Hydrogen salt hydrates

For a decade or so [CoH(CN)5] was another acclaimed catalyst for the selective hydrogenation of dienes to monoenes [2] and due to the exclusive solubility of this cobalt complex in water the studies were made either in biphasic systems or in homogeneous aqueous solutions using water soluble substrates, such as salts of sorbic add (2,4-hexadienoic acid). In the late nineteen-sixties olefin-metal and alkyl-metal complexes were observed in hydrogenation and hydration reactions of olefins and acetylenes with simple Rii(III)- and Ru(II)-chloride salts in aqueous hydrochloric acid [3,4]. No significance, however, was attributed to the water-solubility of these catalysts, and a new impetus had to come to trigger research specifically into water soluble organometallic catalysts. 

Although the topology of the hydrogen-bonded water host structure is closely related in the gas hydrates, the alkylamine hydrates, and the alkylammonium salt hydrates, with the pentagonal dodecahedron shown in Fig. 21.3 playing a prominent role, the interactions between the host and guest spedes are different. 

Hydrates with related clathrate-like structures are formed by tetramethyl and tetraethyl ammonium salts. The tetramethyl and tetraethyl ammonium salts form hydrates in which the cations occupy voids in hydrogen-bonded structures formed by the anions and the water molecules. Unlike the gas hydrates, the alkylamine hydrates, and the butyl and isoamyl ammonium salt hydrates discussed in the next section, these cage-like structures do not feature the pentagonal dodecahedron as a common structural component. 

In contrast to the ices, the clathrate hydrates and layer structures described in the preceding chapter, where four-coordinated water is the majority species present in the structure, the water molecules in low hydrates may be three- or four-coordinated. While the water molecule rarely fails to donate two hydrogen bonds, it may accept one or two, but rarely none. This applies both to the organic hydrates discussed in this chapter and the inorganic salt hydrates where the water oxygen can be coordinated to one or two cations (cf. Thble 7.8). 

The eqnUibrium (32) lies to the left side, a 0.1 mol L solntion of ammonia in water is less than 1% dissociated into ions. The undissociated ammonia forms hydrogen-bonded hydrates NH3 XH2O. For comparison, a potassium hydroxide solution is dissociated quantitatively. Ammoninm hydroxide NH4+ OH is only found dissociated in solntion, the undissociated form does not exist. Addition of stronger acids than water, for example, hydrochloric acid, sulfuric acid, or nitric acid, shifts the equilibrimn (32) to the right side, that is, the side of the salts. The reaction of ammonia with hydrochloric acid vapors forms a white nebula in humid air, and white smoke in dry air. 

Quinn R, Appleby JB, Mathias PM, and Pez GP. Liquid salt hydrate acid gas absorbents An unusual desorption of carbon dioxide and hydrogen sulfide upon solidification. Sep. Sci. Technol. 1995 30 1711-1723. 

VI. Hydrogen Bonding Systems in Acid Salt Hydrates.107... 

Khan AA, Banr WH (1972) Salt hydrates. Vtll. The crystal structmes of sodium ammonium orthochromate dihydrate and magnesinm diammoninm bis(hydrogen ortho phosphate) tetrahydrate and a discussion of the ammoninm ion. Acta CrystallogrB28 683-693... 

Electronic Mechanism. According to Luder and Zuffanti, the use of iron and acids to reduce nitrobenzene to aniline can be explained as follows Any acid (using the word in the Lewis sense) will increase the concentration of hydrogen ions (hydrated, of course) in water solution. The salts (FeCh and RNH3CI) and cations that have appeared in the equations above are acids in this general Sense, and in the presence of iron and water a plentiful supply of both electrons and protons is available. 

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