Redox reactions antimony

Buchanan and co-workers studied the behavior of various aromatic compounds in antimony(III) molten salts [30]. These salts can act both as mild Lewis acids and allow redox reactions to take place. The Lewis acidity of the melt can be tuned by controlling the concentration of [SbCl2]. Basic melts are formed by addition of a few mol % of a chloride donor such as KCl, whereas acidic melts are formed by addition of chloride acceptors such as AICI3 (Scheme 5.1-11). 

A total of 0.8 gram of elemental antimony was isolated from the distillation residue in flask I, indicating that only a minor redox reaction had occurred. 

Unstabilized chrome yellow pigments have poor lightfastness, and darken due to redox reactions. Recent developments have led to improvements in the fastness properties of chrome yellow pigments, especially toward sulfur dioxide and temperature. This has been achieved by coating the pigment particles with compounds of titanium, cerium, aluminum, antimony, and silicon [3.134] — [3.142]. 

Those based on the pH-dependent redox reaction between the metal and a stable oxide, i.e. antimony, iridium and palladium. 

Delay compositions are mixtures of materials which, when pressed into delay tubes, react without evolution of gaseous products and thus ensure the minimum variation in the delay period. Examples of such mixtures are potassium permanganate with antimony lead dioxide or minium with silicium redox reactions with fluorides and other halides (- also Coruscatives and -+ delay gasless). 

Chloromethyl)tetrafluorophosphorane has been obtained thus far only by the above reaction. It may be noted that, although a redox reaction takes place between (chloro-methyl)dichlorophosphine and antimony (III) fluoride, (chloromethyl)difluorophosphine is the only product formed. The reaction of dichlorophosphines with anti-mony(V) fluoride was the first method of preparation of tetrafluorophosphoranes to be reported. The strongly oxidizing antimony(V) fluoride, however, seems to be required only in special instances, such as the one described below. 

Very recently it has been found that the tertiary butyl derivative ( -Bu)PF2 (b.p. 54°C) can be isolated from the chlorophosphine using antimony trifiuoride as fiuorinating agent (103), suggesting that steric effects may be important in the redox reactions. 

Several synthetic approaches to this class of compounds have been developed, the most convenient being fluorination of the corresponding dialkylaminochlorophosphine with either antimony trifluoride 2S7, 13, 138), zinc fluoride 138, 252), or sodium fluoride in tetramethylene sulfone 287, 291, 270, 213). No redox reactions of the type discussed in Section III are observed. 

On the other hand, fluorination of alkyl- and aryldialkylaminochloro-phosphines, RPC1(NR2), with antimony (or arsenic) trifluoride under similar conditions to reaction (2) affords only the pentavalent fluoro-phosphorane RPFg(NR2) 288, 290) via the same type of redox reaction discussed previously in Section III,A for alkyl- and arylhalophosphines. 

Keggin-type phosphomolybdates (POM s) were tested as catalysts for the selective oxidation of isobutane to methacrylic acid. Doping the POM with antimony improves the catalytic performance especially at isobutane-lean conditions, since a redox reaction between Sb " " and Mo leads to the development of a reduced POM which is stable even in an oxidizing environment, and which is more selective to methacrylic acid. Another important factor to control the reactivity is the pH of precipitation of the POM. When the preparation of the catalyst is carried out via the formation of a lacunary precursor, the time necessary to reach steady catalytic performance ( equilibration time ) is considerably less than that for POM s prepared conventionally at strongly acid pH. An hypothesis about the nature of the active sites is formulated. 

In a previous work we found that the addition of small amounts of Sb3+ to the POM-based catalyst makes possible the occurrance of a redox reaction between Mo in the primary POM structure and antimony, with development of a reduced compound which is stable even under oxidizing conditions [19], The objective of the work reported here was twofold 1) to evaluate the catalytic performance of this Sb-doped POM catalyst in the title reaction, and 2) to analyze the effect of the pH of precipitation of the POM on its chemical-physical features and catalytic performance, as a possible parameter to control the reactivity of these compounds. 

