Bis(N,N-diethyl-4-methyl-4-piperazine-1-carboxamide) tetrakis(isothiocyanato-κN)cobalt(II), a model compound for the blue color developed in the Scott test

Abstract

The complex, bis(N,N-diethyl-4-methyl-4-piperazine-1-carboxamide) tetrakis(isothiocyanato-κN)cobalt(II) (N,N-diethyl-4-methyl-4-piperazine-1-carboxamide = diethylcarbamazine), (C10H22N3O)2[Co(NCS)4], is presented. This complex is a blue precipitate, insoluble in water but soluble in organic solvents, that is formed from the reaction of diethylcarbamazine citrate, a protonated tertiary amine, with cobalt(II) and thiocyanate. This reaction, in the form of the Scott test, is a common presumptive test for cocaine hydrochloride. The known cobalt compound, [K2Co(NCS)4]·3H2O, has a deep-blue coloration due to the tetrahedral [Co(NCS)4]2− that is also present in the ion pair with bulky amines, and is similar to the color of other tetrahedral cobalt(II) complex ions, such as [CoCl4]2−. The structure is consistent with a previous proposal that a hydrophobic ion pair formed between [Co(NCS)4]2− and two protonated molecules of cocaine is responsible for the blue hydrophobic products formed by cocaine in the Scott test.