Crystalline solids hydrates

The utilization of IR spectroscopy is very important in the characterization of pseudopolymorphic systems, especially hydrates. It has been used to study the pseudopolymorphic systems SQ-33600 [36], mefloquine hydrochloride [37], ranitidine HC1 [38], carbovir [39], and paroxetine hydrochloride [40]. In the case of SQ-33600 [36], humidity-dependent changes in the crystal properties of the disodium salt of this new HMG-CoA reductase inhibitor were characterized by a combination of physical analytical techniques. Three crystalline solid hydrates were identified, each having a definite stability over a range of humidity. Diffuse reflectance IR spectra were acquired on SQ-33600 material exposed to different relative humidity (RH) conditions. A sharp absorption band at 3640 cm-1 was indicative of the OH stretching mode associated with either strongly bound or crystalline water (Fig. 5A). The sharpness of the band is evidence of a bound species even at the lowest levels of moisture content. The bound nature of this water contained in low-moisture samples was confirmed by variable-temperature (VT) diffuse reflectance studies. As shown in Fig. 5B, the 3640 cm-1 peak progressively decreased in intensity upon thermal... 

Compound M is much more stable than L. Any attempt to remove water of hydration from L resulted in its rapid polymerization. Stabilisation of crystalline solid hydrated L is probably due to a high interaction energy between zwitterion and water molecules in the crystal lattice. 

This review article is concerned with the structure, bonding, and dynamic processes of water molecules in crystalline solid hydrates. The most important experimental techniques in this field are structural analyses by both X-ray and neutron diffraction as well as infrared and Raman spectroscopic measurements. However, nuclear magnetic resonance, inelastic and quasi elastic neutron scattering, and certain less frequently used techniques, such as nuclear quadrupole resonance, electron paramagnetic resonance, and conductivity and permittivity measurements, are also relevant to solid hydrate research. 

Both X-ray and neutron diffraction methods are applied to determine the structure of crystalline solid hydrates. Because of the very small scattering cross-section of hydrogen atoms for X-rays it is much desirable to solve the crystal structure by means of neutron diffraction techniques. 

The traditional definition of a zeolite refers to microporous, crystalline, hydrated aluminosilicates with a tliree-dimensional framework consisting of comer-linked SiO or AlO tetrahedra, although today the definition is used in a much broader sense, comprising microporous crystalline solids containing a variety of elements as tetrahedral building units. The aluminosilicate-based zeolites are represented by the empirical fonmila... 

KEY TERMS amorphous crystalline diffraction hydrate solid emulsion... 

What form of the solid is present (i.e., particle morphology, polymorphic species, degree of crystallinity, (an)hydrate), and is this form thermodynamically stable over the temperature and relative humidity range that the solid is expected to encounter ... 

It is the objective of this chapter to discuss the various mechanisms whereby water can interact with solid substances, present methodologies that can be used to obtain the necessary data, and then discuss moisture uptake for nonhydrating and hydrating crystalline solids below and above their critical relative humidities, for amorphous solids and for pharmaceutically processed substances. Finally, transfer of moisture from one substance to another will be discussed. 

The sorption of water vapor onto nonhydrating crystalline solids below RHq will depend on the polarity of the surface(s) and will be proportional to surface area. For example, water exhibits little tendency to sorb to nonpolar solids like carbon or polytetrafluorethylene (Teflon) [21], but it sorbs to a greater extent to more polar materials such as alkali halides [34-37] and organic salts like sodium salicylate [37]. Since water is only sorbed to the external surface of these substances, relatively small amounts (i.e., typically less than 1 mg/g) of water are sorbed compared with hydrates and amorphous materials that absorb water into their internal structures. 

Gas hydrates are crystalline compounds in which smaller gas molecules (<0.9 nm) are encaged inside the lattices of hydrogen-bonded ice crystals. The gas molecules in the crystalline solids are effectively compressed, volumetrically, by a factor of 164. A comprehensive review of the physical and chemical properties of gas hydrates can be found in Sloan (1998, 2003). 

Savage, H. 1986. Water structure in crystalline solids Ices to proteins. In Water Science Reviews 2 Crystalline Hydrates (F. Franks, ed.), pp. 67-148. Cambridge Univ. Press, Cambridge, UK. 

One borderline circumstance, which should be considered as intentional chemistry for purposes of managing chemical reactivity hazards, is hydration. For example, anhydrous copper sulfate is a white solid with the formula CuS04. When it is crystallized from water, a blue crystalline solid with the formula CuS04-5H20 results, and the water molecules are an integral part of the crystal (Parker 1997). 

