Chemical Properties

Thiocyanic acid, also known as sulfocyanic acid, is a colourless, volatile, strongly odorous acidic liquid. M.p. -110°C. Polymerizes between -90 and -85°C to a white crystalline mass. Converts with careful heating in vacuum to bright-yellow, ether-soluble thiocyanuric acid [(HNCS)3], which readily dissocates into HNCS. If either HNCS or the yellow form is heated at room temperature without evacuation, the material slowly turns dark red, both in the presence and in the absence of air. At about +3°C, a rapid exothermic reaction occurs. The entire mass foams and coalesces into a slurry. Miscible with water in all proportions. Dilute solutions (<5%) are stable. Very strong acid.

Uses

Thiocyanic acid can be used to prepare thiocyanates, esters, various thiocyanates, and cyanides. SCN ions are excellent ligands. A particularly sensitive reaction of SCN ions is the formation of various red complexes with Fe. Therefore, potassium thiocyanate or ammonium thiocyanate are commonly used as reagents for testing for Fe.

Definition

ChEBI: Thiocyanic acid is a hydracid that is cyanic acid in which the oxygen is replaced by a sulfur atom. It has a role as an Escherichia coli metabolite. It is a hydracid, a one-carbon compound and an organosulfur compound. It is a conjugate acid of a thiocyanate. It is a tautomer of an isothiocyanic acid.

Definition

thiocyanic acid: An unstable gas, HSCN.

Synthesis

A mixture of KNCS and KHSO4 is ground together as finely as possible and allowed to stand for 3-4 weeks over P3OS. Then flask a of an apparatus is successively charged (the order of addition should be maintained) with 250 g. of glass beads (6-7 mm. in diameter), 100 g. of KNCS alternated with beads, then a covering layer of glass beads, then the required amount of KHSO4 mixed with glass beads. Without disturbing these layers, the glass flask is mounted in a rigid support and joined on one side of the horizontal tube p via a ground glass spray trap / . The other ground glass joint of a is closed off with a cap.
KNCS + KHSO4 = K2SO4 + HNCS

References

[1] ELLIS M. Chemistry and Biochemistry of Thiocyanic Acid and its Derivatives[J]. Biochemical Society transactions, 1976, 4 1: 540-541. DOI:10.1042/BST0040540.

Raw materials

Preparation Products