Arsenic acid, reactions

Florvath D and Showalter K 1995 Instabilities in propagating reaction-diffusion fronts of the iodate-arsenous acid reaction J. Chem. Rhys. 102 2471-8... 

Fig. 1.17. Different forms of travelling wavefronts (a) travelling wavefront (propagating down tube) in iodate-arsenous acid reaction with excess iodate (b) travelling wavefront or pulse in iodate-arsenous acid reaction with excess arsenite (c) target patterns in Belousov-Zhabotinskii...

A different kind of computing device is a parallel machine that can also be implemented by means of macroscopic chemical kinetics. For this purpose we choose a bistable chemical reaction, the iodate-arsenous acid reaction ... 

Suppose we take 8 CSTRs, each run as shown in fig. 4.6 with the iodate-arsenous acid reaction, eq. (4.8). Each circle is a CSTR containing this bistable reaction. The arrows indicate tube connections among the 8 tanks through which the reaction fluid from one CSTR is pumped at a set rate into another CSTR. The widths of the lines are a qualitative measure of the rate of transport from one CSTR to another. Each isolated reactor can be in one of two stable stationary states 8 reactors can be in 2 such states. By our choice of the pumping rates we determine how many stable stationary states there are in the coupled reactor system. The dark (white) circles denote a state of high (low) iodide concentration. The choices of pumping rates and stable stationary states... 

Fig. 4.5 Plot of measured (I ) versus inflow rate coefficient in the iodate-arsenous acid reaction run in an open, well-stirred system, a CSTR. The arrows indicate observed transitions from one branch of stable stationary states to the other stable branch, as the inflow rate coefficient is varied, and define the hysteresis loop. (Taken from [21] with permission.)...

The evolution of iodide, I, in the iodate-arsenous acid reaction with arsenous acid in stoichiometric excess is well described by the RD equation... 

Prove (by analytical or numerical methods) that the (logarithm of the) steady state iodide concentration as a function of the (logarithm of) / H- is as shown in Fig. 4.3, if the kinetic differential equations of the iodate-arsenous acid reaction is to be taken... 

An examples of such systems in the gas phase is the illuminated reaction S2O6F2 = 2SO3F, [7]. An example of multiple stationary states in a liquid phase (water) is the iodate-arseneous acid reaction, [8]. Both examples can be analyzed effectively as one-variable systems. 

In Landolt -type reactions, iodate ion is reduced to iodide tlirough a sequence of steps involving a reductant species such as bisulfde ion or arsenous acid (H AsO ). The reaction proceeds through two overall... 

Arsenic(III) oxide is slightly soluble in water, giving a solution with a sweetish taste—but as little as 0.1 g can be a fatal dose (The antidote is freshly-precipitated iron(III) hydroxide.) The solution has an acid reaction to litmus, due to the formation of arsenic(III) acid ... 

Arsenic present only in traces (in any form) can be detected by reducing it to arsine and then applying tests for the latter. In Marsh s test, dilute sulphuric acid is added dropwise through a thistle funnel to some arsenic-free zinc in a flask hydrogen is evolved and led out of the flask by a horizontal delivery tube. The arsenic-containing compound is then added to the zinc-acid solution, and the delivery tube heated in the middle. If arsenic is present, it is reduced to arsine by the zinc-acid reaction, for example ... 

The synthesis can be carried out with most aromatic amines and is usually termed the Skraup reaction. The nitrobenzene is frequently replaced by arsenic acid, as in the prep)aration of 8-nitroquinoline from o-nitroanUine ... 

In view of the high reactivity and sensitivity to oxidation of o-phenylone-diamine, the normal experimental conditions of the Skraup reaction are modified the condensation is carried out hi the presence of glycerol, arsenic acid solution and dilute sulphuric acid. 

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)... 

Arsenic Peroxides. Arsenic peroxides have not been isolated however, elemental arsenic, and a great variety of arsenic compounds, have been found to be effective catalysts ia the epoxidation of olefins by aqueous hydrogen peroxide. Transient peroxoarsenic compounds are beheved to be iavolved ia these systems. Compounds that act as effective epoxidation catalysts iaclude arsenic trioxide, arsenic pentoxide, arsenious acid, arsenic acid, arsenic trichloride, arsenic oxychloride, triphenyl arsiae, phenylarsonic acid, and the arsenates of sodium, ammonium, and bismuth (56). To avoid having to dispose of the toxic residues of these reactions, the arsenic can be immobi1i2ed on a polystyrene resia (57). 

