Thiocyanic acid

Structural formula
General
Surname	Thiocyanic acid
other names	Hydrogenthione cyanide; Rhodanic acid; Rhodanic acid; Sulfocyanic acid;
Molecular formula	HSCN
Brief description	oily, colorless liquid with a pungent odor
External identifiers / databases
EC number	207-337-4
ECHA InfoCard	100.006.672
PubChem	781
ChemSpider	760
Wikidata	Q25792
properties
Molar mass	59.09 g mol −1
Physical state	liquid
Melting point	5 ° C
solubility	easily soluble in water; soluble in ethanol and diethyl ether ;
safety instructions
GHS hazard labeling from Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary Caution
H and P phrases	H: 332-312-302-412
	EUH: 032
	P: no P-phrases
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Thiocyanic acid (outdated: hydrofluoric acid ) is an unstable chemical compound with the empirical formula HSCN. It is the sulfur analogon of cyanuric acid HOCN. Their salts and esters are called thiocyanates .

presentation

The preparation of thiocyanic acid can be prepared by reaction of hydrogen sulfide with cyanide mercury (II) take place. Aqueous solutions of the acid are conveniently prepared by decomposing an aqueous solution of ammonium thiocyanate with dilute sulfuric acid . The reaction of barium thiocyanate with dilute sulfuric acid is even better , since this removes the sparingly soluble barium sulfate from the equilibrium and only the thiocyanic acid remains in solution.

{\ displaystyle \ mathrm {2 \ NH_ {4} SCN + H_ {2} SO_ {4} \ longrightarrow 2 \ HSCN + (NH_ {4}) _ {2} SO_ {4}}}

{\ displaystyle \ mathrm {Ba (SCN) _ {2} + H_ {2} SO_ {4} \ longrightarrow 2 \ HSCN + BaSO_ {4} \ downarrow}}

properties

Thiocyanic acid is a colorless volatile compound that has a melting point of 5 ° C. It is readily soluble in water and a few organic solvents . Thiocyanic acid is unstable and only stable at low temperatures. Aqueous solutions are resistant up to 5% HSCN content and form a very strong acid. Higher concentrations produce hydrogen cyanide and perthiocyanic acid as decomposition products . Thiocyanic acid (left) is in a tautomeric equilibrium with isothiocyanic acid (right), with the equilibrium on the left, i.e. with thiocyanic acid:

Furthermore, there is thiazirine (a sulfur derivative of azirine ), a heterocyclic thiocyanic acid isomer , which can occur as an intermediate:

Individual evidence

↑ ^a ^b ^c ^d ^e Entry on thiocyanic acid. In: Römpp Online . Georg Thieme Verlag, accessed on September 29, 2014.
↑ ^a ^b ^c ^d ^e Entry on hydrofluoric acid in the GESTIS substance database of the IFA , accessed on February 21, 2017(JavaScript required) .
^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 1413.
↑ Entry on thiocyanic acid 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 .
↑ Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , p. 637.

[roempp-1] Entry on thiocyanic acid. In: Römpp Online . Georg Thieme Verlag, accessed on September 29, 2014.

[GESTIS-2] Entry on hydrofluoric acid in the GESTIS substance database of the IFA , accessed on February 21, 2017(JavaScript required) .

[ABC_Chemie-3] Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 1413.

[CLP_100.006.672-4] Entry on thiocyanic acid 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 .

[brauer-5] Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , p. 637.