Arsenious Compounds

Both the chromium(III) catalyzed and uncatalyzed oxidations of arsenic(III) by cerium(IV) have been studied in varying concentrations of sulfuric acid. The 

The kinetics of the formation of dihydrogen from the reaction of the iron complexes [l.ljferrocenophane, 3,3 -trimethylene[l.l]ferrocenophane, and 2,2 -trimethylene[l.l]ferrocenophane in strong acids have been studied by using tensiometric and spectrometric techniques.The results of these measurements are consistent with the three-step mechanism proposed for the formation of dihydrogen a very fast initial protonation, a slower second protonation, and the elimination of dihydrogen as the rate-determining step. A primary kinetic isotope effect, kn/ D, of between 3 and 5 was observed for [l.ljferrocenophane. The rate 

---

Arsenious Compounds.— (1) H,S, a yellow color in neutral or alkaline liquids a yellow ppt. in acid liquids. Tlie ppt. dissolves in solutions of the alkaline hydrates, carbonates, and sulpbydrates but is scarcely affected by HCl. Hot HNO decomposes it... 

Reinsch test,—The suspected liquid is acidalated with one-sixth its bulk of HGl strips of electrotype copper are immersed in the liquid, which is boiled. In the presence of an arsenious compound a gray or bluish deposit is formed upon the Cu. A similar deposit is produced by other eubatances (Bi,... 

Arsenic Compounds.—>(1.) H,S does not form a ppt. in neutral or alkaline solutions. In acid solutions it first reduces the arsenic to an arsenious compound, which is then decomposed with precipitation of the yellow As,S. 

AgNO xinder the same conditions as with the arsenious compounds, produces a brick-red ppt. of silver arsenate. 

Arsenic compounds behave like arsenious compounds with the tests 4, C and 7 for the latter. 

Another suitable method for the determination of arsenious compounds is by iodate titration this is particularly useful for the determination of arsenic isolated by hydrochloric acid distillation, the amount of mineral acid being adjusted to be equivalent to about 50 per cent of strong acid before titration. The method is described in detail under Halogen Acids, p. 292. 1 ml 0 05M iodate -= 0 009895 g AS2O3. 

It is usually preferable to oxidise the compound directly as follows. Intimately mix 0 02-0 05 g. of the eompound with 3 g. of sodium peroxide and 2 g. of anhydrous sodium carbonate in a niekel erucible. Heat the crueible and its eontents with a small flame, gently at first, afterwards more strongly until the eontents are fused, and eontinue heating for a further 10 minutes. Allow to stand, extract the contents of the crucible with water, and filter. Add exeess of eoneentrated nitrie acid to the filtrate and test with ammonium molybdate reagent as above. A yellow preeipitate indicates the presenee of phosphorus. It must be borne in mind that the above treatment 1 eonvert any arsenie present into arsenate. 

Arsenious oxide, trivalent antimony (73), sulfurous acid (74), hydrogen sulfide (75), stannous ion, and thiocianate (76) have been recommended for the titration of iodine. However, none of these appears to have a greater sensitivity for the deterrnination of minute quantities of iodine than thiosulfate. Organic compounds such as formaldehyde (77), chloral hydrate (78), aldoses (79), acetone (70,80), and hydroquinone have also been suggested for this purpose. 

Arsenic Peroxides. Arsenic peroxides have not been isolated however, elemental arsenic, and a great variety of arsenic compounds, have been found to be effective catalysts ia the epoxidation of olefins by aqueous hydrogen peroxide. Transient peroxoarsenic compounds are beheved to be iavolved ia these systems. Compounds that act as effective epoxidation catalysts iaclude arsenic trioxide, arsenic pentoxide, arsenious acid, arsenic acid, arsenic trichloride, arsenic oxychloride, triphenyl arsiae, phenylarsonic acid, and the arsenates of sodium, ammonium, and bismuth (56). To avoid having to dispose of the toxic residues of these reactions, the arsenic can be immobi1i2ed on a polystyrene resia (57). 

The toxicity of arsenic ranges from very low to extremely high depending on the chemical state. Metallic arsenic and arsenious sulfide [1303-33-9] AS2S2, have low toxicity. Arsine is extremely toxic. The toxicity of other organic and inorganic arsenic compounds varies (28). 