Oxides Compared to silica-based networks, nonsiliceous ordered meso-poious materials have attracted less attention, due to the relative difficulty of applying the same synthesis principles to non-sihcate species and their lower stability (227). Nonsiliceous framework compositions are more susceptible to redox reactions, hydrolysis, or phase transformations to the thermodynamically preferred denser crystalline phases. Template removal has been a major issue and calcination often resulted in the collapse of the mesostracture. This was the case for mesostractured surfactant composites of mngsten oxide, molybdenum oxide, and antimony oxide, and meso-structured materials based on vanadia that were obtained at early stages. Because of their poor thermal stability, none of these mesostructures were obtained as template-free mesoporous solids (85, 228, 229). 

When metallic antimony is fumed with an excess of ammonium chloride, the latter acts like anhydrous hydrogen chloride at elevated temperatures. The result is the formation and sublimation of the volatile antimony chloride which can be detected by the redox reaction with alkaline mercury cyanide solution as described on page 105. 

The free iodine can be detected by the starch test. When applying the redox reaction with iodide, it should be remembered that antimony-bearing organic compounds leave antimony pentoxide or calcium antimonate after ignition with lime and these compounds also set iodine free. The same is true when the ignition residue contains ferric oxide. 

As outlined on page 105, antimony i can be detected by the redox reaction... 

Another route to compounds 33 and 74 was reported (Equation 44) <1999TL3815>. The reaction of [Li(TMEDA)2][l,4,2-P2SbC2But2] 307 with E(S2CNEt2)2 (E = Se or Te) leads to 1,2,4-selenadiphosphole 33 and 1,2,4-telluradiphosphole 74 in 60% and 32% yields, respectively. In both reactions, elemental antimony was deposited from the reaction mixture, which suggests that a redox process is occurring. However, the detailed mechanism is not yet clear. 

Phenyltetrafluorophosphorane was first obtained by the reaction of phenyldichlorophosphine with antimony(V) fluoride or a mixture of antimony(V) chloride and antimony-(III) fluoride. In another method of preparation, phenyl-tetrachlorophosphorane was fluorinated with antimony(III) fluoride. Sulfur(IV) fluoride was used to fluorinate both phenylphosphonic acid and phenylphosphonic difluoride under autogenous pressure. Finally, it was found that phenyltetrafluorophosphorane is formed upon reaction of phenyldichlorophosphine with antimony(III) fluoride, by a simultaneous redox and fluorination reaction. " The last reaction is described below. It is very general in scope and has been employed in the synthesis of a wide variety of tetrafluorophosphoranes. " It may be noted that arsenic-(III) fluoride can be employed similarly as the fluorinating agent instead of antimony(III) fluoride. ... 

The arsenic and antimony pentahalides EX5 (E group 15 element As or Sb X = F or Cl) are strong, irreversible oxidants the gas AsFs has little been used, but SbCF and SbFs are commercially available, very air-sensitive liquids which are used in dry and deoxygenated dichloromethane and liquid sulfur dioxide respectively. SbCls is easier to handle than SbFs which gives the dangerous HF by reaction with moist air. Moreover, SbCls is conveniently used in dichloromethane whereas SbFs is best used in liquid SO2. On the other hand, the side products (halogenation) are more frequently encountered with SbCls than with SbFs. The redox process follows ... 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

In this work, the effect of antimony or vanadium substitutions by titanium over the redox properties and the catalytic behaviour of the solid are studied. In addition, the effect of the antimony content over the deactivation of the catalysts is studied. Kinetic studies at different space-times, and deactivation-reactivation experiments were carried out in order to understand the reaction mechanism. 

Antimony Electrode. The antimony electrode is perhaps the best representative of a whole class of metal/metal-oxide redox electrodes that respond to pH. The potential is probably developed as a result of an oxidation-reduction reaction involving antimony and a skin of antimony(III) oxide which forms on the surface of the metal ... 

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