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 ...

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 as ...

, which exists as a tautomer with isothiocyanic acid (). The isothiocyanic acid tautomer tends to dominate with the compound 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. One of the thiocyanic acid tautomers, HSCN, is predicted to have a triple bond between

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

and

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

. Thiocyanic acid has been observed spectroscopically. The salts and

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s of thiocyanic acid are known as thiocyanates. The salts are composed of the thiocyanate ion () and a suitable 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. Uses Ch ...

, KSCN). The esters of thiocyanic acid have the general structure , where R stands for an organyl group. 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.< HNCS acceptor properties are discussed in the ECW model. The salts are composed of the thiocyanate ion () and a suitable cation (e.g., ammonium thiocyanate, ). Isothiocyanic acid forms isothiocyanates , where R stands for an organyl group. Thiocyanuric acid is a stable trimer of thiocyanic acid.

References

{{sulfur compounds Mineral acids Thiocyanates