Halates

The alkali chlorates melt before decomposition [844], The catalytic properties of Co304 in promoting [865] the solid phase decomposition of NaC103 are attributed to the ability of the oxide to donate an electron to an oxygen atom, temporarily accepted at its surface from a CIO ion, prior to molecular oxygen formation and desorption. The progressive increase in E during reaction (from 120 to 200 kJ mole-1) is associated with systematic deactivation of the surface. 

The decomposition of Pb(C103)2 [868] (467—489 K) is complex, yielding both PbCl2 and PbO. Following an initial rapid deceleratory process, the sigmoid a—time curve for the main reaction obeyed the Prout-Tompkins equation [eqn. (9)] (0.35 a 0.85) with E = 180 kJ mole 1. AgC103 reacted [863] in a melt (589—612 K) with solidification at a 0.8 as the residual product (AgCl) accumulates (E = 239 kJ mole 1). The decomposition [826] of thallium(I) chlorate (423—443 K) may be 

Bancroft and Gesser [870] conclude that kinetic factors are predominant in determining whether decomposition of a metal bromate yields residual bromide or oxide. The thermal stabilities of the lanthanide bromates [877] and iodates [877,878] decrease with increase in cationic charge density, presumably as a consequence of increased anionic polarization. Other reports in the literature concern the reactions of bromates of Ag, Ni and Zn [870] and iodates of Cd, Co, Mn, Hg, Zn [871], Co and Ni [872], Ag [864], Cu [867], Fe [879], Pb [880] andTl [874]. 

A number of reactions of these compounds have received very great attention over many years. They have rates of a convenient magnitude for sampling methods, and the analytical properties of the systems simplify rate examination by at least one (usually rather non-specific) method. When the ready availability of the reactants, some intriguing rate phenomena (especially suitable for lecture demonstrations), early, though partial, success in their interpretation and a spice of controversy are added, the attention becomes explicable. 

The rate laws are complex, both for the forward reactions and, where studied, usually also for the back reactions. Some of the complexity is likely to be due to use of inadequate corrections for the activity coefficients just as some of the conflict is due to use of differing corrections. A more modern examination might clarify these points, since much of the work was published early in the period of application of the Debye-Hiickel theory. Correlation of the forms of the rate 

In Table 28 the probable rate laws for these reactions have been collected. They will be discussed separately below and major alternative forms mentioned. Note that several entries involve two or more terms, suggesting the corresponding 

Other (catalytic) terms have been recognised. 

The oxygen-stable cobalt(II)-cdta complex (H4cdta = trans-cyclo-hexane-l,2-diaminetetra-acetic acid) is oxidized by bromate ions. The [H ] dependence suggests a sequence of two steps  

These would be followed by release of B1O2 whose sequential reactions to Br2 are, in comparison, much faster. We note that the first intermediate might instead be a bromate complex, [(Hcdta)CoOBr02f , which could then release Br02 by further reaction with in a second step. 

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Reaction (11.4) is really a disproportionation reaction of the halate(I) anion 3XO 2X -E XO. ) Reaction (11.3) is favoured by the use of dilute alkali and low temperature, since the halate(I) anions, XO are thermally unstable and readily disproportionate (i.e. reaction (11.4)). The stability of the halate(I) anion, XO , decreases from chlorine to iodine and the iodate(I) ion disproportionates very rapidly even at room temperature. 

The stability of the halate(I) ion decreases, as expected, from C10 to 10 and only the chlorate(I) ion can be considered reasonably stable even in aqueous solution. Solid sodium bromate(I). NaBrO (with five or seven molecules of water of crystallisation) can be obtained, but on standing or warming it disproportionates ... 

Generally the solubility of a given metal halate decreases from chlorate(V) to iodatef and many heavy metal iodates(V) are quantitatively insoluble. Like their parent acids, the halates(V) are strong oxidising agents, especially in acid solution their standard electrode potentials are given below (in volts) ... 

Unexpectedly we find that the bromate(V) ion in acid solution (i.e. effectively bromic(V) acid) is a more powerful oxidising agent than the chlorate(V) ion, CIO3. The halates(V) are thermally unstable and can evolve oxygen as one of the decomposition products. Potassium chlorate(V), when heated, first melts, then resolidifies due to the formation of potassium chlorate(VII) (perchlorate) ... 

Ha.la.tes, Silver chlorate, AgClO, silver bromate, AgBrO, and silver iodate, AglO, have been prepared. The halates may decompose explosively if heated. 

