Thiocyanic acid

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.

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

Raw materials

Preparation Products