöfliches Hilfswerk Misereor , Campanha Permanente Contra os Agrotóxicos e Pela Vida, Khanyisa, April 2020, accessed on April 25, 2020 . 
23. ↑ L. de Haro: Disulfiram-like syndrome after hydrogen cyanamide professional skin exposure: two case reports in France. In: Journal of agromedicine. Volume 14, Number 3, 2009, pp. 382-384, ISSN  1545-0813 . doi : 10.1080 / 10599240903050704 . PMID 19657887 .