Bromocresol purple (5.2...6.8) glutamic and ketoglutaric acids [217], halide and halate anions [91,218, 219] preservatives [220, 221] products of pyrolysis of epoxy resins [222] 5-aminodibenzocyclo-heptane derivatives [223] phenylalkanolamines, eph-edrine [224]... 

Other oxoacid salts of the alkali metals are discussed in later chapters, e.g. borates (p. 205), silicates (p. 347), phosphites and phosphates (p. 510), sulfites, hydrogensulfates, thiosulfates, etc. (p. 706) selenites, selenates, tellurites and tellurates (p. 781), hypohalites, halites, halates and perhalates (p. 853), etc. 

Halic acids HOClOi H0Br02 HOIO2 Halates... 

However, only one-sixth of the halogen present is oxidized and alternative routes are more generally preferred for large-scale manufacture. Thus, the most important halate, NaC103, is manufactured... 

The modes of thermal decomposition of the halates and their complex oxidation-reduction chemistry reflect the interplay of both thermodynamic and kinetic factors. On the one hand, thermodynamically feasible reactions may be sluggish, whilst, on the other, traces of catalyst may radically alter the course of the reaction. In general, for a given cation, thermal stability decreases in the sequence iodate > chlorate > bromate, but the mode and ease of decomposition can be substantially modified. For example, alkali metal chlorates decompose by disproportionation when fused ... 

For all three halates (in the absence of disproportionation) the preferred mode of decomposition depends, again, on both thermodynamic and kinetic considerations. Oxide formation tends to be favoured by the presence of a strongly polarizing cation (e.g. magnesium, transition-metal and lanthanide halates), whereas halide formation is observed for alkali-metal, alkaline- earth and silver halates. 

The oxidizing power of the halate ions in aqueous solution, as measured by their standard reduction potentials (p. 854), decreases in the sequence bromate > chlorate > iodate but the rates of reaction follow the sequence iodate > bromate > chlorate. In addition, both the thermodynamic oxidizing power and the rate of reaction depend markedly on the hydrogen-ion concentration of the solution, being substantially greater in acid than in alkaline conditions (p, 855). 

An important series of reactions, which illustrates the diversity of behaviour to be expected, is the comproportionation of halates and halides. Bromides are oxidized quantitatively to bromine and iodides to iodine, this latter reaction being much used in volumetric analysis ... 

The greater thermodynamic stability of iodates enables iodine to displace CI2 and Bt2 from their halates ... 

The various reactions of bromates and iodates are summarized in the. schemes on p. 866. The oxidation of halates to perhalates is considered further in the next section. 

As with FCIO2 and FIO2, hydrolysis regenerates the halate ion, the reaction with FBr02 being of explosive violence. Hydrolysis in basic solution at 0° can be represented as... 

When the solution was acidified the disulfide again separated, but the solution also contained the thiol, and, therefore, these investigators supposed that the reaction had proceeded to form an analog not only of a halite but also of a halate [Eq. (9)]. The existence of the... 

The stabilities of the ammonium halates increase in the sequence NH4Br03 < NH4CIO3 < NH4IO3 [940]. Decompositions of the chlorate... 

The trivalent [P04] and [As04] ions react similarly. Examples of anions that give insoluble Hg(I) compounds in this way include halides, pseudohalides, halates, carboxylates and sulfate. A trace of HNO3 or HCIO4 is often added to the solution of the Hg(I) nitrate or perchlorate to prevent disproportionation induced by alkali. Table 1 lists common Hg(I) derivatives prepared in this way and includes values of the solubility products of the sparingly soluble Hg(I) compounds where these are measured. A similar reaction is used to prepare HgjCO, from a soluble bicarbonate ... 

Studies of the intoxicating effects of toluene showed that the inhalation of its vapor at a concentration of 200 ppm was associated with the development of mild-to-moderate intoxication, characterized by sedation, paresthesias, and hyporeflexia. Toluene vapor concentrations of 600-800 ppm induced a confusional state, whereas greater concentrations produced an intense euphoria (Benignus 1981 Press and Done 1967). In humans, plasma concentrations of toluene of 10-100 pM have been reported to be intoxicating these concentrations are close to the intoxicating concentrations of alcohol and in-halational anesthetics (Miller 1985). 

Habituating drugs 76 Halate anions 45 Halide anions 45 Halogen anions 231, 232 Halogen acids 189... 

When microscopists began to look at the tissues of living forms they already had in their minds a view of matter as an aggregate of more or less uniform microscopic components. It is therefore understandable that when they saw everywhere agglomerations of more or less spherical halations, they concluded that these optical illusions were the fundamental subunits of animate matter, and when they actually saw cells they had no idea what they were (Harris, 1999, p. 39-... 

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