Arsenic anions

It is of interest to mention that in the presence of small amounts of sodium phosphate or arsenate the formation of 69 becomes the dominant reaction at pH 6.0 and 50°C the ratio 69/68 is 90/10. The strong catalytic effect of the phosphate and arsenate anions on the rate of formation of the ethano derivative 69 bears some analogy to the semicarbazone formation between ketone and amine, which is also found to be effectively catalyzed by these anions (68JA4319). 

Waychunas, G.A. fuller, C.C. Davis, J.A. Big-ham, J.M. Schwertmann, U. (1995a) EX-AFS and simulation study of selenate and arsenate anion positions in coprecipitated schwertmannites. Abstract Amer. Geophys. Union... 

Pookrod, P., Haller, K.J. and Scamehorn, J.F. (2004) Removal of arsenic anions from water using polyelectrolyte-enhanced ultrafiltration. Separation Science and Technology, 39(4), 811-31. 

Condensed arsenic anions are much less stable than the condensed phosphates and, owing to rapid hydrolysis, do not exist in aqueous solution. Dehydration of KH2As04 gives three forms, stable at different temperatures, of metaarsenate one form is known to contain an infinite chain polyanion, and another contains the cyclotriarsenate ion, [As309]3 . 

Molybdenum, in particular, is known to form a very large number of structurally diverse polyanions in assodation with other oxo ligands such as squarate (C404 ), methoxide, malate, phosphate, and arsenate anions.7 Space does not permit discussion of this plethora of interesting compounds, nor of still others. We shall focus mainly on the so-called classic polymolybdates and polytungstates. 

Reaction of group 15 elements like arsenic with alkali or alkaline earth metals forms Zintl anions of the general type Asn". Characterization of these species has been accomplished dissolving the solids in liquid NH3 or ethylenediamine (H2NCH2CH2NH2) and adding the macrocycle, 2,2,2-crypt (5) to complex the cations and stabilize the polyatomic anions. The fully characterized Zintl arsenic anions As4, As and Asu are shown inFigme 1. ... 

Figure 11 Arsenic-rich chalcogenide anions related to Asn. [AsioEs] ions (35) found in [PPh4]2[AsioSe3], [PPh4]2[AsioTe3], and [K(2,2,2-cryptand)]2[AsioS3] and the chalcogen-poorest arsenic anion [AsnTe] (36) in [K(2,2,2-cryptand)]3[AsnTe] en ...

So-called capped Keggin structures were first observed with the vanadophosphate and -arsenate anions, [(T)V14042]9-. These anions contain an o-Keggin core to which are attached two V03+ groups, as shown in Figure 7. The phosphate anion has received the most attention.116 In 0.6 M Na(Cl) at 1.3 < pH 4.0, the major solute species is [H4PV 4042] and the transient existence of... 

Early polarographic studies of the (a) molybdodiphosphate and -arsenate anions showed that upon reduction they were slowly transformed into / isomers in an analogous manner to the behavior of the corresponding Keggin molybdates.143 It has been reported, however, that the P-NMR spectrum of a reduced /3 -[P2Mo18062] has one line which is consistent only with an a -, 7-, or 7 -structure.136... 

Isolated pyramidal arsenic anions with sulfur and selenium of the type M3ASE3 (M = Na, K, Tl E = S and... 

The above example reveals that the activity of respiratory arsenate reducers can be elicited when arsenate anions are present at high concentrations ( 10... 

The hexacoordinate arsenate anion (28) is prepared by condensing the salt (95) with 2,2 -dilithiobiphenyl (Equation (41)). Diastereomeric Brucine salts are prepared that can be crystallized to give optically active derivatives of the anion (28) <67LA(705)66>. 

D. T. Malotky and M. A. Anderson, Hie adsorption of the potential determining arsenate anion on oxide surfaces. Colloid Interface Sci. 4 281 (1976). M. A. Anderson and D. T. Malotky, The adsorption of protolyzable anions on hydrous oxides at the isoelectric pH, J. Colloid Interface Sci. 72 413 (1979). 

Figure 6.13 Speciation of arsenic anions. Allsep anion column, 100x4.5 mm. Mobile phase 4 mM lithium p-hydroxy-benzoate, pH 8.5. Conductivity detection. Peaks (1) arsenite, (2) arsenate (courtesy Alltech).

The reduction is accelerated by heating. It takes place only in strongly acid solution, since only arsenic cations or undissociated arsenic hahdes react with stannous chloride. In weakly acidified solutions, arsenic anions are present but no cations, because of the hydrolysis ... 

Similar to reactions with arsenic selenide anions described in the previous section, pentacarbonyliron or the hydrido-iron tetracarbonyl anion react with arsenic tellurides to produce complex iron carbonyl-bound tellurium arsenic anions (Scheme 85). Unlike the selenium analogs, the isolated complex for Te does not exhibit Fe-As bonds. 

A modified nonpolar stationary phase and UV detection was used for the separation of arsenic species [45]. Unfortunately, little real sample work was performed. Recently, a nonsuppressed IC method for the separation of various organic arsenic anions was reported by Hirayama and Kuwamoto [46]. 

D.S. Bushee, I.S. Krull, PR. Demko, and S.B. Smith, Jr. Trace analysis and speciation for arsenic anions by HPLC-hydride generation-inductively coupled plasma emission spectroscopy. J. Liquid Chrom., 7(5), 8671 (1984). 

Arsenic anions converted to 2,3 mercaptopropanol complexes, then GLC 0.2ng (AsOj AsO,4) 0.04ng (monomethyl arsenic acid [794]... 

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