Arsenic pentachloride

In addition to the trihalides, arsenic and antimony form penta-fluorides and antimony a pentachloride it is rather odd that arsenic pentachloride has not yet been prepared. 

Arsenic pentachloride [22441-45-8] (arsenic(V) chloride), AsQ., is produced by irradiation of a solution of AsQ. chlorine at —105°C using ultraviolet light (22). Arsenic pentachloride is a pale yellow soHd (presumably because of an entrained chlorine impurity) which melts with partial decomposition at —50° C. Raman spectra show that it is a trigonal—bipyramidal molecule both in solution and in the soHd state. 

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 pentachloride, instability of, 7 7-8 Arsenic pentafluoride, 7 2, 4, 5 chalcogen(IV) compound adducts, 35 259-261... 

There is a definite tendency for the nonmetals of the fourth row—As. Se, and Br—to be unstable in their maximum oxidation state. For example, the synthesis of arsenic pentachloride eluded chemists until comparatively recently, v although both PCI, and SbCI, are stable. The only stable arsenic pentahalide is AsFs AsCU decomposes at -50 °C, and AsBrs and Asl5 are still unknown. 

One compound only of these two elements has been isolated, namely, arsenic trichloride, which at ordinary temperatures is a colourless oily liquid. Although a substance reported to be arsenic pentachloride has been described in the literature (see p. 110), evidence of the existence of such a compound is not forthcoming. 

Arsenic Pentachloride ( ), AsC15.—By the action of chlorine on arsenic trichloride at a low temperature Baskerville and Bennett 1 obtained a greenish-yellow liquid which they believed to be arsenic pentachloride. Pure solid arsenic trichloride was placed in a vessel surrounded by carbon dioxide snow and saturated with chlorine, the temperature being -88° C. The liquid approximated in composition to AsCIj. It was soluble in carbon disulphide and in ether, and the ether solution, on evaporation at -80° C., left yellow crystals which readily decomposed with slight rise in temperature. The formation of this compound has not been confirmed, however, and its existence is doubtful. 

Typical oxidising dopants used include iodine, arsenic pentachloride, iron(III) chloride and NOPF6. A typical reductive dopant is sodium naphthalide. The main criteria is its ability to oxidise or reduce the polymer without lowering its stability or whether or not they are capable of initiating side reactions that inhibit the polymers ability to conduct electricity. An example of the latter is the doping of a conjugated polymer with bromine. Bromine it too powerful an oxidant and adds across the double bonds to form sp3 carbons. The same reaction may occur with NOPF, but at a lower rate. 

Arsenic pentachloride can be prepared at low temperature but decomposes above —50°C. Antimony pentachloride is made by reaction of Cl2 with SbCl3 and is stable up to 140°C. The solid (mp 4°C) contains Cl4Sb(/x-Cl)2SbCl4 dimers. The curious instability of AsC15 relative to PC15 and SbCl5 has been attributed to a stabilization of the 4s2 electron pair in all the elements immediately following the... 

Arsenic pentachloride was an elusive compound until it was finally obtained by the ultraviolet irradiation of an ASCI3/CI2 mixture at -105 °C. Above —50°C, a redox reaction occurs affording AsCb and molecular chlorine (see equation 14 above). The identity of AsCls was confirmed by elemental analysis and by comparison of its Raman spectrum with those of liquid PCI5 and SbCls. ... 

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