Arsenous triiodide

Arsenic triiodide [7784-45-4] M 455.6, m 146°, b 400°/atm. Crystd from acetone, sublimes below 100°. POISONOUS... 

Arsen-jodid, n. arsenic iodide, specif, arsenic triiodide. arsenic(III) iotUde. -jodiir, n. 

Reaction with potassium bromide or iodide forms arsenic trihromide or arsenic triiodide. 

Formula Asia MW 455.635 pyramidal molecule with covalent bonding Synonym arsenic (III) iodide triiodoarsine arsenous triiodide... 

Arsenic triiodide is prepared by treating elemental arsenic with a solution of iodine in carbon disulfide. Alternatively, it can be precipitated out from a hot solution of arsenic trioxide or arsenic trisulfide in hydrochloric acid on treatment with potassium or sodium iodide. Also, it is made by the reaction of arsenic trichloride with potassium iodide. 

Arsenic triiodide, preparation of, 7 15 Arsenic(V), C-containing compounds, 28 204-216... 

Triphenylarsine has been prepared by the action of arsenic triiodide or arsenic trichloride on phenylinagnesium Ijromide... 

Ammino-arsenic Tri-iodides.—Several compounds of arsenic tri-iodide have been prepared. Bamberger and Philipp 4 obtained a compound, [As4(NII3)9JI, by passing dry ammonia gas into arsenic triiodide in ether, when a bulky white precipitate was produced. On heating to 50° C. it loses ammonia, and is completely decomposed at higher temperatures. Arsenic tri-iodide absorbs ammonia, slowly at first, and then more rapidly towards the point of saturation. The compound produced is a tetrammino-derivative.1... 

Crystalline arsenic triiodide consists of discrete Asl3 molecules, which are stacked such that the iodine atoms are hexagonally close packed. The arsenic atoms are octahedrally surrounded by iodine, but with the arsenic off-centre resulting in two sets of d(As—I) (Table 9) three bonds of 2.59 A and three of 3,47 A (cf. Asl3 vapour, d(As—I) 2.56 A). Arsenic(III) triastatine has not yet (mid-1986) been reported, although it would be surprising if the synthesis has not been attempted. 

Concentrated hydrochloric acid also dissolves the trichloride, about 100 g. of the latter dissolving in 1 litre of acid at 100° C.7 Dissolution in hydriodic acid is accompanied by evolution of heat and the triiodide is formed.8 Ethyl iodide reacts similarly.9 Double decomposition reactions occur w hen arsenic trichloride is heated with phosphorus triiodide, stannic iodide or germanium iodide, the reactions being complete.10 Similarly, potassium iodide heated with arsenic trichloride in a sealed tube at 210° C., and potassium bromide at 180° to 200° C., form respectively arsenic triiodide and tribromide.11 Stannous chloride, added to the solution in hydrochloric acid, causes reduction to arsenic (see p. 29). Arsenic trichloride may be completely separated from germanium chloride by extraction with concentrated hydrochloric acid.12 Ammonium, sodium and cobaltic chlorides react with arsenic trichloride to form additive compounds with magnesium, zinc and chromic chlorides there is no reaction.13... 

Arsenic triiodide also dissolves, the saturated solution at 15° C. having density 3-661. Other soluble halides are potassium bromide, anhydrous ferric and aluminium chlorides 6 and tetramethyl ammonium iodide but the iodides of rubidium, cadmium, manganese and cobalt, also mercuric and stannic iodides, and cobalt and stannic bromides, are insoluble or only very slightly soluble in arsenic tribromide. The liquid also dissolves phosphoryl bromide and, very slightly, ammonium thiocyanate. In the mixed solutions of halides, the components may react chemically (cf. p. 106), but such is not always the case for example, with antimony tribromide a continuous series of solid solutions is formed.7... 

Many other methods of preparation have been employed. For example, the triiodide is formed when arsenious oxide,5 or a mixture of this oxide with sulphur,6 is heated in iodine vapour or when arsenious oxide is heated with iodine,7 hydriodic acid,8 a mixture of potassium iodide and acetic acid,9 or a mixture of potassium iodide and potassium hydrogen sulphate.10 When arsenic disulphide and iodine, in the proportions 1 As Ss 3la, are heated together, arsenic triiodide is formed.11 When arsenic trisulphide is fused with an excess of iodine, the product is soluble in carbon disulphide and the solution on evaporation deposits arsenic triiodide, then a sulphiodide and finally sulphur with excess of sulphide the product is the sulphiodide, AsS2I. If a solution of iodine in carbon disulphide is added to arsenic di- or tri-sulphide, the triiodide and sulphur are formed. The triiodide is also produced when a mixture of the trisulphide and mercuric iodide is heated 12. when hydriodic... 

Arsenic triiodide is soluble in carbon disulphide, alcohol, ether, chloroform, benzene, toluene and the xylenes.5 The solution in carbon disulphide gradually darkens owing to absorption of oxygen and liberation of iodine.6 With alcohol at 150° C. ethyl iodide is formed. In methylene iodide 5 the triiodide dissolves to the extent of 17-4 parts of AsI3 in 100 parts of solvent at 12° C. The dipole moment in various solvents has been determined.7... 

In the solid and liquid forms, arsenic triiodide is a non-conductor of electricity, but some of its solutions are weak conductors 10 thus, a saturated solution in allyl isothiocyanate at 60° C. has a conductivity of 1-4 x 10-4 mho. 

Chemical Properties.—When heated above 100° C. arsenic triiodide dissociates slowly into its elements above its melting point this decomposition becomes more rapid.11 In air, the products are arsenic, arsenious oxide and iodine, and the action proceeds slowly even below 100° C. and is rapid at 200° C. at higher temperatures the triiodide burns with a pale blue flame.12 Heated in an atmosphere of nitrogen in... 

Dry hydrogen sulphide in the cold does not react with arsenic triiodide. At 200° C. some of the latter volatilises and is carried away by the gas stream, while the remainder is converted 6 to a crystalline iodosulphide, A 2S5I. The aqueous solution with hydrogen sulphide yields a precipitate of arsenic trisulphide.7... 

Arsenic Pentiodide ( ), Asls.—When a mixture of arsenic and iodine in the requisite proportions is heated in an atmosphere of carbon dioxide in a sealed tube at 150° C., a brown crystalline product is obtained.3 The crystals, which melt at 70° C. and have density 3-93, are soluble in water, carbon disulphide, alcohol, ether and chloroform. The solution in carbon disulphide yields, when allowed to crystallise, a mixture of arsenic triiodide and iodine. The latter is readily lost from the pentiodide, and heating at 100° C. in nitrogen in a sealed tube brings about the decomposition. Like the triiodide, the pentiodide dissolves boron tribromide.4... 

Volumetric Methods.—Iodometrically. A hot solution of arsenious oxide or an arsenite in concentrated hydrochloric or sulphuric acid when treated with potassium iodide gives a red precipitate of arsenic triiodide. 

Arsenic triiodide has been prepared by direct union of the elements with or without a solvent,1 by the reaction of iodine with arsenic trioxide2 or sulfide,3 and by the reaction of aqueous solutions of an arsenic compound and an iodide.4 The last mentioned furnishes the most convenient method of obtaining the material in pure form. 

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