Arsenite,

Oxidation of As(III) by the silver(III) ion [Ag(OH)4] in alkaline solution occurs by parallel, second-order reactions of the three arsenite 

---

Arylarsonic acids are most readily prepared by the Bart Reaction, in which a diazonium salt in aqueous solution is run into a solution of sodium arsenite in an excess of sodium carbonate. The addition of copper sulphate to the +. ... 

Now add the diazonium solution slowly from a dropping-funnel to the vigorously-stirred arsenite solution, keeping the temperature of the latter at 5 7°. The frothing caused by the evolution of nitrogen will probably be dispersed by the stirrer if not, the addition of 1-2 ml. of ether, preferably in a fine jet from a wash-bottle, will cause it to subside. 

Methylene bromide (CHjBfj) and methylene iodide (CHjIj) are easily prepared by the reduction of bromoform or iodoform respectively with sodium arsenite in alkaline solution ... 

In a 1-litre three-necked flask, mounted on a steam bath and provided respectively with a separatory funnel, mechanical stirrer and double surface condenser, place 165 g. of bromoform (96 per cent.). Add 10 ml. of a solution of sodium arsenite made by dissolving 77 g. of A.R. arsenious oxide and 148 g. of A.R. sodium hydroxide in 475 ml. of water. Warm the mixture gently to start the reaction, and introduce the remainder of the sodium arsenite solution during 30-45 minutes at such a rate that the mixture refluxes gently. Subsequently heat the flask on the steam bath for 3-4 hours. Steam distil the reaction mixture (Fig. 11, 41, 1) and separate the lower layer of methylene bromide (79 g.). Extract the aqueous layer with about 100 ml. of ether a further 3 g. of methylene bromide is obtained. Dry with 3-4 g. of anhydrous calcium chloride, and distil from a Claisen flask with fractionating side arm. The methylene bromide boils constantly at 96-97° and is almost colourless. 

In a 1-litre three-necked flask, fitted with a mechanical stirrer, reflux condenser and a thermometer, place 200 g. of iodoform and half of a sodium arsenite solution, prepared from 54-5 g. of A.R. arsenious oxide, 107 g. of A.R. sodium hydroxide and 520 ml. of water. Start the stirrer and heat the flask until the thermometer reads 60-65° maintain the mixture at this temperature during the whole reaction (1). Run in the remainder of the sodium arsenite solution during the course of 15 minutes, and keep the reaction mixture at 60-65° for 1 hour in order to complete the reaction. AUow to cool to about 40-45° (2) and filter with suction from the small amount of solid impurities. Separate the lower layer from the filtrate, dry it with anhydrous calcium chloride, and distil the crude methylene iodide (131 g. this crude product is satisfactory for most purposes) under diminished pressure. Practically all passes over as a light straw-coloured (sometimes brown) liquid at 80°/25 mm. it melts at 6°. Some of the colour may be removed by shaking with silver powder. The small dark residue in the flask solidifies on cooling. 

Phenylarsonic acid may be obtained from the reaction between phenyl-diazonium chloride and sodium arsenite in the presence of a trace of copper sulphate ... 

The conversion of an aromatic diazonium compound into the corresponding arsonic acid by treatment with sodium arsenite in the presence of a catalyst, such as copper or a copper salt, is called the Bart reaction. A modification of the reaction employs the more stable diazonium fluoborate in place of the diazonium chlorid.i. This is illustrated by the preparation of />-nitrophenylarsonic acid ... 

Concurrently with the preparation of the phenyldiazonium chloride solution, prepare a cold suspension of sodium arsenite. Place 250 ml. of water in a 3-htre round-bottomed flask equipped with a mechanical stirrer. Heat the water to boding, add 125 g. of anhydrous sodium carbonate, and, as soon as the carbonate has dissolved, introduce 62 5 g. of pure arsenious oxide and 3 g. of crystallised copper sulphate with stirring. When all the solids have dissolved, cool the solution with stirring under a stream of tap water until the temperature has fallen to 15°. 

Alternatively, prepare the sodium meta-arsenite solution by dissolving 39 6 g. A.R. arsenious oxide and 32 g. of A.R. sodium hydroxide in 600 ml. of water. 

Azoxybenzene is readily prepared by reduction of nitrobenzene in an alkaline medium with dextrose or sodium arsenite ... 

