Potassium cobalt nitrite cobaltinitrite

Cobalt Nitrite Complexes. When KNOz is added in excess to a soln of Co(NOa)2,acidified with AcOH, a yel ppt of potassium hexa-nitrocobaltiate (potassium cobaltinitrite),... 

Evaporation by heating a filtrate from precipitation of potassium cobaltinitrite caused it to turn purple and explode violently [1]. This was attributed to interaction of nitrite, nitrate, acetic acid and residual cobalt with formation of fulminic or methylnitrolic acids or their cobalt salts, all of which are explosive [2], Mixtures containing nitrates, nitrites and organic materials are potentially dangerous, especially in presence of acidic materials and heavy metals. A later publication confirms the suggestion of formation of nitro- or nitrito-cobaltate(III) [3],... 

Cobaltic Potassium Nitrite, Hexakis(nitrito-N)co-baltateiJ—) tripotassium potassium hexanitrocobaltateOll) potassium cobaltinitrite potassium nitrocobaltate(lll) cobalt yellow Fischer s yellow C.l. Pigment Yellow 40 C.I. 77357. CoKjNjOmol wt 452.29. Co 13.03%, K 25.93%, N 18.58%, 0 42.45%. K3Co(N02)6. incorrectly called Indian yellow". Prepd by addition of KNO, to a solution of a Co salt Salyer, Sweet, Anal. Chem. 32, 548 (1962). 

According to Comman, the principal preparation method was by the acidification of solutions of cobalt salts with acetic acid followed by addition of a concentrated potassium nitrite solution. Cobalt yellow would then slowly precipitate as a yellow crystalline mass. The alternative Hayes method involves nitric acid vapours being passed into a solution of cobalt nitrate and potassium hydroxide (or acetate). Finally, a method where solutions of sodium cobaltinitrite and a potassium salt acidified with acetic acid is used was reputedly devised by DeKoninck and published by Adie and Wood (1900 cf. Cornman) as an analytical test but subsequently used to produce pigmentary grades. 

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