Antimony and Arsenic

Accurate kinetic data for the reactions of benzyl, cyclohexyl, r-butyl, l-(l-diethylamino)ethyl, and 2-(2-hydroxy)propyl radicals with oxygen in the liquid phase have been reported by Scaiano et who find that, 

The reaction between the hydrated electron and O3 in bicarbonate-containing solution at pH 9 gives O3 with a rate constant of (3.60 0.2) x 10 liter moP s with routes via O (formed by deprotonation of OH), O2 or O being ruled out. Peroxy radical [formed from e (aq) and O2] reacted with O3 to give O3 and O2 stoichiometrically, with a rate constant at pH 10.3 of (1.52 0.05) x 10 liter moP s From competition studies involving H with O3 and O2, the rate constant for the H/O3 reaction at pH 2 was estimated to be (3.65 0.4) x 10 liter mol s.  

The kinetic and mechanistic aspects of the reaction of ozone with olefins and acetylene in the liquid phase have been extensively 

The kinetics of O2 protonation in EtOH and H2O have been studied. The dismutation of O2 to H2O2 and O2 is catalyzed by Fe(II) and Fe(III) complexes.A value of the pX for HO2 of 4.8 0.05 is proposed by different workers who studied the formation and decay kinetics of O2 and HO2 generated by pulse radiolysis,and obtained a value for 2k (HO2 + HO2) of (3.7 0.2) X 10 liter mol s in the pH range 1.5-8 and for 2k (O2 +O2) 10 liter moP s O2 may also be generated from alkaline H202/ The kinetics and mechanisms of reactions of O2 and ethyl acetate,ascorbic acid, and dehydroascorbic acid have been reported. 

Using purified alkali and chelating agents to control catalytic processes, Galbacs and Csanyi have estimated a rate constant for the noncatalyzed alkali-induced decomposition of H2O2 at pH 11.6 and 308 K of 3 x 

Whereas nitrogen and phosphorus were both nonmetals, arsenic (As) and antimony (Sb) are both metalloids. Although phosphorus is normally found in minerals, arsenic and antimony are more often found as sulfides in nature and in significantly smaller quantities. Pure samples of each metalloid are usually dark gray in color. 

One of the most common applications for these two metalloids is for use when strengthening alloys, or mbrtures of elements, especially lead. Lead is a relatively soft, dense metal, so to make lead harder for applications such as bullets, either metalloid can be added to help make the resulting product stronger. This practice of alloying arsenic and antimony with lead dates back to the Bronze Age. 

Another use for arsenic is as a poison, sometimes for good in the cases of pesticides and insecticides and sometimes for bad in the cases of chemical warfare and homicides. As a chemical warfare agent, arsenic s role as a rainbow herbicide is most likely the most horrific. Similar to the well-known Agent Orange, Agent Blue (another rainbow herbicide) was a chemical used in the Vietnam war to destroy plants, serving to both destroy the enemies  

Arsenic poisoning is a serious concern in areas with naturally contaminated water supplies, such as Bangladesh s ground water. Some estimates are as high as 20 percent of all wells around the world suffer some sort of arsenic contamination, which can lead to both skin and bladder cancers (and ultimately death). 

A mixture of chromium, copper, and arsenic (known as CCA) has been used for many decades as a wood preservative you can usually tell if wood has been treated by CCA as it will have a light-greenish tint. The use of CCA as a preservative is slowly being phased-out, however, due to concerns that acidic environments (such as acid rain, for example) could cause the arsenic to leach out of the wood and into the environment. 

