Chemical Properties
White substance with an enamel luster. 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: A hydracid that is cyanic acid in which the oxygen is replaced by a sulfur atom.
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.
