Nickel dimethylglyoxime

The base was being prepared by distilling a mixture of hydroxylamine hydrochloride and sodium hydroxide in methanol under reduced pressure, and a violent explosion occurred towards the end of distillation [1], probably owing to an increase in pressure above 53 mbar. It explodes when heated under atmospheric pressure [2], Traces of hydroxylamine remaining after reaction with acetonitrile to form acetamide oxime caused an explosion during evaporation of solvent. Traces can be removed by treatment with diacetyl monoxime and ammoniacal nickel sulfate, forming nickel dimethylglyoxime [3], An account of an extremely violent explosion towards the end of vacuum distillation had been published previously [4], Anhydrous hydroxylamine is usually stored at 10°C to prevent internal oxidation-reduction reactions which occur at ambient temperature [5], See other REDOX REACTIONS... 

The formation of nickel dimethylglyoximate complex may be expressed as follows ... 

Figure 4.29. (a) The crystal structure of nickel dimethylglyoximate projected along the c0 axis, (b) The dimensions of the molecule are shown with atom numbering shown in (a). 

Dimethylglyoxime reagent soluble red iron(II) dimethylglyoxime in ammoniacal solution. Iron(III) salts give no colouration, but nickel, cobalt, and large quantities of copper salts interfere and must be absent. The test may be carried out in the presence of potassium cyanide solution in which nickel dimethylglyoxime (cf. Section III.27, reaction 8) dissolves. 

A useful spot test utilizes the fact that a suspension of red nickel dimethylglyoxime in water when treated with a neutral or acetic acid solution of a palladium salt yields the yellow palladium dimethylglyoxime, which is sparingly soluble in dilute acids. The test is best performed with dimethylglyoxime paper the latter is prepared as follows. Immerse drop-reaction paper in a 1 per cent alcoholic solution of dimethylglyoxime, dry, then immerse again in a solution of 05m nickel chloride rendered barely ammoniacal. The nickel complex precipitates wash thoroughly with water, immerse in alcohol and dry. 

Place a drop of the neutral or acetic acid test solution upon nickel dimethylglyoxime paper, and almost dry by waving over a flame. Immerse the paper in dilute hydrochloric acid until the surface surrounding the fleck becomes white, and then wash the paper with cold water. A pink to red spot remains, depending upon the quantity of palladium present. The acid-stable palladium dimethylglyoxime at the site of the fleck protects the underlying red nickel dimethylglyoxime from attack by the acid. 

Wash the precipitate in thi example,"the nickel dimethylglyoximate can be washed with.cold water until qualitative testing shows.that the wash sgju-. tion is free of chloride ions. a... 

Analytical Methods. Carbon, hydrogen, nitrogen, and sulfur analyses and Hempel distillations (IS) were performed using conventional analytical techniques. Nickel and vanadium contents were determined by the methods of Bean (14). These methods involve the colorimetric determination of nickel dimethylglyoxime and tungstovanadic acid, respectively. Simulated distillations were done by the method of Poulson... 

Figure 8-2 shows a selection of electron photomicrographs of barium sulfate and nickel dimethylglyoxime precipitates formed under a variety of conditions. The size and shape of precipitate particles clearly varies widely with the nature of the precipitate and the mode of precipitation. The perfection of crystals of the same size also varies with conditions. Particle size as reflected by a linear dimension may be misleading. 

Some nickel compounds have important uses also. Many of these compounds are used in electroplating. Some are used to make alloys of nickel. Other nickel compounds are used as coloring agents. For example, the compound nickel dimethylglyoxime (CgHi4N4Ni04) is used as a coloring agent in paints, cosmetics, and certain kinds of plastics. 

A simple procedure for the preparation of Ni/Si02 catalysts involves the precipitation of nickel dimethylglyoxime from a suspension of silica in an aqueous solution of a nickel salt.38,39 Calcination is not required since the resulting supported precipitate is easily reduced in a stream of hydrogen at 200°-250°C, giving very highly dispersed supported nickel catalysts. 

Nickel dimethylglyoxime is spectacular in appearance. As shown in color plate 7, it has a beautiful vivid red color. 

Nickel dimethylglyoxime is a bulky precipitate that is inconvenient to manipulate in amounts greater than 175 mg. The amount of nickel in a type of permanent-magnet alloy ranges between 24% and 35%. Calculate the sample size that should not be exceeded when analyzing these alloys for nickel. 

Choose an appropriate precipitant and carry out the precipitation reaction. Here, an alcoholic solution of dimethylglyoxime could be used to precipitate nickel from a hot solution of aqua regia, by adding a slight excess of aqueous ammonia solution, forming a red precipitate of nickel dimethylglyoximate (Fig. 20.3). 

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