Properties and extraction processes At high pressures and low temperatures, water and gas form an ice-like mixture, called gas hydrate, also known as clathrate or simply hydrate. Hydrates are a crystalline, solid substance composed largely of water... 

Natural gas (methane) can be obtained from gas hydrates. Gas hydrates are also called clathrates or methane hydrates. Gas hydrates are potentially one of the most important energy resources for the future. Methane gas hydrates are increasingly considered a potential energy resource. Methane gas hydrates are crystalline solids formed by combination of methane and water at low temperatures and high pressures. Gas hydrates have an iee-hke crystalline lattiee of water molecules with methane molecules trapped inside. Enormous reserves of hydrates can be foimd imder eontinental shelves and on land under permafrost. The amount of organic... 

In aqueous media lutetium occurs as tripositive Lu3+ ion. All its compounds are in +3 valence state. Aqueous solutions of all its salts are colorless, while in dry form they are white crystalline solids. The soluble salts such as chloride, bromide, iodide, nitrate, sulfate and acetate form hydrates upon crystallization. The oxide, hydroxide, fluoride, carbonate, phosphate, and oxalate of the metal are insoluble in water. The metal dissolves in acids forming the corresponding salts upon evaporation of the solution and crystallization. 

The hydrated salt, ZnF2 4H20, is a white crystalline solid rhombohedral crystals density 2.30 g/cm loses water of crystallization at 100°C sparingly... 

Benzotriazine (8, R = H), for example, can be isolated as a reasonably stable, colorless crystalline solid, but it reacts rapidly in solution with water to give o-aminobenzaldehyde, presumably by initial covalent hydration to give 98, which decomposes to o-aminobenzaldehyde via the triazene 99. Reaction of 8, R = H, with other nucleophiles also occurs readily, while 4-substituted 1,2,3-benzo-triazines react similarly but more slowly, as expected, owing to a combination of steric and electronic effects. 

Investigations on the adsorption of gases, on the rates of catalytic processes (see Rideal and Taylor, Catalysis in Theory and Practice) and on the dissociation of crystalline solids such as hydrates or carbonates have revealed another interesting phenomenon. 

Lanford, W. A., Davis, K., Lamarche, P., Laursen, T., Groleau, R. Doremus, R. H. 1979. Hydration of soda-lime glass. Journal of Non-Crystalline Solids, 33, 249-266. 

All three hydrates have been isolated in the form of white crystalline solids. With more cone. soln. the liquid separates into two layers on cooling. The lighter liquid is almost pure hydrogen chloride with very little dissolved water. Soln. with between 67 and 99 per cent, hydrogen chloride do not exist at low temp. The solubility of water in liquid hydrogen chloride, LK, is less than 0 1 per cent, at 0°, and at the most 0 2 per cent, at 30°. The lower aq. layer, GH, represents soln. of liquid hydrogen chloride in water, which decreases with rise of temp. ... 

Stability of the compounds 86 varies dramatically with the nitrogen substituent. Methyl" and phenyl s derivatives (86 R = Me or Ph) are moderately stable crystalline solids—often hydrated (87 or 88 X = OH). The 2,4-dinitrophenyl derivative [86 R = C6H3(NO2)2, R = H] is less stable but can be isolated as orange prisms (mp 112°C)5° It readily rearranges to the diaryl ether 96 (mp 128°C) with which it was originally confused.5The monomeric 5-nitro-2-pyridyI derivative is similarly unstable and in solution dimerizes giving adduct 97a. 5 5 The 4,6-di-methylpyrimidin-2-yl derivative can only be isolated as the dimers 97b and... 

If an aqueous solution of hydroqumone is cooled while under a pressure of several hundred kilopascals (equals several atmospheres) of a noble gas [X = Ar. Kr. Xe. a crystalline solid of approximate composition [C HjfOHLljX is obtained. These solids are 0-hydroquinone dathrates with noble gas atoms filling most of the cavities.5 Similar noble gas hydrates are known (Fig. 17 l). These clathmlcs are of some importance since they provide a stable, solid source of the noble gases. They have also been used to effect separations of the nohle gases since there is a certain selectivity exhibited by the cfctihnucs. 

Gas hydrates behave as solutions of gases in crystalline solids rather than as chemical compounds. The main framework of the hydrate crystal is formed with water molecules. The hydrocarbon molecules occupy void spaces within the lattice of water molecules. 

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