Iron selectivity

Bi-layer angular movement during current flow, 348, 349, 350 Biological processes, mimicked, 425 Bipolaronic bands as a function of oxidation depth, 342 Bipolar iron-selective film, 226 Bismuth... 

The third step is a Horne r-Wodsworth-Dnnu>ns reaction in which a C-C double bond is created by condensation of ketone 44 with the lithium salt of the p-thia/olephosphoric acid dialkyl ester 12. The desired compound 13 is obtained selectively with Irons geometry The precise mechanism of the Ho me r-Wuds orth Emmons reaction is not yet known, so the source of the irons selectivity remains uncertain. It is assumed that analogous to the Wit tig reaction. an oxaphosphetane forms as an intermediate (see also Chapter 91... 

The irons selectivity in the Honier-Wniisworth-Fmnums reaction can he reversed by structural variation in the phosphonic ester moiety, the so called StilPGetmari variant. In this case tritluoro-substi-tuted ethoxy residues are introduced in the form of phosphonic ester 41, providing access to r/5 substituted acrylic esters. 

Murphy, T.P., Lean, D.R. and Nalewajko, C., 1976. Blue-green algae their excretion of iron-selective chelators allows them to dominate other algae. Science, 192 900-902. 

H H distances coupled with shorter M H distances. However, one has to account for differences in metallic radii, and so in column (iv) the adjusted M-H distances are hsted in which the differences in atomic radii are used as correction factors , with the atomic radius of iron selected arbitrarily as a standard . One can see that colunm (iv) is somewhat smoother than column (iii). Finally, recognizing that one should perhaps consider metal-ligand distances instead of metal-hydrogen distances, two extra columns have been included in which M-X distances are tabulated, where X is the midpoint of the H-H bond. Once again, the unadjusted and adjusted values [columns (v) and (vi) respectively] are listed, in which column (vi) contains the values corrected for differences in atomic radii. 

An iron-selective electrode based on a glass Fe-1173 (Ge2sSbx2Seeo) has been reported to respond to xmcomplexed iron(ni) in sulfate solutions. It was used to evaluate formation constants of iron(III)-sulfate complexes and as an indicator for titrations of sulfate with barium. The mechanism of the sensing action is obscure. 

Murphy, T. P., D. R. S. Lean, and C. Nalewajko (1976), Blue-Green Algae Their Excretion of Iron-Selective Chelators Enables Them to Dominate Other Algae, Science 192, 900-902. 

The importance of the chlorine atoms attached to the radical site in this cyclization is demonstrated by the reversal in stereoselectivity if one chlorine atom is replaced by hydrogen. The variety of cis and Irons selectivity observed suggests that the cyclization proceeds via transition states in which the stcric repulsion between the phenyl substituent and the chlorine atom are of significance. 

The ylid is stabilised by CN as well as by aryl so the phosphonate ester (18) is used instead and the reaction is strongly irons selective. 

Sole, K. C., Viljoen, K., Ferreira, B., Soderstrom, M., Tinkler, O. and Hoffman, L. 2007a. Customising copper-iron selectivity in modified aldoxime extractants pilot plant evaluation. In Proceedings copper 2007, vol. IV, book 2, 3-14. Montreal Canadian Institute of Mining, Metallurgy and Petroleum. 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

In MeOH, l,4-dimethoxy-2-cyclohexene (379) is obtainejl from 1,3-cydo-hexadiene[315]. Acetoxylation and the intramolecular alkoxylation took place in the synthesis of the naturally occurring tetrahydrofuran derivative 380 and is another example of the selective introduction of different nucleo-philes[316]. In intramolecular 1,4-oxyacetoxylation to form the fused tetrahy-drofurans and tetrahydropyrans 381, cis addition takes place in the presence of a catalytic amount of LiCI, whereas the trans product is obtained in its absence[317]. The stereocontrolled oxaspirocyclization proceeds to afford the Irons product 382 in the presence of Li2C03 and the cis product in the presence of LiCl[ 318,319]. 

The original German process used either carbonyl iron or electrolytic iron as hydrogenation catalyst (113). The fixed-bed reactor was maintained at 50—100°C and 20.26 MPa (200 atm) of hydrogen pressure, giving a product containing substantial amounts of both butynediol and butanediol. Newer, more selective processes use more active catalysts at lower pressures. In particular, supported palladium, alone (49) or with promoters (114,115), has been found useful. 

Although acrylonitrile manufacture from propylene and ammonia was first patented in 1949 (30), it was not until 1959, when Sohio developed a catalyst capable of producing acrylonitrile with high selectivity, that commercial manufacture from propylene became economically viable (1). Production improvements over the past 30 years have stemmed largely from development of several generations of increasingly more efficient catalysts. These catalysts are multicomponent mixed metal oxides mostly based on bismuth—molybdenum oxide. Other types of catalysts that have been used commercially are based on iron—antimony oxide, uranium—antimony oxide, and tellurium-molybdenum oxide. 

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice. 

Depressants are reagents that selectively prevent the reaction between a coUector and a mineral, thus preventing its flotation. For example, sodium cyanide [143-33-9] depresses sphalerite [12169-28-7] (zinc sulfide) and pyrite [1309-36-0] (iron sulfide) but not galena. It thus enhances selective flotation of the galena. 

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