Hydrogen arsenate, preparation

Ferrous Hydrogen Orthoarsenates have not been prepared in the pure state. According to Wittstein,8 the dihydrogen arsenate remains in the mother liquor when the normal orthoarsenate is precipitated (see equation above) and when iron is acted upon by arsenic acid over a long period an asbestos-like deposit is formed which probably contains a ferrous hydrogen arsenate.9... 

Prepare a solution of 25 g ammonium molybdate in 450 ml distilled water. Add, with stirring, 21 ml concentrated sulfuric acid and 25 ml of distilled water containing 3 g disodium hydrogen arsenate heptahydrate. Continue stirring 24 hr at 37°C, then store the solution in a 1 liter glass-stoppered brown bottle up to 6 months at room temperature. 

Potassium arsenates.—Potassium arsenate, K3As04 dipotassium hydrogen arsenate, K2HAs04and potassium dihydrogen arsenate, KH2As04, have been prepared. Their heats of formation are respectively 396-2 Cal., 339-8 Cal., and 234-0 Cal.5 The last mentioned has a density of 2-851 at ordinary temperatures,6 and of 2-8675 at 9-2° C.7 Potassium meta-arsenate, KAs03, has a specific heat of 0-1568 between 17° and 99° C.8... 

It may be prepared by the action of disodium hydrogen arsenate upon ferrous sulphate solution —6... 

Caldum and lithium carbonates in small quantities exert a favorable action. Carbonic add, iron, and metallic aluminium act as exdtants of the secretion, the effect of iron and aluminium being related to that of hydrogen. As other substances favoring the secretion, we may mention certain arsenical preparations, as well as medicinal preparations containing iodine. 

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. 

Arsenic forms a volatile trifluoride, ASF3, and a fairly volatile trichloride, ASCI3, which fumes in air. The latter is prepared by passing dry hydrogen chloride over arsenic(lll) oxide at 500 K ... 

Arsenic pentasulfide (arsenic(V) sulfide), As S q, is stable in air up to 95°C, but at higher temperatures begins to dissociate into arsenous sulfide and sulfur. It is prepared by the fusion of arsenic with sulfur foUowed by extraction with ammonia and reprecipitation at low temperatures by addition of hydrochloric acid. Arsenic pentasulfide is precipitated at low temperatures from strongly acidic arsenate solutions by a rapid stream of hydrogen sulfide. It is hydrolyzed by boiling with water, yielding arsenous acid and sulfur. Salts derived from a number of thioarsenic acids are formed from arsenic pentasulfide and alkaH metal sulfides. 

Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

Arsenic pentasulfide is prepared by precipitation from an acidic solution of orthoarsenic acid, H3ASO4, or arsenic pentachloride, AsCls or any other soluble As(V) salt by passing hydrogen sulfide. It may be also prepared by heating a mixture of arsenic and sulfur, extracting the fused mass with ammonia solution and reprecipitating arsenic pentasulfide at low temperature hy addition of HCl. 

Arsenic sesquioxide may be prepared by heating arsenic trioxide with hydrogen sulfide ... 

Gallium arsenide is prepared by passing a mixture of arsenic vapor and hydrogen over gallium(lll) oxide heated at 600°C ... 

Three- and five-membered rings (AS2S and AS2S3) have also been structurally characterised for the arsenic-sulfur system. The diarsathiiran cyclo-(RAs)2S [R = C(SiMe3)3] is prepared by the addition of sulfur to the diarsene RAs=AsR. The non-planar five-membered ring cyclo-(PhAs)2S3 is obtained, in addition to cyclo-(PhAsS)4, from treatment of phenylarsenic acid with aqueous ammonia and hydrogen sulfide. ... 

Arsenic(III) fluoride is prepared by reacting arsenic(III) oxide with hydrogen fluoride, with calcium fluoride and sulfuric acid, or with fluorosulfonic acid.12... 

Impubities.—rhosphorus is rarely adulterated, and the only impurities contained in it are those derived from the acid used in its preparation. Dumas considers flexibility as a characteristic of good phosphorus. Occasionally arsenic, antimony, bismuth, and some other metals have boon found in it. If the acid used contained arsenioua acid, or an oxide of antimony, these are reduced in the process of manufacture of phosphorus, and are found in it in the metallic state. A solution of phosphorus in dilute nitrio acid should give no precipitate with sulphide of hydrogen, and the precipitate procured by a barytic salt should be entirely soluble in excess of nitric acid, proving the absence of sulphur. If arsenic is present, the solution in nitrio acid deposits a black precipitate of metallic arsenic when submitted to evaporation. 

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