Antimony, intermediate oxid

Antimony antimoniate—Intermediate oxid—Diantimonie te-troxid—SbjOi—304—occurs in nature, and is formed when the-oxids or hydrates of Sb are strongly heated, or when the lower stages of oxidation or the sulflds are oxidized by H2iO>, or by fusion with sodium nitrate. It is insoluble in HaO but is decomposed by HCl, hydropotassie tartrate, and potash. 

MAA and MMA may also be prepared via the ammoxidation of isobutylene to give meth acrylonitrile as the key intermediate. A mixture of isobutjiene, ammonia, and air are passed over a complex mixed metal oxide catalyst at elevated temperatures to give a 70—80% yield of methacrylonitrile. Suitable catalysts often include mixtures of molybdenum, bismuth, iron, and antimony, in addition to a noble metal (131—133). The meth acrylonitrile formed may then be hydrolyzed to methacrjiamide by treatment with one equivalent of sulfuric acid. The methacrjiamide can be esterified to MMA or hydrolyzed to MAA under conditions similar to those employed in the ACH process. The relatively modest yields obtainable in the ammoxidation reaction and the generation of a considerable acid waste stream combine to make this process economically less desirable than the ACH or C-4 oxidation to methacrolein processes. 

As discussed, there are various methods of cation-radical generation. Every individual case needs its own appropriate method. A set of these methods is continuously being supplemented. For example, it was very difficult to prepare the cation-radicals of benzene derivatives with strong acceptor groups. However, some progress has been achieved, thanks to the use of fluorosulfonic acid, sometimes with addition of antimony pentafluoride, and lead dioxide (Rudenko 1994). As known, superacids stabilize cationic intermediates (including cation-radicals) and activate inorganic oxidants. The method mentioned is effective at -78°C. Meanwhile, -78°C is the boundary low temperature because the solution viscosity increases abruptly. This leads to the anisotropy of a sample and a sharp deterioration in the ESR spectrum quality. 

Other more anecdotic ways of activating [ F]fluoride are its coordination with protonated 1,8-b/s-(dimethylamino)naphthalene, its coordination with antimony oxide or its purification via an intermediate [ F]fluorotrimethylsilane formation. 

In comparison to the bismuth molybdate and cuprous oxide catalyst systems, data on other catalyst systems are much more sparse. However, by the use of similar labeling techniques, the allylic species has been identified as an intermediate in the selective oxidation of propylene over uranium antimonate catalysts (20), tin oxide-antimony oxide catalysts (21), and supported rhodium, ruthenium (22), and gold (23) catalysts. A direct observation of the allylic species has been made on zinc oxide by means of infrared spectroscopy (24-26). In this system, however, only adsorbed acrolein is detected because the temperature cannot be raised sufficiently to cause desorption of acrolein without initiating reactions which yield primarily oxides of carbon and water. 

Sulfides are selectively fluorinated a to the sulfur atom via a reaction similar to the Pummerer rearrangement (Table 2). The fluorination wa.s originally achieved by the direct fluorination of sulfides with xenon difluoride.This reaction is proposed to occur by initial oxidative fluorination of the sulfide to give an unstable sulfur(IV) difluoride of type 1, followed by loss of hydrogen fluoride to give intermediate 2, followed by fluorine transfer to give the a-fluoro sulfide. This fluorination has also been achieved with diethylaminosulfur trifluoride (DAST) in the absence or presence of catalytic amounts of antimony(III) chloride (see Vol. ElOa, pp 421-423). ... 

AH catalysts claimed are multi-functional systems. Indeed, the formation of acrylonitrile from propane occurs mainly via the intermediate formation of propene, which is then transformed to acrylonitrile via the allylic intermediate. It follows that the catalyst possesses different kinds of active site one site that is able to activate the paraffin and oxidehydrogenates it to the olefin, and one site that (amm)oxidizes the adsorbed olefinic intermediate. This second step must be very rapid to limit, as much as possible, the desorption of the olefin. In order to develop an effective cooperation between the two sites, it is necessary to have systems in which they are in close proximity. The muIti-functionaHty is achieved either through the combination of two different compounds (phase-cooperation), or through the presence of different elements inside a single crystaUine structure. In antimonate-based systems, the cooperation between the metal antimonate (having the rutile crystalline structure), responsible for propane oxidative dehydrogenation to propene and propene activation, and antimony oxide, active in allylic ammoxidation, is made more efficient through the dispersion of the latter compound over... 

This demonstration marked the beginnings of the CFC industry as we know it today. Continuous processes were developed wherein a chlorocar-bon and HF were fed to a reactor containing antimony pentahalide, usually dissolved in the fluorinated reaction intermediates. Under reaction conditions, pentavalent antimony is somewhat unstable, reverting back to the trivalent state and chlorine. Industry practice is to feed chlorine to oxidize trivalent antimony back to the pentavalent state. In its simplest form the exchange reaction with CCI4 can be written as shown in Eqs. (4) and (5). Over the years, several improvements to such processes have been made... 

S,A. Veniaminov and G,B, Ikirannik Intermediates in the interaction of 1-butene and butadiene with an iron-antimony oxide catalyst, React, (tinet. Catal, Lett., 13 (4) (1980) 413 418,... 

In view of these observations it would seem sensible that the influence of adjacent superficial antimony and tin ions should also be considered in terms of likely mechanisms. Immediately one would recall the suggestion (72) that the catalytic properties may be related to the blue color of the material, which has been associated with a possible Sb -Sb charge transfer process. Such an association may then be related to the kinetics of butene oxidation, which have been interpreted in terms of the formation of allylic intermediates at active centres containing Sn and Sb ions. Indeed, McAteer (76) has suggested that these active centers have acidic and basic functions and consist of surface oxide ions of different electron density as determined by the coordinated cations. McAteer described the pattern of selectivity for the formation of butadiene and a-ketone according to the depiction in Fig. 7a. The initial step was postulated as the formation at an acid center of a positively charged allyl ion which is ti or a bonded at an adjacent basic site. The formation of butadiene was attributed to proton abstraction from the zr-allyl intermediate, its facile desorption at surfaces... 

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