Hydroxylammonium arsenate

The conditions for preparation of the arsenate are similar to those specified for the phosphate, except that a solution of 312 g. (1 mol) of disodium hydrogen arsenate 7-hydrate in 300 ml. of water (heated to 50° to effect solution) is substituted for the phosphoric acid. Hydroxylammonium arsenate may begin to crystallize before all of the arsenate has been added. An uncooled solution of 40 g. of sodium hydroxide (1 mol) in 100 ml. of water is added to effect neutralization. Three 150-ml. portions of water are used to wash the crude product. The yield is 200 to 210 g. of a product whose purity is approximately 95 per cent based on the hydroxylamine content. Purification can be effected by recrystallization of the arsenate from eight times its weight of water. Recovery amounts to about 145 g. (approximately 60 per cent) of a product with a purity of 98 per cent or better. 

The method for preparation of the oxalate is similar in principle to that used for the corresponding phosphate, the 

Analysis for the hydroxylamine content is effected by the Raschig method. The recommended procedure is a modification of the method given by Scott. Approximately 0.1 g. of sample is dissolved in 75 ml. of water in an Erlen-meyer flask and 30 ml. of a saturated solution of iron(III) ammonium sulfate is added, followed by 10 ml. of 50 per cent sulfuric acid. The solution is boiled for 10 minutes, treated with approximately 5 to 10 ml. of phosphoric acid to reduce the color, then diluted with 200 ml. of water and titrated immediately with standard permanganate solution. 

The normal hydroxylammonium salts of phosphoric, arsenic, and oxalic acids are colorless crystalline com-poimds. They are insoluble in organic solvents, and only sparingly soluble in water at room temperature. Some solubility values from the literature are given below. The solubility of the arsenate and the decomposition points of the three salts were determined on the recrystallized mate- 

Hydroxylammoniuna phosphate serves as a convenient reagent for the preparation of oximes the saturated aqueous solution has a pH of about 5, the pH of maximum rate of oxime formation. 

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NH30H]2C204 Hydroxylammonium oxalate, 3 83 [NIIjOHJsAsOa Hydroxylammonium arsenate, 3 83 [NH30H]3P04 Hydroxylammonium phosphate, 3 82 NH4N3 Ammonium azide, 2 136, 137... 

NH30H]2C204 Hydroxylammonium oxalate, 3 83 [NH30H]8As04 Hydroxylammonium arsenate, 3 83... 

Merry and Zarcinas [33] have described a silver diethyldithiocarbamate method for the determination of arsenic and antimony in soil. The method involves the addition of sodium tetrahydroborate to an acid-digested sample which has been treated with hydroxylammonium chloride to prevent the formation of insoluble antimony compounds. The generated arsine and stib-ine react with a solution of silver diethyldithiocarbamate in pyridine in a gas washtube. Absorbance is measured twice at wavelengths of 600 and 504 nm. 

Hydroxylammonium salts are reagents usually employed as sources of hydroxylamine for various inorganic and organic reactions. The chloride and sulfate are the better known commercially available salts obtained by the hydrolysis of the nitroparaffins. The phosphate, " arsenate, ... 

Arsenic, selenium, and antimony can be measured at low concentrations with HG-AAS. Digestion with aqua regia in a microwave oven is necessary prior to the determination. Next, hydroxylammonium chloride is added as a neutral solution iodide may be added to accelerate the reaction. For arsenic or antimony a reducing agent such as ascorbic acid has to be added to convert all arsenic or antimony to a single oxidation state. A background correction is required for this purpose apparatus with a deuterium lamp corrector can be used but Zeeman background correction is preferred. 

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