Thiocyanic acid

Last updated
Thiocyanic acid [1]
Preferred IUPAC name
Thiocyanic acid [2]
Other names
3D model (JSmol)
ECHA InfoCard 100.006.672 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 207-337-4
MeSH thiocyanic+acid
PubChem CID
  • InChI=1S/CHNS/c2-1-3/h3H Yes check.svgY
  • SC#N
Molar mass 59.09 g·mol−1
Appearancecolorless, oily liquid
Odor pungent
Density 2.04 g/cm3
Melting point 5 °C (41 °F; 278 K)
Solubility soluble in ethanol, diethyl ether
log P 0.429
Acidity (pKa)0.926
Basicity (pKb)13.071
GHS labelling:
H302, H312, H332, H412
P261, P264, P270, P271, P273, P280, P301+P312, P302+P352, P304+P312, P304+P340, P312, P322, P330, P363, P501
Related compounds
Related alkanenitriles
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Thiocyanic acid is a chemical compound with the formula HSCN and structure H−S−C≡N, which exists as a tautomer with isothiocyanic acid (HNCS). [4] The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase. [5]

Tautomerism between thiocyanic acid (left) and isothiocyanic acid (right) Thiocyanic Acid Tautomerism V.1.svg
Tautomerism between thiocyanic acid (left) and isothiocyanic acid (right)

It is a moderately strong acid, [6] with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength. [7]

HSCN is predicted to have a triple bond between carbon and nitrogen. It has been observed spectroscopically but has not been isolated as a pure substance. [8]

The salts and esters of thiocyanic acid are known as thiocyanates. The salts are composed of the thiocyanate ion (SCN) and a suitable metal cation (e.g., potassium thiocyanate, 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. [9] HNCS acceptor properties are discussed in the ECW model.

Related Research Articles

<span class="mw-page-title-main">Carbonate</span> Salt of carbonic acid

A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−
. The word carbonate may also refer to a carbonate ester, an organic compound containing the carbonate group C(=O)(O–)2.

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Nitrogen</span> Chemical element, symbol N and atomic number 7

Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bind to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids (DNA and RNA) and in the energy transfer molecule adenosine triphosphate. The human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes the movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere.

<span class="mw-page-title-main">Organic compound</span> Chemical compound with carbon-hydrogen bonds

In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate, millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprise the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds, along with a few other exceptions, are not classified as organic compounds and are considered inorganic. Other than those just named, little consensus exists among chemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive.

In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is not clearly defined; authorities have differing views on the subject. The study of inorganic compounds is a subfield of chemistry known as inorganic chemistry.

<span class="mw-page-title-main">Barium hydroxide</span> Chemical compound

Barium hydroxide is a chemical compound with the chemical formula Ba(OH)2. The monohydrate (x = 1), known as baryta or baryta-water, is one of the principal compounds of barium. This white granular monohydrate is the usual commercial form.

<span class="mw-page-title-main">Thiocyanate</span> Ion (S=C=N, charge –1)

Thiocyanate is the anion [SCN]. 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 pyrotechnics.

In organic chemistry, the Michael reaction or Michael addition describes a reaction between any Michael donor and any Michael acceptor. It belongs to the larger class of conjugate additions and is widely used for the mild formation of C–C bonds. Many asymmetric variants exist and depending on the conditions, Michael Additions can be diastereoselective and/or enantioselective.

<span class="mw-page-title-main">Organoboron chemistry</span> Study of compounds containing a boron-carbon bond

Organoborane or organoboron compounds are chemical compounds of boron and carbon that are organic derivatives of BH3, for example trialkyl boranes. Organoboron chemistry or organoborane chemistry is the chemistry of these compounds.

Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine predominantly in patients experiencing renal failure. A guanidine moiety also appears in larger organic molecules, including on the side chain of arginine.

<span class="mw-page-title-main">Isocyanic acid</span> Chemical compound (H–N=C=O)

Isocyanic acid is a chemical compound with the structural formula HNCO, which is often written as H−N=C=O. It is a colourless, volatile and poisonous substance, with a boiling point of 23.5 °C. It is the predominant tautomer of cyanic acid.

<span class="mw-page-title-main">Mercury(II) thiocyanate</span> Chemical compound

Mercury(II) thiocyanate (Hg(SCN)2) is an inorganic chemical compound, the coordination complex of Hg2+ and the thiocyanate anion. It is a white powder. It will produce a large, winding "snake" when ignited, an effect known as the Pharaoh's serpent.

