Thiocyanic acid is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

HSCN and

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...

, which exists as a

tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hy ...

with isothiocyanic acid (HNCS). The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase. : Thiocyanic Acid Tautomerism V

It is a moderately strong acid, with a p''K''_a of 1.1 at 20 °C and extrapolated to zero ionic strength. HSCN is predicted to have a

triple bond A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order o ...

between carbon and nitrogen. It has been observed spectroscopically but has not been isolated as a pure substance. The

salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...

and

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

s of thiocyanic acid are known as

thiocyanate Thiocyanate (also known as rhodanide) is the anion . It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyr ...

s. The salts are composed of the thiocyanate ion (⁻SCN) and a suitable metal cation (e.g.,

potassium thiocyanate Potassium thiocyanate is the chemical compound with the molecular formula KSCN. It is an important salt of the thiocyanate anion, one of the pseudohalides. The compound has a low melting point relative to most other inorganic salts. Use in che ...

, KSCN). The esters of thiocyanic acid have the general structure R–SCN. Isothiocyanic acid, HNCS, is a Lewis acid whose free energy, enthalpy and entropy changes for its 1:1 association with a variety of Lewis bases in carbon tetrachloride solution at 25 °C have been reported.. Barakat, T. M.; Nelson, J.; Nelson, S. M.; Pullin, A. D. E. (1969.) “Spectra and hydrogen-bonding of characteristics of thiocyanic acid. Part 4.—Association with weak proton acceptors”. Trans. Faraday Soc., 1969,65, 41-51 HNCS acceptor properties are discussed in the ECW model.

References

{{sulfur compounds Mineral acids Thiocyanates