Cobalt(II) thiocyanate is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemi ...
with the formula Co(SCN)
2.
It is a layered
coordination complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...
and its trihydrate Co(SCN)
2(H
2O)
3 is used in the cobalt thiocyanate test (or Scott test) for detecting
cocaine
Cocaine (from , from , ultimately from Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly used recreationally for its euphoric effects. It is primarily obtained from the leaves of two Coca species native to South Am ...
. The test has been responsible for widespread false positives and false convictions.
Structure and preparation
left, 259x259px, Structure of Co(SCN)2(H2O)3.
The structures of Co(SCN)
2 and its hydrate Co(SCN)
2(H
2O)
3 have been determined using
X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...
.
Co(SCN)
2 forms infinite 2D sheets in the
mercury(II) thiocyanate
Mercury(II) thiocyanate (Hg(SCN)2) is an inorganic chemical compound, the coordination complex of Hg2+ and the thiocyanate anion. It is a white powder. It will produce a large, winding "snake" when ignited, an effect known as the Pharaoh's serpe ...
structure type, where as Co(SCN)
2(H
2O)
3 consists of isolated tetrahedral Co(SCN)
2(H
2O)
2 centers and one equivalent of
water of crystallization
In chemistry, water(s) of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization is ...
.
[
The hydrate may be prepared by the ]salt metathesis
A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding a ...
reactions, such as the reaction of aqueous cobalt(II) sulfate
Cobalt(II) sulfate is any of the inorganic compounds with the formula CoSO4(H2O)x. Usually cobalt sulfate refers to the hexa- or heptahydrates CoSO4.6H2O or CoSO4.7H2O, respectively. The heptahydrate is a red solid that is soluble in water and ...
and barium thiocyanate
Barium thiocyanate is a colorless water-soluble salt that is very hygroscopic. It is highly toxic to ingestion and irritates the skin. It is also soluble in most alcohols and insoluble in simple alkanes.
Uses
Barium thiocyanate is used in dyeing ...
to produce a barium sulfate
Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium ...
precipitate, leaving the hydrate of Co(SCN)2 in solution:potassium thiocyanate
Potassium thiocyanate is the chemical compound with the molecular formula KSCN. It is an important salt of the thiocyanate anion, one of the pseudohalides. The compound has a low melting point relative to most other inorganic salts.
Use in ch ...
, precipitating KBF4
: o(NCMe)6BF4)2 + 2KSCN → 2KBF4 + Co(SCN)2.
The anhydrate can then be prepared via addition of diethylether
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...
as an antisolvent.
Cobalt thiocyanate test
Detailed procedures for the cobalt thiocyanate test are available. The reagent consists of 2% cobalt thiocyanate dissolved in dilute acid. Glycerol is often added to stabilise the cobalt complex, ensuring it only goes blue when in contact with an analyte and not due to drying.Diphenhydramine
Diphenhydramine (DPH) is an antihistamine and sedative mainly used to treat allergies, insomnia, and symptoms of the common cold. It is also less commonly used for tremor in parkinsonism, and nausea. It is taken by mouth, injected into a v ...
and lidocaine
Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia. When used for local anaesthesia or in nerve blocks, li ...
also give blue organic layers. These compounds are known false positives for cocaine. Lidocaine is commonly used to adulterate or mimic cocaine due to its local anaesthetic effect.
If the procedure is adjusted to basify the sample rather than acidifying it, the test can be used to test for ketamine hydrochloride.
References
{{sulfur compounds
Thiocyanates
Cobalt(II) compounds
Chemical tests
Drug testing reagents
Cocaine