Thiocyanic acid

Last updated
Thiocyanic acid [1]
Thiocyansaure.png
Thiocyanic-acid-3D-vdW.png
   Carbon, C
   Sulfur, S
   Nitrogen, N
   Hydrogen, H
Names
IUPAC name
Thiocyanic acid [2]
Other names
  • Hydrogen thiocyanate [3]
  • Sulfocyanic acid [4]
Identifiers
3D model (JSmol)
3DMet
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.006.672 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 207-337-4
25178
KEGG
MeSH thiocyanic+acid
PubChem CID
UNII
  • InChI=1S/CHNS/c2-1-3/h3H Yes check.svgY
    Key: ZMZDMBWJUHKJPS-UHFFFAOYSA-N Yes check.svgY
  • SC#N
Properties
HSCN
Molar mass 59.09 g·mol−1
Appearance
  • Colourless liquid [5]
  • Colourless gas, autopolymerizing to white solid [3]
Odor Pungent
Density 2.04 g/cm3
Melting point
  • 5 °C (oligomers?) [5]
  • -110 °C (monomer?) [6]
Miscible
Solubility Soluble in ethanol, diethyl ether
log P 0.429
Vapor pressure 4.73 mmHg (631 Pa) [7]
Acidity (pKa)0.926
Basicity (pKb)13.071
Hazards
GHS labelling:
GHS-pictogram-exclam.svg
Warning
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 compounds
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 H S C N and structure H−S−C≡N, which exists as a tautomer with isothiocyanic acid (H−N=C=S). [8] The isothiocyanic acid tautomer tends to dominate with the compound being about 95% isothiocyanic acid in the vapor phase. [9]

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, [10] with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength. [11]

One of the thiocyanic acid tautomers, HSCN, is predicted to have a triple bond between carbon and nitrogen. Thiocyanic acid has been observed spectroscopically. [12]

The salts and esters of thiocyanic acid are known as thiocyanates. The salts are composed of the thiocyanate ion ([SCN]) and a suitable cation (e.g., potassium thiocyanate, KSCN). The esters of thiocyanic acid have the general structure R−S−C≡N, 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. [13] HNCS acceptor properties are discussed in the ECW model. The salts are composed of the thiocyanate ion ([SCN]) and a suitable cation (e.g., ammonium thiocyanate, [NH4]+[SCN]). Isothiocyanic acid forms isothiocyanates R−N=C=S, where R stands for an organyl group.

Related Research Articles

<span class="mw-page-title-main">Carbonate</span> Salt or ester 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 CO2−3. The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate groupO=C(−O−)2.

<span class="mw-page-title-main">Ester</span> Compound derived from an acid

In chemistry, an ester is a compound derived from an acid in which the hydrogen atom (H) of at least one acidic hydroxyl group of that acid is replaced by an organyl group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well, but not according to the IUPAC.

<span class="mw-page-title-main">Organic compound</span> Carbon-containing chemical compound

Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-containing compounds such as alkanes and its derivatives are universally considered organic, but many others are sometimes considered inorganic, such as halides of carbon without carbon-hydrogen and carbon-carbon bonds, and certain compounds of carbon with nitrogen and oxygen.

In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases.

<span class="mw-page-title-main">Acyl group</span> Chemical group (R–C=O)

In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an organyl group or hydrogen in the case of formyl group. In organic chemistry, the acyl group is usually derived from a carboxylic acid, in which case it has the formula R−C(=O)−, where R represents an organyl group or hydrogen. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids and phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond.

<span class="mw-page-title-main">Acetate</span> Salt compound formed from acetic acid and a base

An acetate is a salt formed by the combination of acetic acid with a base. "Acetate" also describes the conjugate base or ion typically found in aqueous solution and written with the chemical formula C
2
H
3
O
2
. The neutral molecules formed by the combination of the acetate ion and a positive ion are also commonly called "acetates". The simplest of these is hydrogen acetate with corresponding salts, esters, and the polyatomic anion CH
3
CO
2
, or CH
3
COO
.

<span class="mw-page-title-main">Isothiocyanate</span> Chemical group (–N=C=S)

In organic chemistry, isothiocyanate is a functional group as found in compounds with the formula R−N=C=S. Isothiocyanates are the more common isomers of thiocyanates, which have the formula R−S−C≡N.

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

Thiocyanates are salts containing the thiocyanate anion [SCN]. [SCN] is the conjugate base of thiocyanic acid. Common salts include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyrotechnics.