<span class="mw-page-title-main">Sodium thiocyanate</span> Chemical compound

Sodium thiocyanate (sometimes called sodium sulphocyanide) is the chemical compound with the formula NaSCN. This colorless deliquescent salt is one of the main sources of the thiocyanate anion. As such, it is used as a precursor for the synthesis of pharmaceuticals and other specialty chemicals. Thiocyanate salts are typically prepared by the reaction of cyanide with elemental sulfur:

Bromine compounds are compounds containing the element bromine (Br). These compounds usually form the -1, +1, +3 and +5 oxidation states. Bromine is intermediate in reactivity between chlorine and iodine, and is one of the most reactive elements. Bond energies to bromine tend to be lower than those to chlorine but higher than those to iodine, and bromine is a weaker oxidising agent than chlorine but a stronger one than iodine. This can be seen from the standard electrode potentials of the X2/X couples (F, +2.866 V; Cl, +1.395 V; Br, +1.087 V; I, +0.615 V; At, approximately +0.3 V). Bromination often leads to higher oxidation states than iodination but lower or equal oxidation states to chlorination. Bromine tends to react with compounds including M–M, M–H, or M–C bonds to form M–Br bonds.

Carbamic acid, which might also be called aminoformic acid or aminocarboxylic acid, is the chemical compound with the formula H2NCOOH. It can be obtained by the reaction of ammonia NH3 and carbon dioxide CO2 at very low temperatures, which also yields an equal amount of ammonium carbamate [NH4]+[NH2CO2]. The compound is stable only up to about 250 K (−23 °C); at higher temperatures it decomposes into those two gases. The solid apparently consists of dimers, with the two molecules connected by hydrogen bonds between the two carboxyl groups –COOH.

<span class="mw-page-title-main">Lead(II) thiocyanate</span> Chemical compound

Lead(II) thiocyanate is a compound, more precisely a salt, with the formula Pb(SCN)2. It is a white crystalline solid, but will turn yellow upon exposure to light. It is slightly soluble in water and can be converted to a basic salt (Pb(CNS)2·Pb(OH)2 when boiled. Salt crystals may form upon cooling. Lead thiocyanate can cause lead poisoning if ingested and can adversely react with many substances. It has use in small explosives, matches, and dyeing.

Compounds of zinc are chemical compounds containing the element zinc which is a member of the group 12 of the periodic table. The oxidation state of zinc in most compounds is the group oxidation state of +2. Zinc may be classified as a post-transition main group element with zinc(II). Zinc compounds are noteworthy for their nondescript behavior, they are generally colorless, do not readily engage in redox reactions, and generally adopt symmetrical structures.

<span class="mw-page-title-main">Silver thiocyanate</span> Chemical compound

Silver thiocyanate is the silver salt of thiocyanic acid with the formula AgSCN.

<span class="mw-page-title-main">Copper(I) thiocyanate</span> Chemical compound

Copper(I) thiocyanate is a coordination polymer with formula CuSCN. It is an air-stable, white solid used as a precursor for the preparation of other thiocyanate salts.

<span class="mw-page-title-main">Thorium(IV) nitrate</span> Chemical compound

Thorium(IV) nitrate is a chemical compound with the formula Th(NO3)4. A white solid in its anhydrous form, it can form tetra- and pentahydrates. As a salt of thorium it is weakly radioactive.


  1. Merck Index , 11th Edition, 9257.
  2. International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 784. doi:10.1039/9781849733069. ISBN   978-0-85404-182-4.
  3. Richter, Victor von; Spielmann, Percy E., trans. (1922). Organic Chemistry or Chemistry of the Carbon Compounds. Vol. 1. Philadelphia, Pennsylvania, U.S.A.: P. Blakiston's Son & Co. p. 466.
  4. Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN   0-12-352651-5.
  5. Beard, C. I.; Dailey, B. P. (1950). "The Structure and Dipole Moment of Isothiocyanic Acid" (PDF). The Journal of Chemical Physics . 18 (11): 1437. Bibcode:1950JChPh..18.1437B. doi:10.1063/1.1747507. hdl: 1721.1/4934 .
  6. Munegumi, Toratane (23 January 2013). "Where is the Border Line between Strong Acids and Weak Acids?". World Journal of Chemical Education. 1 (1): 12–16.
  7. Martell, A. E.; Smith, R. M.; Motelaitis, R. J. (2001). NIST Database 46. Gaithersburg, MD: National Institute of Standards and Technology.
  8. Wierzejewska, M.; Mielke, Z. (2001). "Photolysis of Isothiocyanic Acid HNCS in Low-Temperature Matrices. Infrared Detection of HSCN and HSNC Isomers". Chemical Physics Letters . 349 (3–4): 227–234. Bibcode:2001CPL...349..227W. doi:10.1016/S0009-2614(01)01180-0.
  9. . 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