Cobalt(II) thiocyanate

Cobalt(II) thiocyanate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.019.234
EC Number 221-156-8
Properties
C2CoN2S2
Molar mass 175.098 g/mol
+11,090·10−6 cm3/mol
Hazards
Safety data sheet External MSDS
Xn 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R-phrases (outdated) R20 R21 R22 R32 R50 R53
S-phrases (outdated) S13 S60 S61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).
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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

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

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.

If the procedure is adjusted to basify the sample rather than acidifying it, the test can be used to test for ketamine hydrochloride.[5]

References

  1. ↑ Ryan Gabrielson and Topher Sanders, ProPublica (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?".
  2. ↑ by Ryan Gabrielson, ProPublica (July 11, 2016). "'No Field Test is Fail Safe': Meet the Chemist Behind Houston's Police Drug Kits, Decades after L.J. Scott developed a test for cocaine, his invention played a role in hundreds of wrongful convictions in Houston".
  3. 1 2 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. ↑ Anna L. Deakin (2003). "A Study of Acids Used for the Acidified Cobalt Thiocyanate Test for Cocaine Base". Microgram Journal. 1: 40–43.
  5. ↑ Morris, JA (2007-01-01). "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. Retrieved 2012-02-07.
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