Arsenic halides

Arsenic Halides. Arsenic forms a complete series of trihaUdes, but arsenic pentafluoride is the only well-known simple pentahaUde. AH of the arsenic haUdes, the physical properties of which are given in Table 2, are covalent compounds that hydrolyze in the presence of water. The trihaUdes form pyramidal molecules similar to the trivalent phosphoms analogues and may be prepared by direct combination of the elements. 

Esters of thioarsenious acid, As(SR)3 (R = Me, Et, Pr , Bu", Bu Ph), may be obtained by reacting alkali metal thiolates with arsenic halides (equation 9). In difficult cases (steric hindrance) more vigorous methods are used, e.g. (Bu S)3As (equation 10). 

Arsenic Phosphides.—Black or brown products of indefinite character, to which have been ascribed the formulae AsaP 4 and AsP,5 have been obtained by various methods, such as (1) by heating the elements together,6 (2) by allowing phosphorus to stand in solutions of arsenious acid,7 and (3) by the action of phosphine on arsenic halides.8 The properties of these substances resemble in general those which would be possessed by mixtures of the two elements thus, they burn in air to give the mixed oxides, decompose on heating with vaporisation of first phosphorus and then arsenic, and are oxidised by nitric acid. 

The catalyst is poisoned by CO, C02, and H20 so they must be rigorously removed upstream in the hydrogen synthesis process. Oxygen molecules are permanent poisons. Other poisons such as sulfur, arsenic, halides, and phosphorous must be carefully removed upstream in as much as they too are permanent poisons. 

All the arsenic trihalides are known compounds this is also tme for the rest of the group 15 cognates. Selected physical and molecular parameters for the arsenic halides are given in Table 2. ... 

The four arsenic halides are molecular compounds in the gas phase which have been shown by electron diffraction and microwave spectroscopy to have C3, pyramidal sfiuctures. ... 

Phosphorus and arsenic halides (Ph2PCl, PCI3, PBr3, and ASCI3) react with 62 in ether at low temperatures to form tetrazenides 67-70 (Table V) [Eqs. (87) and (88)]. Whereas 67 decomposes at higher temperatures (Table V) according to Eq. (89), 68 and 69 thermolyze even at room... 

The methyl arsenic system compromises two well-defined species, the pentamer (MeAs)5, a yellow pyrophoric oil (m.p. 12°C) and the purple black double-chain polymer, [(MeAs)2] (m.p. 204 °C). A red solid that is possibly the linear chain compound (MeAs) has also been described. The polymers are formed when samples of the pentamer are exposed to impurities like arsenic halides that are able to react with the arsenic-arsenic bond and may act as end groups. The most widely used method for the preparation of larger amounts of (MeAs)j is the reduction of methylarsonic acid, MeAsO(OH)2, or its sodium salt with hypophosphoric acid " °. Samples prepared by this method, however, may contain between 5 and 15% of impurities. A method that minimizes impurities is the reaction of MeAsHj with dibenzylmercury (equation 3) °. 

Reaction of organoantimony anionic species with phosphorus and arsenic halides... 

Reactions of Grignard reagents or organolithium compounds with arsenic halides, usually chlorides, have been one of the most frequently used method for the preparation of triorganoarsenic compounds. A wide variety of triorganoarsenic(III) compounds have been prepared as shown in equations 1 , 2 , 3 , 4 , 5 , 6 , 7 and 8 . 

Friedel-Crafts reaction of arsenic halides has been reported to give aromatic compounds as shown in equation 40 . Reactions with alkynes usually give mixtures of... 

Sulfur and selenium nucleophiles react with arsenic halides, amides and alkoxides to give the corresponding substituted products as shown in equations 154 155 156 , ... 

Primary and secondary arsines have also been used for reactions with arsenic halides (equations 193 ° and 194 ). 

Silyl and stannyl anions react with arsenic halides to give the corresponding As—Si and As—Sn compounds, respectively (equations 225 and 226 ). 

Symmetrical pentaorganoarsenic compounds have been synthesized from triorgano-arsenic halides R3ASX2 and tetraorganoarsenic halides R4ASX as shown in equations 284 and 285 . Tosylimine derivatives such as 37 have also been used for the preparation of pentaorganoarsenic compounds (equation 286 ). 

Reaction of arsenic halides with alkynes or aromatic compounds... 

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