Dehydration of hydrate

Iron(II) bromide [7789-46-0] FeBr2, can be prepared by reaction of iron and bromine ia a flow system at 200°C and purified by sublimation ia oitrogea or uader vacuum. Other preparative routes iaclude the reactioa of Fe202 with HBr ia a flow system at 200—350°C, reactioa of iroa with HBr ia methanol, and dehydration of hydrated forms. FeBr2 crystallizes ia a layered lattice of the Cdfy type and has a magnetic moment of... 

The dehydration of hydrates has been widely used, both by earlier workers (2) and recently (20). Heating ammoniates ScF3-0.4NH3, YF3 0.35NH3, and LnF3-nNH3 also gives anhydrous trifluorides in a convenient manner (2 2). 

Chemisorption of anions at the electrode interface involves dehydration of hydrated anions followed by adsorption of dehydrated anions which, then, penetrate into the compact double layer to contact the interface directly, this result is called the contact adsorption or specific adsorption. The plane of the contact adsorption of dehydrated anions is occasionally called the inner Helmholtz plane... 

The kinetic treatment for the electron transfer of ligand-coordinated redox particles described in Sec. 8.4.1 may, in principal, apply also to the electron transfer of adsorbed redox particles (inner-sphere electron transfer). The contact adsorption of redox particles on metal electrodes requires the dehydration of hydrated redox particles and hence inevitably shifts the standard Fermi level of redox electrons from in the hydrated state to in the adsorbed state. This shift of the Fermi level of redox electrons due to the contact adsorption of redox particles is expressed in Eqn. 8-83 similarly to Eqn. 8-79 for the complexation of redox particles (ligand coordination) ... 

This explanation is supported by nmr rate data for the dehydration of hydrated pyruvic acid, which is similar to glyoxalate. For this at 25 °C... 

In contrast to the many sulfates (see Chapter 4), there are very few anhydrous sulfites about which much is known. (See Figure 3.1.) They are usually prepared by the dehydration of hydrates and thus may not be entirely water-free. This may affect the decomposition reactions, since in some instances water and S02 evolve simultaneously. 

The rare earth sulfites have potential applications in thermochemical cycles and as starting materials for the preparation of sulfides which can be formed by the reduction of sulfites, e.g., by CO.15,16 One problem is that the anhydrous sulfites apparently cannot be synthesized directly, but only by the dehydration of hydrates. Thus, great care must be taken to avoid decomposing the salt while water is removed, frequently by removal of S02. The decomposition product is frequently an oxysulfate, or sulfite-sulfate, e.g., Ce2(S03)2S04 and Ce2S03(S04)4. Listed are several references which will provide the reader with entry into the field, many by workers at Helsinki University.16 19... 

FIGURE 6 Various possibilities that arise from dehydration of hydrate. A hydrate can dehydrate reversibly into various solid-state forms. It can dehydrate to form an anhydrous form of the drug or to a lower hydrate. Hydrate can also dehydrate to form an isomorphic desolvate where the crystal lattice is retained except for the absence of water. The crystal structure may also collapse on dehydration to form an amorphous form. Hydrates on dehydration can also result in different polymorphs. 

Attempts at identifying the influence of structme on stability have generally been inconclusive. For example, some alkali metal permanganates with comparable stmctures show similarities of decomposition behaviour [29], while, in contrast, the decompositions of several cobalt(lll) ammine azides show little evidence of structural influences [76], Significant differences in behaviour were found for the various crystal forms of the LiK tartrate hydrates [87] and, also, for the dehydrations of the isomorphic alums [20,43], However, some reactants, for example those prepared by the dehydration of hydrated metal carboxylates [5], may be amorphous to X-rays, thus preventing recognition of any control of stability by crystal structure. 

Minami H, Inoue T. Dehydration of hydrated bilayer of dipalmitoylphospha-tidylcholine caused by beryllium ion evidence from a differential scanning calorimetry of bilayer phase transition. J Colloid Interface Sci 1998 206 338-341. 

Anhydrous BeCl2 (mp 688 K, bp 793 K) can be prepared by reaction 11.16. This is a standard method of preparing a metal chloride that cannot be made by dehydration of hydrates obtained from aqueous media. In the case of Be, [Be(H20)4] is formed and attempted dehydration of... 

Dehydration of hydrated halides. Hydrated halides are usually obtained easily from aqueous solutions. They can sometimes be dehydrated by heating them in a vacuum, but often this leads to oxo halides or impure products. Various reagents can be used to effect dehydration. For example, SOCl2 is often useful for chlorides. Another fairly general reagent is 2,2-dimethoxy-... 

H. S. Sherry (Mobil Research Development Corp., Princeton, N. J. 08540) From the chabazite ion exchange kinetics, you deduce that two kinds of sites must be involved and that one of these sites is in the hexagonal prism. I believe that J. V. S. Smith and coworkers of the University of Chicago showed that the site in the hexagonal prism is occupied only after dehydration of hydrated CaA. This site is empty in the hydrated zeolite and thus is not likely to be involved in Sr-Na ion exchange. 

Isobaric dehydration of hydrated oxide by heating even below 90°C at 10 mm. results in a small but definite loss of oxygen this increases above 100°C to the point where the completely dehydrated product, obtained by heating at 330°C has only the composition TI3O3 a- Some elemental T1 also begins to sublime at 330°C. 

I. DEHYDRATION OF HYDRATED BROMIDE-NH4Br MIXTURES IN A STREAM OF HBr... 

Dehydration of hydrated oxides in the mother liquor [see lead (IV oxide, p. 1668]. 

Dehydration of hydrates can also lead to the formation of unique crystals. Caffeine Form II was prepared by recrystallizing caffeine from water, drying for 8 days at 30°C, and then heating for 4 hours at 80°C [38]. Chloroquine diphosphate 3 1 hydrate was converted to the anhydrous form at temperatures above 188°C [49]. Etoposide Form I (a monohydrate) was found to undergo a dehydration reaction in the temperature range of 85-115°C to yield etoposide Form la. This form could be melted at 198°C and transformed to etoposide Form Ila, which itself melted at 198°C and crystallized to still another polymorph, etoposide Form Ila at 206°C. Etoposide Form Ila was found to melt at 269°C and convert to its hydrated form, etoposide Form n, when exposed to the atmosphere at room temperature. This hydrate was also found to undergo a dehydration reaction at 90-120°C to yield etoposide Form Ila [50]. 

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