The solubility of AS2O3 in water, and the species present in solution, depend markedly on pH. In pure water at 25°C the solubility is 2.16 g per lOOg this diminishes in dilute HCl to a minimum of 1.56g per lOOg at about 3 m HCl and then increases, presumably due to the formation of chloro-complexes. In neutral or acid solutions the main species is probably pyramidal As(OH)3, arsenious acid , though this compound has never been isolated either from solution or otherwise (cf. carbonic acid, p. 310). The solubility is much greater in basic solutions and spectroscopic evidence points to... 

The fact that practically all aromatic amines are readily converted into diazo compounds contributed greatly to Griess s success. The original method (Griess, 1858) by which he diazotized picramic acid (1.1 see Scheme 1-1) consisted of passing nitrous gases, prepared by the reduction of nitric acid with starch or arsenious acid, into an alcoholic solution of the amine. 

Organochlorine or -bromine compounds are burned in the presence of aqueous solutions of arsenious oxide (AS2O3) or hydrazine hydrochloride (N2H4.2HCI). These solutions are effective in reducing the elemental chlorine or bromine formed to the chloride or bromide ions according to the reactions (X = Cl, Br) [61,62,64-66] ... 

With Arsenic —Hydrogen does not directly combine with arsenic, but if an arsenic compound is in solution in a liquid in which hydrogen is being generated, i.e. hydrogen in the nascent state, chemical union takes place. Thus, if arsenious oxide is dissolved in dilute hydrochloric acid and a piece of metallic zinc is added, the hydrogen produced by the action of the add on the zinc will combine with the arsenic, in accordance with the following equation —... 

On his way home from the Netherlands he studied mining and metallurgy in the Harz, and in 1727 he was placed in charged of the chemical laboratory at the Bureau of Mines in Stockholm, which was then in poor financial condition. After the laboratory was sold, Brandt and his students Henrik Teofil Scheffer and Axel Fredrik Cronstedt carried on their epoch-making researches at the Royal Mint, and in 1730 Brandt became assay master of the Mint. Three years later he published a systematic investigation of arsenic and its compounds in which he showed that arsenic is a semi-metal and that white arsenic [arsenious oxide] is its calx (35). 

By the action of nascent hydrogen upon soluble arsenic compounds, as by the introduction of arsenious acid into on apparatus evolving hydrogen —... 

A monobasic arsenious acid, OHo, conosponding to ni-trous aoid, appears to exist, one of its compounds, AsOAmo, being known. Arsenious aoid when boiled with cupric aco. tato yields SchweinfUrt green, 8A ,0,Cuo", Ou(CjH,OJ,. 

By the distillation of potassio acetate with arsenious anhydride, a compound known as cacodyl, As",Me, is produced. This substance may also be prepared by the action of methylie iodide upon an alloy of soffium and arsenic containing A8, Na. -... 

By this process there is less teudenoy to form compounds containing both positive radicab and negative elements. Potas sium or sodium compounds are never produced in this reaction, because they cannot exist in the presence of ethylio iodide or its homologues. This process is well adapted for the formation of arsenie, antimony, tin, mercury, lead, bismuth, and tellurium compounds —... 

The substance described as tetrammino-arsenie iodide, [As(NH3),]I3, is a yellow powder which loses ammonia on heating above 50° C., and at 300° C. decomposes into arsenic, nitrogen, and ammonium iodide. If the compound be cooled to 0° C. and ammonia again passed over it, a pale yellow liquid, of composition [As(NIT3)12]I3, is formed. Ilugot again obtained only the amide, As(NH2)3, on treating1 the iodide with ammonia gas. 

Arsenious oxide is insoluble in dilute sulphuric acid but reacts with fuming sulphuric acid to give a series of very unstable crystalline compounds of general formula As203.nS03. These are resolved into arsenious oxide and sulphuric acid on contact with water. The formation of a crystalline arsenyl tartrate, Na(As0)C4H406, analogous to potassium antimonyl tartrate, has been cited as evidence of the basic nature of arsenious oxide, but the product may contain the arsenic in a complex anion. 

---