Use of Cobaltous Sulfate in Qualitative Organic Analysis C. A. MAcKENZIE and K. C. EDSON University of Nevada, Reno, Nevada INTRODUCTION
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the solution of the salt c q 66 made sufficientlybasic, blue cobalt6us hydroxide8 will precipitate. Britton4 bas shown that the precipitation of the hydroxide will start a t a pH of 6.81. Aliphatic amines and certain aromatic amines, like benzylamine, are sufficiently strong as bases to bring aboutsthe precipitation of cobaltous hydroxide. Weaker bases, of the order of aniline, although soluble in hydrochloric acid, will not precipitate the hydroxide. Cobaltous sulfate therefore can be used to distinguish between these two types of organic bases.
N THE study of qualitative organic analysis cons~derableemphasis is usually placed on the relationship of molecular structure to solubility. A number of writers have used solubility as a means of classifying organic compounds. For this purpose water, dilute alkalies, dilute acids, and cold concentrated sulfuric acid are usually recommended as solqents. In the procedure followed in the text by Shriner and Fuson' water-soluble compounds are subdivided according to their solubility in ether; acidic compounds, soluble in sodium hydroxide, according to their solubility in soDIRECTIONS FOR TEST dium bicarbonate; and neutral compounds, soluble in The amounts of materials used are the same as those cold concentrated sulfuric acid, according to their solusuggested for solubility tests in the text by Shriner and bility in phosphoric acid. No subdivision is made of Fuson.' the basic compounds soluble in hydrochloric acid. I t is Place 0.2 ml. (0.1 g. of a solid) of the sample in a test the purpose of this paper to describe a reagent that can tube and add 3 ml. of five per cent cobaltous sulfate. be used to classify further such organic bases. Shake the tube and note the formation or non-formation In order to make the proposed subdivision a precipiof blue cobaltous hydroxide. If a precipitate does not tation reaction, rather than a solubility test, is emimmediately form set the test tube aside; if the precipiployed. The reagent used, cobaltous sulfate, dissolves Interesting discussions on the formation of coh$tous hyin water to give a red colored solution with a pH value may be found in the following references: of approximately 4.6 for a five per cent solution.' If droxide STILLWELL, "The colors of cobaltous hydroxide," J. Phys.
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S M H I AND N ~ PUSON."ldenrificnrion of organic compounds," 2nd ed ,John Wiley and Sons. Inc.. Xew \'o'ork City. 1940, p. 4 . L)I
