Miscellaneous Iron Oxides

A number of other oxides containing iron mixed-valence states are known attention is drawn to some of these. 

Whereas the larger rare-earth ions form the perovskites LnFeOs, the smaller ions (Ln = Ho-Lu, Y) stabilize a series of structures Lni+ Fe2+n04+3 containing the Ln ion in an octahedral site and the iron in trigonal bipyramidal sites. The end member, LnFe204, contains rare-earth basal planes alternating with a double-layer of edge-shared iron sites, see Fig. The other members of the series incorporate intergrowths of a similar 

Phase diagrams and magnetic properties have also been investigated. Magnetic coupling between the iron double layers is weak, but within the layers it is strong. 

MSssbauer data indicate slow electron hopping below room temperature with some evidence for an ordering of Fe and Fe ions below 220 K in YFe204, but fast hopping (th 10 s) at higher temperatures. 

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The polythionate, iron oxide, and iron-cyanide processes are primarily of historical interest and only an abridged discussion of the technology is given. Thioarsenate processes are covered in somewhat greater detail because of the relative importance of these processes in the past. Special attention is given to the quinone and/or vanadium and the iron-chelate processes because they include contemporary processes of major commercial significance. Finally, the sulfur dioxide and miscellaneous processes, which are of les.ser importance, are included for their technical interest. 

MISCELLANEOUS. Sodium hydride, particularly as the dispersion, is effective for removing the last traces of water, alcohols, oxygen, and some sulfur compounds from solvents and certain gases. It reacts with ammonia to form sodium amide, with carbon oxides to form products including formate and oxalate, and with sulfur dioxide to form sodium hydrosulflte. Smalley (52) has tried it for the desulfurization of iron and steel. Its advantage over sodium metal for these reactions is that it holds its fine particle size and reactive surface up to 400 °C., while sodium melts and coalesces at 100°C. unless continually redispersed. 

Those substances which exhibit ferromagnetism are limited to the metals iron, cobalt, and nickel, to certain oxides and carbides containing these elements, and to a small number of miscellaneous substances con-... 

Miscellaneous Reactions. In addition to the key reactions above, DDQ has been used for the oxidative removal of chromium, iron, and manganese from their complexes with arenes and for the oxidative formation of imidazoles and thiadia-zoles from acyclic precursors. Catal)ftic amounts of DDQ also offer a mild method for the oxidative regeneration of carbonyl compounds from acetals, which contrasts with their formation from diazo compounds on treatment with DDQ and methanol in nonpolar solvents. DDQ also provides effective catalysis for the tetrahydropyranylation of alcohols. Furthermore, the oxidation of chiral esters or amides of arylacetic acid by DDQ in acetic acid provides a mild procedure for the synthesis of chiral a-acetoxy derivatives, although the diastereoselectivity achieved so far is only 65-67%. ... 

The amount of iron that needs to be added depends on the waste s initial concentration in miscellaneous colloidal metallic oxides. The concentration is often sufficient (many conosion products in raw FCC condensates) and any excess dosage should be avoided. 

Tartrates give soluble, more or less stable, complexes with miscellaneous cations such as copper, bismuth, and iron, with some metallic hydroxides, acids (such as boric acid), and antimony oxide. The cations become masked by complexation. The identity reaction is carried out, according to the European pharmacopeia, with Fenton s reagent (ferrous sulfate and perhydrol). In a first step, dihydroxyftimaric acid is formed ... 

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