ARSENIC TRI IODIDE

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... 

Tetramethylarsonium iodide, (CH3)4AsI.— The double compound of the iodide with arsenic tri-iodide is formed when powdered arsenic and methyl iodide are heated together at 160° to 200° C. If this reaction is carried out at ordinary temperatures or on the w ater-bath, the principal products are methyldi-iodoarsine and tetramethylarsonium iodide arsenic tri-iodide and a small quantity of cacodyl iodide arc also produced. When methyl iodide is ded to sodium arsenide in an atmosphere of carbon dioxide, the mixture on distillation gives cacodyl and tetramethylarsonium iodide, Cacodyl and methyl iodide react with evolution of heat, yielding the arsonium compound and cacodyl iodide according to the equation ... 

Ethyldi-iodoarsine, CaHjAsIa, is prepared by distilling diethyl-iodoarsine with iodine, or by heating ethyl iodide and arsenic at 100° C. for several days, arsenic tri-iodide and tetraethylarsonium iodide being formed at the same time. It may also be isolated by the interaction of ethyldichloroarsine ajtid sodium iodide in dry acetone solution. It is a reddish-yellow oil, B.pt. 126° C. at 11 mm., crystallising at —9° C., and is oxidised by silver oxide to ethylarsinic acid. ... 

The most important range for inorganio chemicals is between 1 40 and 1 70. But there are some substances, such as certain oxides and sulphides, whose indices lie well above this range, or even well above 2 0. Media which are liquid at room temperature and have such high refractive indices are not available, but certain mixtures of substances which solidify to glasses may be used. A little of the medium is melted on a microscope slide, the substance under examination is dusted into the melt, a cover-glass is pressed on, and the slide is then allowed to cool. Substances which have been used in this way are mixtures of piperine with arsenic and antimony tri-iodides (for indices 1 7-2 1), mixtures of sulphur and selenium (2-0-2-7)—for details, see Larsen and Berman (1934)—and mixtures of the halides of thallium (Barth, 1929). 

Dinitro-p-diphenyl carbizide Arsenic (III), As+3 Silver nitrate Copper (II) sulfate Potassium tri-iodide (Kl + l2)... 

Phenyltrimethylarsonium tri - iodide, CgHg. As(CHg)3l3, is formed amongst other products by the interaction of methyl iodide and any of the following arsenicals Phenylmethylchloro- or iodoarsine, arsenobenzene or 52/J .-diphenyldi-iododiarsine. It forms reddish-brown needles, M.pt. 108° C., which arc converted by arsenobenzene or sym.-diphenyldi-iododiarsine into phenyltrimethylarsonium iodide and phenyldi-iodoarsine. 

Heating with hydriodic acid or phosphorus tri-iodide in sealed tubes, decomposes arseno-compounds to hydrocarbons, arsenious iodide, and elemental arsenic. Sulphur gives arylarsenious sulphides, but an excess of the element at higher temperatures may cause decomposition ... 

Tris(dimethyIamino)arsine is prepared by dimethylaminolysis of arsenic(III) chloride in a suitable solvent. The reaction is generally applicable since arsenic(III) iodide and alkyl-haloarsines of the general formula R AsX3 (ra = 1 or 2, X = Cl, Br, or I) have been reported to react similarly with secondary amines. In addition to dimethylamine, other secondary amines, such as diethylamine, have been used to prepare the corresponding tris(dialkylamino)arsine. Tris(dialkyl-amino) arsines have also been prepared by transamination of tris(dimethylamino) arsine with higher-boiling secondary amines such as diethylamine, di-n-butylamine, or piperidine. 

Potassium iodide solution in the presence of concentrated hydrochloric acid, iodine is precipitated upon shaking the mixture with 1 -2 ml of chloroform, the latter is coloured violet by the iodine. The reaction may be used for the detection of arsenate in the presence of arsenite oxidizing agents must be absent. Excess of the reagent dissolves iodine to form tri-iodide ions. 

With the exception of antimony (V), which requires the presence of iodide for its reduction, all species can be reduced in an acid medium at a pH of 1 -2. However, the reduction of some species, including antimony (III), arsenic (III), and all tin species, will also proceed at higher pH, where arsenic (V) and antimony (V) are not converted to their hydrides. This effect permits the selective determination of the various oxidation states of these elements [714, 716]. In the case of tin, reduction can be achieved at the pH of the Tris-HCl... 

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... 

The masking of coordinated arsine toward the quaternization reaction with methyl iodide has been used to demonstrate the coordination of all of the arsenic atoms of the ligand tris(orthodiphenylarsinophenyl)arsine (QAS) in its complex with platinum (II) 9, 53). This reaction is found with uncoordinated arsines. 

The method is applicable for triorganoarsenic compounds bearing aryl or vinyl substituents (equations 76 , 77 and 78 ), while for the preparation of alkylarsenic halides this method has not been useful since only adduct formation and redox reactions have been reported between R3AS and AsXj (equations 79a and b) . Reaction of tris(trifluoromethyl) arsine with arsenic iodide, however, has been reported to afford a mixture of halides (equation 80) . In the reaction of unsymmetrically substituted compounds such as 4, cleavage of the aryl-arsenic bond is preferred to that of the alkyl-arsenic bond (equation 78 ). The cleavage of 4 by this method is in contrast to that of 3 in thermolysis (equation 75). 

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