Reaction with arsenic

Figure 2. Mechanism of dihydroxyacetone/arsenate reaction with FDP aldolase. Both dihydroxyacetone and inorganic arsenate are not the inhibitor of the aldolase reactions. The rate constant for the arsenate ester formation is determined enzymatically (a plot of 1/v vs 1/E gives a non-zero intercept which is attributed to the rate at infinite enzyme concentration and that rate corresponds to the rate of nonenzymatic formation of the arsenate ester).

Spectrophotometric methods using Na-DDTC are rather insensitive since the colours of metal complexes with DDTC are not intense. Complexes with Cu, Bi, and Mn are among the most intensely coloured diethyl dithiocarbamates. The yellowish Ag-DDTC is used in the determination of arsenic (reaction with ASH3, see Section 8.2.2). Fig. 19.1 shows the absorption spectra of some metal diethyldithiocarbamates. 

Powerful oxidising agents, for example Cv20Y and MnO ions, oxidise the arsenate(III) ion to arsenate(V). The reaction with iodine, however, is reversible depending on the conditions ... 

The success of the Bart reaction when applied to nuclear- substituted anilines is often much affected by the pH of the reaction-mixture. Furthermore, the yields obtained from some m-substituted anilines, which under the normal conditions are usually low, arc considerably increased by the modifications introduced by Scheller, and by Doak, in which the diazotisation is carried out in ethanolic solution followed by reaction with arsenic trichloride in the presence of a cuprous chloride or bromide catalyst. 

Hexafluoroarsenic acid [17068-85-8] can be prepared by the reaction of arsenic acid with hydrofluoric acid or calcium fluorosulfate (29) and with alkaH or alkaline-earth metal fluorides or fluorosulfonates (18). The hexafluoroarsenates can be prepared directly from arsenates and hydrofluoric acid, or by neutrali2ation of HAsF. The reaction of 48% HF with potassium dihydrogen arsenate(V), KH2ASO4, gives potassium hydroxypentafluoroarsenate(V)... 

Xeaoa difluoride behaves as a fluoride ioa doaor toward many metal pentafluorides to form complex salts containing the XeF" and Xe2F" 2 cations (10). In reactions with the pentafluorides of arsenic, antimony, and mthenium, for example, it forms the salts Xe2F" 2AsF(, [21308-45-2], XeF" AsF(, [26024-71-5], [12528-47-1], XeF+Sbp-g [36539-18-1], [17679-45-7], [15364-10-0], [36539-19-2], [26297-25-6],... 

Arsenic trifluoride (arsenic(III) fluoride), AsF, can be prepared by reaction of arsenic trioxide with a mixture of sulfuric acid and calcium fluoride or even better with fluorosulfonic acid. Chlorine reacts with ice-cold arsenic trifluoride to produce a hygroscopic soHd compound, arsenic dichloride trifluoride [14933-43-8] ASCI2F35 consisting of AsQ. and AsF ions (21). Arsenic trifluoride forms a stable adduct, 2AsF2 SSO, with sulfur trioxide and reacts with nitrosyl fluoride to give nitrosonium hexafluoroarsenate(V) [18535-07-4] [NO][AsFg]. 

Arsenic trichloride (arsenic(III) chloride), AsQ. is the most common and important haUde of arsenic. It may be formed by spontaneous combination of the elements and, in addition, by the following reactions (/) chlorine with arsenic trioxide (2) sulfur monochloride, 82(11, or a mixture of S2CI2 chlorine, with arsenic trioxide and (J) arsenic trioxide with concentrated hydrochloric acid or with a mixture of sulfuric acid and a chloride. 

Methylarsine, trifluoromethylarsine, and bis(trifluoromethyl)arsine [371-74-4] C2HAsF, are gases at room temperature all other primary and secondary arsines are liquids or solids. These compounds are extremely sensitive to oxygen, and ia some cases are spontaneously inflammable ia air (45). They readily undergo addition reactions with alkenes (51), alkynes (52), aldehydes (qv) (53), ketones (qv) (54), isocyanates (55), and a2o compounds (56). They also react with diborane (43) and a variety of other Lewis acids. Alkyl haUdes react with primary and secondary arsiaes to yield quaternary arsenic compounds (57). 

The Bart reaction is successful with a wide variety of aromatic and heterocycHc amines. A variation in which an aromatic amine, in the presence of arsenic trichloride, is dia2oti2ed in an organic solvent (the ScheUer reaction) has also found wide appHcation. Both arsonic and arsinic acids can be prepared by the ScheUer reaction which often gives better yields than the Bart reaction with electron-attracting substituents on the aromatic ring. For the commercial preparation of 4-aminophenylarsonic acid [98-50-0] (arsaniUc acid), C HgAsNO, and 4-hydroxyphenylarsonic acid [98-14-6] C H AsO, the Bnchamp reaction is used ... 

Trimethylarsine gives a 98% yield of trimethylarsine difluoride when treated with xenon difluoride [102] in fluorotrichloromelhane. and tnsfpentafluorophen-yl)arsine gives a 94% yield of tris(pentafluornphenyl)arsme difluoride after reaction with dilute fluorine in fluorotnchloromethane at 0 C [106] Other trivalent arsenic compounds have also been fluorinated with xenon difluoride [103] In addition, arsines have been oxidatively fluorinated by iodine pentafluoride [107] or electrochemically in 26-34% yield [108]... 

Carbon disulfide gives an essentially quantitative yield of carbon tetralluoride and sulfur on reaction with sulfur tetrafluoride at 450 C in the presence of arsenic trifluoride as a catalyst. At lower temperature, bis(fnfiuoromethyl) polysulfides are formed [//] (equation 15). 

E. Reactions with Sulfui , Selenium, Tellurium, Phosphorus, and Arsenic Derivatives.. . 171... 

E. Reactions with Sulfur, Selenium, tellurium. Phosphorus, AND Arsenic Derivatives... 

It is striking that reactions of arsenic(III) with 1-equivalent oxidizing agents take place fairly slowly, while reactions with 2-equivalent partners e.g. with iodine, are fast. To interpret this behaviour it was suggested by Waters that arsenious acid has the tautomeric forms... 

Synopsis of dangerous reactions with arsenic and derivatives... 

Finally, anions that are incompatible with oxidants will give rise to violent reactions with iodates. This goes for cyanides, thiocyanates and sulphides. In the last case, arsenic, antimony, copper and tin sulphides were the main ones cited. 

The most general method for the simultaneous analysis of oxyanions by gas chromatography is the formation of trimethylsilyl derivatives. Trimethylsilyl derivatives of silicate, carbonate, oxalate, borate, phosphite, phosphate, orthophosphate, arsenite, arsenate, sulfate and vanadate, usually as their ammonium salts, are readily prepared by reaction with BSTFA-TMCS (99 1). Fluoride can be derivatized in aqueous solution with triethylchlorosilane and the triethylfluorosilane formed extracted into an immiscible organic solvent for analysis by gas chromatography [685). 

Figures 3 and 4 show the amounts of arsenate sorbed onto ferrihydrite and Al(OH)x after 24 hrs of reaction with a surface coverage of arsenate and phosphate respectively of 50 or 100%. The numbers in parenthesis indicate the efficiency (in percentage) of phosphate in preventing sorption of arsenate calculated according to the expression of Deb and Datta (1967). 

Reactions of Phosphorus and Arsenic Ylides with Organocyclosilthianes and... 

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