These precursors are prepared by reaction of fuming nitric acid in excess acetic anhydride at low temperatures with 2-furancarboxaldehyde [98-01-1] (furfural) or its diacetate (16) followed by treatment of an intermediate 2-acetoxy-2,5-dihydrofuran [63848-92-0] with pyridine (17). This process has been improved by the use of concentrated nitric acid (18,19), as well as catalytic amounts of phosphoms pentoxide, trichloride, and oxychloride (20), and sulfuric acid (21). Orthophosphoric acid, -toluenesulfonic acid, arsenic acid, boric acid, and stibonic acid, among others are useful additives for the nitration of furfural with acetyl nitrate. Hydrolysis of 5-nitro-2-furancarboxyaldehyde diacetate [92-55-7] with aqueous mineral acids provides the aldehyde which is suitable for use without additional purification. 

Bromide ndIodide. The spectrophotometric determination of trace bromide concentration is based on the bromide catalysis of iodine oxidation to iodate by permanganate in acidic solution. Iodide can also be measured spectrophotometricaHy by selective oxidation to iodine by potassium peroxymonosulfate (KHSO ). The iodine reacts with colorless leucocrystal violet to produce the highly colored leucocrystal violet dye. Greater than 200 mg/L of chloride interferes with the color development. Trace concentrations of iodide are determined by its abiUty to cataly2e ceric ion reduction by arsenous acid. The reduction reaction is stopped at a specific time by the addition of ferrous ammonium sulfate. The ferrous ion is oxidi2ed to ferric ion, which then reacts with thiocyanate to produce a deep red complex. 

In recent years, biochemists have developed an arsenal of reactions that are relatively specific to the side chains of particular amino acids. These reactions can be used to identify functional amino acids at the active sites of enzymes or to label proteins with appropriate reagents for further study. Cysteine residues in proteins, for example, react with one another to form disulfide species and also react with a number of reagents, including maleimides (typically A ethylmaleimide), as shown in Figure 4.11. Cysteines also react effectively... 

Reactions in aqueous solution can have complicated kinetics. An example Is the reaction between arsenic acid and iodide ions ... 

In the case of high concentrations of chromate and low concentrations of arsenous acid, we must take into account that dichromate ions are also involved in reaction. Thus... 

During the induced reduction of chlorate a considerable oxygen effect was observed. The air oxidation of arsenic(ril) is also an induced reaction, the extent of which decreases with increasing acid concentration and is increased by decreasing the rate of primary reaction. The induced oxidation caused by air also can be observed during the osmium tetroxide-catalyzed chlorate-arsenic(III) reaction. 

The presence of arsenous acid causes a considerable change in the induced reaction the error in the H2O2 determination decreases to a minimum and an As(ril) error appears, while the S2OI error remains practically unchanged. Though reaction between arsenic(III) and peroxydisulphate is about ten times as rapid as that between hydrogen peroxide and peroxydisulphate, the extent of the induced reduction of peroxydisulphate remains practically unchanged. This indicates that, in the induced chain oxidation, reaction (85), is replaced by the more rapid reaction... 

For arsenous acid oxidation, fundamental studies on the interplay of flow and reaction were made. By means of capillary-flow investigations, spatio-temporal concentration patterns were monitored which stem from the interaction of a specific complex reaction and transport of reaction species by molecular diffusion [68]. One prominent class of these patterns is propagating reaction fronts. By external electrical stimulus, electromigration of ionic species can be investigated. 

The arsenous acid-iodate reaction is a combination of the Dushman and Roebuck reactions [145]. These reactions compete for iodine and iodide as intermediate products. A complete mathematical description has to include 14 species in the electrolyte, seven partial differential equations, six algebraic equations for acid-base equilibriums and one linear equation for the local electroneutrality. 

OS 92] [R 32] [P 72/The iodate-arsenous acid reachon proceeds to one of two stationary states in different parts of the capillary when an electrical field of specific strength is applied [68]. Accordingly, a spatially inhomogeneous distribution of reaction products is generated along the capillary. 

Figure 4.101 Formation of zones due to the change of reaction mechanism by applying an electrical field during the oxidation of arsenous acid by iodate ( = 2.0 V cm" ). Numbers show the time intervals after the electric field was switched on. Intermediate product iodine (dark) and iodide (white) [68. ...

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