Tris 3-cyanomethyl-2,4-pentanedionato chromium III

Tris(3-cyanomethyl-2,4-pentanedionato)chromium(III), [Cr H8CC(0)C(CH2CN)C(0)CH, 3] has recently been prepared by the aminomethylation of tris(2,4-pentanedionato)-chromium(III) followed by quaternization of the amine and subsequent displacement of trimethylamine with alkali metal cyanide.1 The procedure described below is a modification of 

To a mixture of 11.0 g. (0.031 mole) of tris(2,4-pentanedio-nato) chromium (III)2 and 4.0 g. (0.12 mole) of powdered paraformaldehyde in 150 ml. of glacial acetic acid is added 12.5 ml. (0.12 mole) of iV iVW -tetramethyldiaminomethane, prepared according to Lindsay and Hauser.3 After stirring for 12 hours at room temperature, the acid is neutralized by slow addition to 700 ml. of saturated aqueous potassium carbonate. Sufficient quantities of ice are added periodically to keep the neutralization solution below room temperature. An excess of ammonium hydroxide is then added to make the solution basic. The triamine is extracted into chloroform from which it is recovered as a red-purple tar by evaporation (end of step a). 

The crude triamine is dissolved in 200 ml. of 50% ethanol-water solution (v/v), and 30 ml. (68.4 g., 0.48 mole) of methyl iodide is added. After stirring half an hour, 20 ml. of ethanol is added. Stirring is continued for an additional 2 hours, after which the mixture is diluted with 50 ml. of water (end of step 6). A solution containing 14 g. (0.21 mole) of potassium cyanide dissolved in 75 ml. of water is then added. After stirring for 2 hours, the solution is extracted with chloroform to give a dark organic solution which is evaporated to a purple tar. Chromatography on Merck alumina, f with 2 1 benzene-chloroform as the eluent, effects the separation of pure tris(3-cyanomethyl-2,4-pen-tanedionato)chromium(III) (end of step c). The pure chelate 

The triamine is extremely hygroscopic and soluble in both water and n-heptane. Because of this amazing solubility range, it cannot be crystallized easily. The crude triamine can be partially purified by chromatography on a column of alumina, with 50 50 (v/v) benzene-chloroform as the eluent, but is extremely difficult to isolate in a pure state. 

The trisquaternary salt (product of equation 6) is a pale purple powder which can be isolated by addition of dioxane to the ethanol-water mixture followed by filtration. In cases where the isolation of the salt is desired, better yields can be obtained by carrying out the quaternization reaction in dioxane solution. Isolation is then accomplished by addition of ethyl ether and filtration. Preliminary experiments in which laboratory animals were injected with solutions of the crude salt indicated a high degree of toxicity. 

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