Alkaline arsenite, O.IA As(lll) to As(V). Dissolve 4.9460 g of primary standard grade AsjOj in 40 mL of 30% NaOH solution. Dilute with 200 mL of water. Acidify the solution with 6N HCl to the acid color of methyl red indicator. Add to this solution 40 g of NaHC03 and dilute to 1 L. 

Iodine, Q.IN (0 to 1 —). Dissolve 12.690 g of resublimed iodine in 25 mL of a solution containing 15 g of KI which is free from iodate. After all the solid has dissolved, dilute to 1 L. If desired, check against a standard arsenite or standard thiosulfate solution. 

Make solution alkaline with NaHC03 and titrate excess I2 with standard arsenite solution. HPH2O2/4 = 16.499... 

The elements listed in the table of Figure 15.2 are of importance as environmental contaminants, and their analysis in soils, water, seawater, foodstuffs and for forensic purposes is performed routinely. For these reasons, methods have been sought to analyze samples of these elements quickly and easily without significant prepreparation. One way to unlock these elements from their compounds or salts, in which form they are usually found, is to reduce them to their volatile hydrides through the use of acid and sodium tetrahydroborate (sodium borohydride), as shown in Equation 15.1 for sodium arsenite. 

Arsenic is another element with different bioavailabiUty in its different redox states. Arsenic is not known to be an essential nutrient for eukaryotes, but arsenate (As(V)) and arsenite (As(III)) are toxic, with the latter being rather more so, at least to mammals. Nevertheless, some microorganisms grow at the expense of reducing arsenate to arsenite (81), while others are able to reduce these species to more reduced forms. In this case it is known that the element can be immobilized as an insoluble polymetallic sulfide by sulfate reducing bacteria, presumably adventitiously due to the production of hydrogen sulfide (82). Indeed many contaminant metal and metalloid ions can be immobilized as metal sulfides by sulfate reducing bacteria. 

The methods in which iodine is used as a catalyst for the reaction between ceric sulfate and nitrite or arsenite (86,87) are capable of determining smaH amounts of iodine. However, these catalytic methods are deHcate and require accurate timing, carefiH temperature control, and special apparatus. 

Methylene iodide [75-11-6], CH2I2, also known as diio dome thane, mol wt 267.87, 94.76% I, mp 6.0°C, and bp 181°C, is a very heavy colorless Hquid. It has a density of 3.325 g/mL at 20°C and a refractive index of 1.7538 at 4°C. It darkens in contact with air, moisture, and light. Its solubiHty in water is 1.42 g/100 g H2O at 20°C it is soluble in alcohol, chloroform, ben2ene, and ether. Methylene iodide is prepared by reaction of sodium arsenite and iodoform with sodium hydroxide reaction of iodine, sodium ethoxide, and hydroiodic acid on iodoform the oxidation of iodoacetic acid with potassium persulfate and by reaction of potassium iodide and methylene chloride (124,125). Diiodoform is used for determining the density and refractive index of minerals. It is also used as a starting material in the manufacture of x-ray contrast media and other synthetic pharmaceuticals (qv). 

Other salts include lead arsenates and lead arsenites (see Insect control technology), lead chromates and lead sihcochromates (see Pigments), lead cyanide (see Cyanides), lead 2-ethyIhexanoate (see Driers and metallic soaps), and lead fluoroborate (see Fluorine compounds, inorganic). 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

A widely used procedure for determining trace amounts of tellurium involves separating tellurium in (1 1) hydrochloric acid solution by reduction to elemental tellurium using arsenic as a carrier and hypophosphorous acid as reductant. The arsenic, reduced from an addition of arsenite to the solution, acts as a carrier for the tellurium. The precipitated tellurium, together with the carrier, is collected by filtration and the filter examined directly in the wavelength-dispersive x-ray fluorescence spectrometer. 

The soluble teUurites are more toxic than the selenites and arsenites. Hydrogen teUuride, formed by the action of water on aluminum teUuride [12043-29-7] Al2Te2, is a toxic gas (43). 

Arsenic Oxides and Acids. The only arsenic oxides of commercial importance are the trioxide and the pentoxide. These are readily soluble in alkaline solution, forming arsenites and arsenates, respectively. 

Arsenous Acids and the Arsenites. Arsenous acid [13464-58-9] AsH O, is known to exist only in solution. It is a weak acid with a... 

---