Sodium dimethylglyoximate

E. Sodium Dimethylglyoximate.—To a solution of 75 g. of sodium hydroxide in 300 cc. of water is added, with stirring, 100 g. of dimethylglyoxime (Note 11). Heat is applied to effect solution (Note 12), and the mixture is filtered from any slight residue. The solution is poured while hot into 500 cc. of 95 per cent alcohol. After cooling to 50, with stirring, the crystals which form are filtered, then suspended in 150 cc. of alcohol and again filtered, and finally dried at 25° until the solid has no odor of alcohol (Note 13). The yield is 213—230 g. (81-88 per cent of the theoretical amount) of the octahydrate. 

Too long drying, or drying at too high a temperature, partially dehydrates the salt, with the result that it dissolves much more slowly in water and is therefore less desirable for making-solutions for use in qualitative or quantitative analysis. Sodium dimethylglyoximate is extremely soluble in water. A 3 per cent (0.1 M) aqueous solution is suggested to replace the 1 per cent alcoholic solution now used in analytical work. 

Dimethylglyoxime is only slightly soluble in water (0.40 g L 1) consequently it is employed as a 1 per cent solution in ethanol. The sodium salt of dimethylglyoxime Na2C4H602N2,8H20 is available commercially this is soluble in water and may be employed as 2-3 per cent aqueous solution. 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

Precipitation reactions Dimethylglyoxime Lead nitrate Mercury(II) nitrate Silver nitrate Sodium tetraphenylborate Thorium(IV) nitrate Potassium dichromate DME DME DME Rotating Pt Graphite DME DME Ni2 + SO2", MoOj", F" r Cl", Br , I", CN", thiols K + F Pb2 +, Ba2 +... 

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... 

D. Dimethylglyoxime.—The crude biacetyl monoxime, remaining after distilling to 90° and containing about 5 moles of biacetyl monoxime, is added to the sodium hydroxylamine monosulfonate solution (which has been filtered to remove any sediment) and which is contained in a 15-I. flask. It is heated to 70° and allowed to remain warm (with occasional stirring) for several hours (Note 9). The dimethylglyoxime separates in crystals which can be filtered from the solution as soon as it has become cold (Note 10). The crystals are washed with cold water until free of sulfate. The yield of compound melting at 238-240° is 540-575 g-... 

The solution of dimethylglyoxime in sodium hydroxide should not be boiled, since prolonged heating causes decomposition. 

Samples of metal complexes isolated from the final solutions were subjected to microanalysis (for carbon, hydrogen, oxygen, and sulfur). Metals were determined colorimetrically by the following methods— copper as the complex formed with sodium diethyl dithiocarbamate (6) cobalt as the nitroso-R salt complex (7) nickel as the dimethylglyoxime complex (4). 

Dimethylfurazan has been obtained from dimethylglyoxime by heating with water, a.queous ammonia, or aqueous sodium hydroxide.2 3 The usual acid dehydrating agents fail. 

If the product is coloured, dissolve it in 2 m sodium hydroxide solution on a water bath. Filter the hot almost saturated solution, and to the hot filtrate add a concentrated solution of ammonium chloride in excess of the amount required to precipitate all the dimethylglyoxime, i.e. employ an amount greater than the equivalent of the sodium hydroxide used. Filter at once with suction, and wash with boiling water. Recrystallise the white product from rectified spirit. 

---