Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chemical compound
Thiocyanic acid is a chemical compound with the formula HSCN 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]
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.
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^Merck Index, 11th Edition, 9257.
^ ab"Thiocyanic acid". The Merck Index. Royal Society of Chemistry.
^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.
^"Thiocyanic acid" entry in PubChem (database).
^ abILO and WHO staff. "Thiocyanic acid" safety card. European Commission
^Birckenbach, Lothar (1942). Forschungen und Fortschritte. 18: 232–3 {{cite journal}}: Missing or empty |title= (help). As cited in CAS Common Chemistry.
^Brown, Jay A. (ed.; 2024), "Thiocyanic Acid" in Haz-Map (database). Engineered IT.
^Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
^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.
^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.
^Martell, A. E.; Smith, R. M.; Motelaitis, R. J. (2001). NIST Database 46. Gaithersburg, MD: National Institute of Standards and Technology.
^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.
^. 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
Thiocyanicacid is a chemical compound with the formula HSCN and structure H−S−C≡N, which exists as a tautomer with isothiocyanic acid (H−N=C=S). The isothiocyanic...
esters of thiocyanicacid and trithiocarbonic acid). An example of an ester formation is the substitution reaction between a carboxylic acid (R−C(=O)−OH)...
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easily dissolves in water, posing a health risk to the lungs. Cyanate Thiocyanicacid Cyanamide also has this name, and for which it is more systematically...
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which quickly hydrates to sulfuric acid: H2S + 2 O2 → H2SO4 It is slightly soluble in water and acts as a weak acid (pKa = 6.9 in 0.01–0.1 mol/litre solutions...
sulfuric acid. SO2 + H2O + 1⁄2 O2 → H2SO4 Sulfur dioxide dissolves in water to give "sulfurous acid", which cannot be isolated and is instead an acidic solution...
Methyl acetate, also known as MeOAc, acetic acid methyl ester or methyl ethanoate, is a carboxylate ester with the formula CH3COOCH3. It is a flammable...
compound with the formula [NH4]+[SCN]−. It is an ammonium salt of thiocyanicacid. It consists of ammonium cations [NH4]+ and thiocyanate anions [SCN]−...
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reaction with alcohols, carboxylic acid esters are formed: Ketenes react with a carboxylic acids to form carboxylic acid anhydrides: Ketenes react with ammonia...
reactive compounds. It is typically stored with a stabilizer in a weakly acidic solution in an opaque bottle. Hydrogen peroxide is found in biological systems...
Another method entails reducing nitromethane with zinc and hydrochloric acid. Another method of methylamine production is spontaneous decarboxylation...
including acetamidine hydrochloride, thiamine, and 1-naphthaleneacetic acid. Its reaction with cyanogen chloride affords malononitrile. Acetonitrile...
known as rhodanide or rhodanate). [SCN]− is the conjugate base of thiocyanicacid. Common salts include the colourless salts potassium thiocyanate and...
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When treated with acid, it forms the toxic gas hydrogen cyanide: NaCN + H+ → HCN + Na+ Because the salt is derived from a weak acid, sodium cyanide readily...
produce optically pure methyl compounds, e.g., chiral acetic acid (deuterotritoacetic acid CHDTCO2H). Through the use of chiral methyl groups, the stereochemical...
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solution termed hydrofluoric acid. It is the principal industrial source of fluorine, often in the form of hydrofluoric acid, and is an important feedstock...
products. The O-acylisourea 2 can react with an additional carboxylic acid 1 to give an acid anhydride 5, which can react further to give the amide 3. The main...
carbon atom, like methanol. It is a weak acid, with a pKa of ~10.4, but is about a hundred thousand times more acidic than methanol. The colorless salt can...
cyanic acid and the original cysteine. Cleaving proteins with BrCN requires using a buffer such as 0.1M HCl (hydrochloric acid) or 70% (formic acid). These...