ThiocyanatocobaltOKs Acid 15? 



THIOCYANATOCOBALTOUS ACID AND ITS ALKALI 



SALTS. 



F. J. Allen and A. R. Middleton, Purdue University. 



When an aqueous solution of K2Co(SCN)4, to which sufficient KSCN 

 has been added to make the solution 0.8-1.0 normal in thiocyanate, is 

 shaken with sufficient 1:4 ethyl alcohol-ether to form a separate layer, 

 only traces of a blue compound pass into the ether layer. If the solution 

 be now acidified with mineral acid, practically all the blue compound 

 passes into the ether layer. As the blue color has been shown by Rosen- 

 heim and Cohn' to be due to a bivalent complex negative ion, Co(SCN)4 " 

 it appears probable that in the acid solution the free acid, H2Co(SCN)4, 

 may be formed which is readily soluble in ether while its potassium 

 salt is nearly insoluble. Two similar acids, H2Hg(SCN)," and 

 HAu (SCN)4 .2H20,:j have been isolated in solid, crystalline form. Pre- 

 liminary attempts to isolate the acid in solid form, by evaporation of the 

 ether solution in an evacuated desiccator, showed that large amounts of 

 HSCN were evolved as the solution concentrated. A mixture was 

 deposited consisting of long slender needles of deep blue color which 

 showed a strong acid reaction when moistened with water and short 

 needles of a bluish green color. No method of separating the two suf- 

 ficiently for analysis has been found up to this time. In order to obtain 

 some information as to the nature of the ether-soluble blue compound, 

 experiments were made to determine the partition of acid, thiocyanate 

 and cobalt between the aqueous and ether layers at 25° C. 



Preliminary determinations were made of the partition of sulfuric 

 acid and of thiocyanic acid. These are recorded in the following tables. 



TABLE 1. Partition of H^SO., between water and 1:4 alcohol (EtOH)- 



ether (Et^O). 



Normality of acid. 



Expt. No. Aq. layer Et^O Layer 



1 0.8005 0.0037 



2 1.7112 0.0074 



The solubility of H^SOi in aqueous ether is very small and in com- 

 parison with the large solubility of HSCN shown in the next table is 

 negligible at total concentrations not above 1.5 normal. 



>Z. anorg. Chem., 27, 280 (1900). 

 - Rosenheim and Colin, loc. cit. 



"■ Bjerium and Kirschner, Die Rhodanide des Goldes, Mem. acad. roy. sci. letties, 

 Danemark, 8me serie, V, No. 1, p. 20. 



"Proc. 38th Meeting, 1922 (1923)." 