Several papers have appeared on the mechanism of decomposition of ozone in aqueous solution. A chain mechanism is proposed for the oxidation of saturated alcohols by O3 in aqueous solution. Acetic acid and acetate ion are knwn to stabilize ozone in aqueous solution, possibly due to their ability to scavenge the hydroxyl radical. A pulse radiolysis studyof the reaction of O3 with CH2C00 leads to the mechanism involving reactions (40)-(44). Reactions of 

Oj have been studied in toluene solution of the potassium 18-crown-6 salt. With spin traps adducts are observed mainly derived from 0 , derived from reaction (45). Reactions of superoxide, Oj, with ascorbic acid involve deprotonation 

Satchell and Satchell have continued their studies on the mechanisms of reactions of thio compounds. The Ag -catalyzed hydrolysis of thioacetates occurs by pathways involving one and two silver ions respectively bound to the sulfur of the thioacetal. In the hydrolytic decomposition of disulfides, shown in equation (52), the mechanism can involve a species R2S2Ag2 , with both silver ions 

The boron trifluoride catalyzed reaction of ArN(R)SPh with RC=CR involves the formation of the intermediate (13). The reaction of 

A rather detailed study of the reaction between thiourea and bromine in the pH range 1.5-4 has appeared/ and the mechanism is set out in reactions (55)-(58). Three separate intermediates are postulated. In addition to this, reaction (57) can occur by an additional pathway catalyzed by bromide ion. This is certainly a much more complex system than the reaction of I2 with thiourea, where the established product is (NH2 CSSC(NH2)i. Buxton has published a study of the oxidation of SCN and of 1 by H to form (SCN)2 and IJ, respectively. The species HSCN is a precursor in the former case. The spectrum of HP could not be detected. In concluding this section, we note a theoretical study of the regioseleCtive addition of dicyanoacetylene to S4N4. 

Mechanisms of reactions of five- and six-co-ordinate compounds, e.g. PFs and PFe , will be discussed with the exactly analogous arsenic and antimony compounds in the following section on those elements. 

Arsenic and Antimony. Three studies of reaction mechanisms for tetrahedral antimony(v) compounds are reported. These are of the reaction of trimethylantimony sulphide (MegSbS) with alkyl halides, where a four-centre transition state seems possible, the reaction of R4Sb+ cations with alkoxide ions, and the ageing of antimonic acid in aqueous solution. Both thermal and photochemical decomposition of pentaphenylanti-mony have been investigated. Whereas the products of the photochemical reaction are numerous, though all derived from phenyl radicals, the 

Five- and six-co-ordinate compounds, of phosphorus as well as of arsenic and antimony, are linked by a qualitative study of fluorine exchange in a wide variety of systems. Whether this exchange was slow or fast was determined for eighteen combinations of compounds by F n.m.r. spectroscopy. Fluorine exchange is fast when fluorine bridges between compounds can be formed, as in well-known cases involving, e.g., Sb—F—Sb bridges and in newly established cases such as P—F—Sb and As—F—As.  

Hydrolysis of SbClg is not acid-catalysed. The difference between MCle and MFg in these Group V complexes exactly parallels that of octahedral transition-metal complexes, e.g. c/5 -[Coen2F2]+ and cis-[Co enaCla] . But rates of hydrolysis of SbClg in alkaline solution are a function of hydroxide ion concentration. Presumably there is associative attack by hydroxide ion since SbClg has no acidic protons to permit an iS Nlcb mechanism. The kinetic pattern here is complicated by the presence of the buffers used, for these can and do complex with the antimony. 

Hydrolysis of complexes of the type MFe is catalysed not only by acid but also by a series of metal ions. Kinetic data have been obtained for catalysis of hydrolysis of PFe, AsFg , AsFgCOH)- and also of BF4-, by beryllium(ii), aluminium(iii), zirconium(iv), and thorium(rv). Again this may be seen as an extension of studies on cation catalysis of hydrolysis of transition-metal complexes, e.g. the numerous studies of mercury(ii)-catalysed aquations of cobalt(iii)-ammine-halide complexes, or the recent study of metal ion catalysis of chloro(ethylenediaminetriacetato)-cobaltate(m).  

