Cobalt(II) thiocyanate

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Cobalt(II) thiocyanate
3D model (JSmol)
ECHA InfoCard 100.019.234
EC Number 221-156-8
Molar mass 175.098 g/mol
+11,090·10−6 cm3/mol
Safety data sheet External MSDS
Harmful Xn Dangerous for the Environment (Nature) N
R-phrases (outdated) R20 R21 R22 R32 R50 R53
S-phrases (outdated) S13 S60 S61
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is ☑Y☒N ?)
Infobox references

Cobalt(II) thiocyanate is an inorganic compound with the formula Co(SCN)2(H2O)3. It is a coordination complex that is used in the cobalt thiocyanate test (or Scott test) for detecting cocaine. The test has been responsible for widespread false positives and false convictions.[1][2]

Structure and preparation[edit]

According to X-ray crystallography, Co(SCN)2(H2O)3 consists of isolated Co(SCN)2(H2O)2 centers and one equivalent of water of crystallization.[3]

This compound may be prepared by the salt metathesis reaction of aqueous cobalt(II) sulfate and barium thiocyanate; barium sulfate precipitates, leaving the hydrate of Co(SCN)2 in solution:[3]

CoSO4 + Ba(SCN)2 → BaSO4 + Co(SCN)2

Cobalt thiocyanate test[edit]

Detailed procedures for the cobalt thiocyanate test are available.[4])

Addition of the cobalt thiocyanate reagent to cocaine hydrochloride results in the surface of the particles turning a bright blue (faint blue for cocaine base). The solution changes back to pink upon adding some hydrochloric acid. Addition of chloroform, results in a blue organic layer for both cocaine hydrochloride and cocaine base. Diphenhydramine and lidocaine 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.[5]


  1. ^ Ryan Gabrielson; Topher Sanders (July 7, 2016). "Busted: Tens of thousands of people every year are sent to jail based on the results of a $2 roadside drug test. Widespread evidence shows that these tests routinely produce false positives. Why are police departments and prosecutors still using them?". ProPublica.
  2. ^ Ryan Gabrielson (July 11, 2016). "'No Field Test is Fail Safe': Meet the Chemist Behind Houston's Police Drug Kits". ProPublica.
  3. ^ a b Cano, F. H.; García-Blanco, S.; Laverat, A. G. (1976). "The crystal structure of cobalt(II) thiocyanate trihydrate". Acta Crystallographica Section B. 32 (5): 1526. doi:10.1107/S0567740876005694.
  4. ^ Deakin, Anna (2003). "A Study of Acids Used for the Acidified Cobalt Thiocyanate Test for Cocaine Base" (PDF). Microgram Journal. 1 (1–2): 40–43. Archived from the original (PDF) on 16 March 2019.
  5. ^ Morris, JA (2007). "Modified Cobalt Thiocyanate Presumptive Color Test for Ketamine Hydrochloride". J Forensic Sci. 52 (1): 84–87. doi:10.1111/j.1556-4029.2006.00331.x. PMID 17209915.