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).[4] The isothiocyanic acid tautomer tends to dominate with the compound being about 95% isothiocyanic acid in the vapor phase.[5]
Names | |
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IUPAC name
Thiocyanic acid[2]
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Other names | |
Identifiers | |
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3D model (JSmol)
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3DMet |
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ChEBI |
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ChEMBL |
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ChemSpider |
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ECHA InfoCard | 100.006.672 |
EC Number |
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25178 | |
KEGG |
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MeSH | thiocyanic+acid |
PubChem CID
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UNII |
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CompTox Dashboard (EPA)
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Properties | |
HSCN | |
Molar mass | 59.09 g·mol−1 |
Appearance | Colorless oily liquid, white or colourless gas, white solid[2] |
Odor | Pungent |
Density | 2.04 g/cm3 |
Melting point | 5 °C (41 °F; 278 K) [2] |
Miscible | |
Solubility | Soluble in ethanol, diethyl ether |
log P | 0.429 |
Vapor pressure | 4.73 mmHg (631 Pa)[2] |
Acidity (pKa) | 0.926 |
Basicity (pKb) | 13.071 |
Hazards | |
GHS labelling: | |
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
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
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It is a moderately strong acid,[6] with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength.[7]
One of the thiocyanic acid tautomers, HSCN, is predicted to have a triple bond between carbon and nitrogen. Thiocyanic acid has been observed spectroscopically.[8]
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.[9] 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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