<span class="mw-page-title-main">Cyanate</span> Anion with formula OCN and charge –1

The cyanate ion is an anion with the chemical formula OCN. It is a resonance of three forms: [O−C≡N] (61%) ↔ [O=C=N] (30%) ↔ [O+≡C−N2−] (4%).

Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature is abound with organosulfur compounds—sulfur is vital for life. Of the 20 common amino acids, two are organosulfur compounds, and the antibiotics penicillin and sulfa drugs both contain sulfur. While sulfur-containing antibiotics save many lives, sulfur mustard is a deadly chemical warfare agent. Fossil fuels, coal, petroleum, and natural gas, which are derived from ancient organisms, necessarily contain organosulfur compounds, the removal of which is a major focus of oil refineries.

<span class="mw-page-title-main">Xanthate</span> Salt that is a metal-thioate/O-esters of dithiocarbonate

A xanthate is a salt or ester of a xanthic acid. The formula of the salt of xanthic acid is [R−O−CS2]M+. Xanthate also refers to the anion [R−O−CS2]. The formula of a xanthic acid is R−O−C(=S)−S−H, such as ethyl xanthic acid, while the formula of an ester of a xanthic acid is R−O−C(=S)−S−R', where R and R' are organyl groups. The salts of xanthates are also called O-organyl dithioates. The esters of xanthic acid are also called O,S-diorganyl esters of dithiocarbonic acid. The name xanthate is derived from Ancient Greek ξανθός (xanthos) meaning 'yellowish' or 'golden', and indeed most xanthate salts are yellow. They were discovered and named in 1823 by Danish chemist William Christopher Zeise. These organosulfur compounds are important in two areas: the production of cellophane and related polymers from cellulose and for extraction of certain sulphide bearing ores. They are also versatile intermediates in organic synthesis.

<span class="mw-page-title-main">Meldrum's acid</span> Chemical compound

Meldrum's acid or 2,2-dimethyl-1,3-dioxane-4,6-dione is an organic compound with formula C6H8O4. Its molecule has a heterocyclic core with four carbon and two oxygen atoms; the formula can also be written as [−O−(C 2)−O−(C=O)−(CH2)−(C=O)−].

<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 and an isomer of cyanic acid (aka. cyanol).

<span class="mw-page-title-main">Thiosulfate</span> Polyatomic ion (S2O3, charge –2)

Thiosulfate is an oxyanion of sulfur with the chemical formula S2O2−3. Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, e.g. sodium thiosulfate Na2S2O3. Thiosulfate also refers to the esters of thiosulfuric acid. The prefix thio- indicates that the thiosulfate is a sulfate with one oxygen replaced by sulfur. Thiosulfate is tetrahedral at the central S atom. Thiosulfate salts occur naturally. Thiosulfate ion has C3v symmetry, and is produced by certain biochemical processes. It rapidly dechlorinates water and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate salts are mainly used in dying in textiles and the bleaching of natural substances.

<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:

Zinc compounds 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 appearance and behavior: they are generally colorless, do not readily engage in redox reactions, and generally adopt symmetrical structures.

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

Ammonium thiocyanate is an inorganic compound with the formula [NH4]+[SCN]. It is an ammonium salt of thiocyanic acid. It consists of ammonium cations [NH4]+ and thiocyanate anions [SCN].

<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">Organic thiocyanates</span>

Organic thiocyanates are organic compounds containing the functional group RSCN. the organic group is attached to sulfur: R−S−C≡N has a S–C single bond and a C≡N triple bond.

References

  1. Merck Index , 11th Edition, 9257.
  2. "Thiocyanic acid" entry in PubChem (database).
  3. 1 2 "Thiocyanic acid" . The Merck Index . Royal Society of Chemistry.
  4. von Richter, Victor (1922). Organic Chemistry or Chemistry of the Carbon Compounds. Vol. 1. Translated by Spielmann, Percy E. Philadelphia: P. Blakiston's Son & Co. p. 466.
  5. 1 2 ILO and WHO staff. "Thiocyanic acid" safety card. European Commission
  6. Birckenbach, Lothar (1942). Forschungen und Fortschritte. 18: 232–3{{cite journal}}: Missing or empty |title= (help). As cited in CAS Common Chemistry.
  7. Brown, Jay A. (ed.; 2024), "Thiocyanic Acid" in Haz-Map (database). Engineered IT.
  8. Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN   0-12-352651-5.
  9. 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 .
  10. 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.
  11. Martell, A. E.; Smith, R. M.; Motelaitis, R. J. (2001). NIST Database 46. Gaithersburg, MD: National Institute of Standards and Technology.
  12. 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.
  13. . 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