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Crude lead contains traces of a number of metals. The desilvering of lead is considered later under silver (Chapter 14). Other metallic impurities are removed by remelting under controlled conditions when arsenic and antimony form a scum of lead(II) arsenate and antimonate on the surface while copper forms an infusible alloy which also takes up any sulphur, and also appears on the surface. The removal of bismuth, a valuable by-product, from lead is accomplished by making the crude lead the anode in an electrolytic bath consisting of a solution of lead in fluorosilicic acid. Gelatin is added so that a smooth coherent deposit of lead is obtained on the pure lead cathode when the current is passed. The impurities here (i.e. all other metals) form a sludge in the electrolytic bath and are not deposited on the cathode. 

Arsenic and antimony resemble phosphorus in having several allotropic modifications. Both have an unstable yellow allotrope. These allotropes can be obtained by rapid condensation of the vapours which presumably, like phosphorus vapour, contain AS4 and Sb4 molecules respectively. No such yellow allotrope is known for bismuth. The ordinary form of arsenic, stable at room temperature, is a grey metallic-looking brittle solid which has some power to conduct. Under ordinary conditions antimony and bismuth are silvery white and reddish white metallic elements respectively. 

In addition to the trihalides, arsenic and antimony form penta-fluorides and antimony a pentachloride it is rather odd that arsenic pentachloride has not yet been prepared. 

Nitrogen is unusual in forming so many oxides. The acidity of the Group V oxides falls from phosphorus, whose oxides are acidic, through arsenic and antimony whose oxides are amphoteric, to the basic oxide ofbismuth. This change is in accordance with the change from the non-metallic element, phosphorus, to the essentially metallic element, bismuth. The +5 oxides are found, in each case, to be more acidic than the corresponding + 3 oxides. 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

The standard electrode potential for zinc reduction (—0.763 V) is much more cathodic than the potential for hydrogen evolution, and the two reactions proceed simultaneously, thereby reducing the electrochemical yield of zinc. Current efficiencies slightly above 90% are achieved in modem plants by careful purification of the electrolyte to bring the concentration of the most harmful impurities, eg, germanium, arsenic, and antimony, down to ca 0.01 mg/L. Addition of organic surfactants (qv) like glue, improves the quaUty of the deposit and the current efficiency. 

The oxidation of methacrolein to methacrylic acid is most often performed over a phosphomolybdic acid-based catalyst, usually with copper, vanadium, and a heavy alkaU metal added. Arsenic and antimony are other common dopants. Conversions of methacrolein range from 85—95%, with selectivities to methacrylic acid of 85—95%. Although numerous catalyst improvements have been reported since the 1980s (120—123), the highest claimed yield of methacryhc acid (86%) is still that described in a 1981 patent to Air Products (124). 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

Iron, copper, arsenic, and antimony can be readily removed by the above pyrometaHurgical processes or variations of these (3). However, for the removal of large quantities of lead or bismuth, either separately or together, conventional electrolysis or a newly developed vacuum-refining process is used. The latter is now in use in Austraha, BoHvia, Mexico, and the CIS (5). 

Analysis of zinc solutions at the purification stage before electrolysis is critical and several metals present in low concentrations are monitored carefully. Methods vary from plant to plant but are highly specific and usually capable of detecting 0.1 ppm or less. Colorimetric process-control methods are used for cobalt, antimony, and germanium, turbidimetric methods for cadmium and copper. Alternatively, cadmium, cobalt, and copper are determined polarographicaHy, arsenic and antimony by a modified Gutzeit test, and nickel with a dimethylglyoxime spot test. 

A process has been developed to recover antimony and arsenic from speiss and other materials (11). The speiss is roasted along with a source of sohd sulfur and coal or coke at a temperature of 482—704 °C for a sufficient time to volatilise arsenic and antimony oxides. The arsenic can then be separated from the antimony through careful control of the off-gas temperature and oxygen potential (12). 

G. T. Morgan, Organic Compounds of Arsenic and Antimony, Longmans, Green and Co., London, UK, 1918. 

In a manner similar to phosphoms, arsenic, and antimony, the bismuth atom can be either tri- or pentacovalent. However, organobismuth compounds are less stable thermally than the corresponding phosphoms, arsenic, or antimony compounds, and there are fewer types of organobismuth compounds. For example, with R MX, R3MX2, R2MX3, and RMX, where M is a Group 15 (VA) element and X is a halogen, only the first two types have been prepared where M = Bi, but all four types are known where M = P, As, or Sb. 

Although trialkyl- and triarylbismuthines are much weaker donors than the corresponding phosphoms, arsenic, and antimony compounds, they have nevertheless been employed to a considerable extent as ligands in transition metal complexes. The metals coordinated to the bismuth in these complexes include chromium (72—77), cobalt (78,79), iridium (80), iron (77,81,82), manganese (83,84), molybdenum (72,75—77,85—89), nickel (75,79,90,91), niobium (92), rhodium (93,94), silver (95—97), tungsten (72,75—77,87,89), uranium (98), and vanadium (99). The coordination compounds formed from tertiary bismuthines are less stable than those formed from tertiary phosphines, arsines, or stibines. 

Lead, arsenic, and antimony—determined in the solution obtained by boiling 10 g of the titanium dioxide for 15 min in 50 mL of 0.5 Nhydrochloric acid In addition to individual specifications, general specifications have been written for provisionally Hsted certifiable colors ... 

Impurities ate elirninated in fire refining in the foUowing sequence slag, that is, oxides of iron, magnesium, aluminum, and sihcon fluxing, that is, arsenic and antimony and vapors, that is, sulfur (as SO2), cadmium, and zinc. 

Lead The production of lead from lead sulphide minerals, principally galena, PbS, is considerably more complicated than the production of zinc because tire roasting of the sulphide to prepare the oxide for reduction produces PbO which is a relatively volatile oxide, and therefore the temperature of roasting is limited. The products of roasting also contain unoxidized galena as well as die oxide, some lead basic sulphate, and impurities such as zinc, iron, arsenic and antimony. 

C. A. McAuliffe and W. Levason, Phosphine, Arsine and Stibine Complexes of the Transition Elements, Elsevier, Amsterdam, 1979, 546 pp. A review with over 2700 references. See also C. A. McAuliffe (ed,), Transition-Metal Complexes of Phosphorus, Arsenic and Antimony Donor Ligands, Macmillan, London, 1972,... 

C. A. McAuliffe (ed.), Transition Metal Complexes of Phosphorus, Arsenic and Antimony Ligands, Macmillan, London, 1973, 428 pp. 

In situations such as the acid pickling of steel or the use of steel pipes to handle sour oil streams, the use of suitable inhibitors can give a significant reduction in hydrogen entry. In this context it is important to emphasise that the efficiency of an inhibitor in reducing hydrogen entry is not the same as its efficiency in reducing corrosion. Thus arsenic and antimony compounds... 

Procedure. Place 80 mL of the arsenic/antimony solution in the titration cell of the spectrophotometer. Titrate with standard bromate/bromide solution at 326 nm taking an absorbance reading at least every 0.2 mL. From the curve obtained calculate the concentration of arsenic and antimony in the solution. 

Phosphorus, arsenic and antimony complexes of the main group elements. W. Levason and C. A. McAuliffe, Coord. Chem. Rev., 1976,19,173-185 (88). 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

The radii in the lowest row of the table were obtained by a number of approximate considerations. For instance, if we assume the bismuth radius to bear the same ratio to the interatomic distance in elementary bismuth as in the case of arsenic and antimony, we obtain (Bi) = 1.16— 1.47 A. A similar conclusion is reached from a study of NiSb and NiBi (with the nickel arsenide structure). Although the structures of the aurous halides have not been determined, it may be pointed out that if they are assumed to be tetrahedral (B3 or Bi) the interatomic distances in the chloride, bromide, and iodide calculated from the observed densities1) are 2.52, 2.66, and 2.75 A, to be compared with 2.19, 2.66, and 2.78 A, respectively, from pur table. 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

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