Metal-ammonia solutions solubility

Aromatic acids are reduced by metal-ammonia solutions very much more readily than simple hydrocarbons and ethers. In contrast to the normal requirements for the latter derivatives, it is often possible to achieve reduction with close to stoichiometric quantities of metal. The addition of aromatic carboxylic acids to liquid ammonia (or vice versa) results in the immediate precipitation of the ammonium salt. As the metal is added, however, the precipitate usually dissolves as reduction proceeds, especially if lithium is used. If reduction is carried out in carefully dried, redistilled ammonia, as little as 2.2 mol of lithium are consumed in some cAses, thereby demonstrating that the substrate is reduced much more readily than the ammonium ions, which instead react with the intermediates from reduction of the substrate. However, protonation by NH4 is not essential since reduction proceeds equally well on preformed metal car-boxylates (although low solubility is then often a problem). The addition of an alcohol is not necessary, but it may serve as a useful buffer and can often improve solubility. The presence of alcohol can nevertheless be deleterious, since it facilitates isomerization of the initially formed 1,4-dihydro isomer to the 3,4-isomer and in this way affords the possibility of further reduction. ... 

Titanium is almost invariably resistant towards neutral salts, particularly halides, at temperatures up to 100°C, and in respect of the latter environments it is significantly more resistant than stainless steel. In strong solutions of caustic alkalis, on the other hand, titanium tends to form soluble titanates, and it is not as resistant as say, nickel. While at low or moderate concentrations of alkali there is no significant attack, the metal has appreciable solubility in concentrated or molten caustic alkali. Titanium is however resistant to attack by aqueous ammonia at all concentrations and temperatures and to anhydrous ammonia . 

Dithizone is a violet-black solid which is insoluble in water, soluble in dilute ammonia solution, and also soluble in chloroform and in carbon tetrachloride to yield green solutions. It is an excellent reagent for the determination of small (microgram) quantities of many metals, and can be made selective for certain metals by resorting to one or more of the following devices. 

In contrast, these metals dissolve and undergo reaction only very slowly in liquid ammonia. Solutions containing alkali metals in liquid ammonia have been known for more than 140 years, and they have properties that are extraordinary. The extent to which the metals dissolve is itself interesting. The solubilities are shown in Table 10.3. 

Silvery-white lustrous metal face-centered cubic crystal structure ductile ferromagnetic density 8.908 g/cm at 20°C hardness 3.8 Mohs melts at 1,455°C vaporizes at 2,730°C electrical resistivity 6.97 microhm-cm at 20°C total emissivity 0.045, 0.060 and 0.190 erg/s.cm2 at 25, 100 and 1,000°C, respectively modulus of elasticity (tension) 206.0x10 MPa, modulus of elasticity (shear) 73.6x10 MPa Poisson s ratio 0.30 thermal neutron cross section (for neutron velocity of 2,200 m/s) absorption 4.5 barns, reaction cross section 17.5 barns insoluble in water dissolves in dilute nitric acid shghtly soluble in dilute HCl and H2SO4 insoluble in ammonia solution. Thermochemical Properties... 

Ohve green hexagonal crystals density 6.05 g/cm decomposes to platinum metal and chlorine on heating at 581°C insoluble in water and alcohol soluble in hydrochloric acid and ammonia solution. 

White crystalline powder sharp metallic taste orthorhombic structure refractive index 1.5452 density 4.20 g/cm very hygroscopic melts at 394°C vaporizes at 650°C highly soluble in water 447g/100 mL at 20°C aqueous solution acidic very soluble in alcohol, ether, and acetone soluble in alkali hydroxides and ammonia solution. 

The synthesis of sodium amide, NaNH2 (or sodamide ), by passing ammonia over heated sodium metal, was first reported almost two centuries ago. A number of studies have since been made of its properties, but no crystal structure has been reported. Sodamide is used as a strong base in organic chemistry (often in liquid ammonia solution). In contrast, sodium bis(trimethylsilyl)amide NaN(SiMe3)2 (or sodium hex-amethyldisilazide , NaHMDS), whose crystal structure is discussed later, is widely used for deprotonation reactions or base catalysed reactions due to its solubility in a wide range of non-polar solvents. An overview of some of the types of chemical reactions in which NaHMDS is used is presented in Scheme 2.3. 

A base is a substance which neutralises an acid, producing a salt and water as the only products. If the base is soluble the term alkali can be used, but there are several bases which are insoluble. It is also a substance which accepts a hydrogen ion (see p. 119). In general, most metal oxides and hydroxides (as well as ammonia solution) are bases. Some examples of soluble and insoluble bases are shown in Table 8.4. Salts can be formed by this method only if the base is soluble. 

However, liquid ammonia will dissolve these metals without reaction to produce solutions having many unusual properties. As shown in Table 5.6, Group IA metals are quite soluble in liquid ammonia. 

One of the interesting characteristics of the metals in Groups IA and IIA is their solubility in liquid ammonia with the Group IA metals being more soluble than those of Group IIA. Some of the chemical and physical aspects of these solutions have been discussed in Chapter 5. 

Silver nitrate solution white, curdy precipitate of silver tartrate, Ag2. C4H4Oe, from neutral solutions of tartrates, soluble in excess of the tartrate solution, in dilute ammonia solution and in dilute nitric acid. On warming the ammoniacal solution, metallic silver is precipitated this can be deposited in the form of a mirror under suitable conditions. 

Dimethylglyoxime reagent yellow, crystalline precipitate of palladium dimethylglyoxime, Pd(C4H702N2)2, insoluble in m hydrochloric acid (difference from nickel and from other platinum metals) but soluble in dilute ammonia solution and in potassium cyanide solution (cf. Nickel, Section III.27, reaction 8). 

Calcium and the other metals are soft and silvery, resembling sodium in their chemical reactivities, although somewhat less reactive. These metals are also soluble, though less readily and to a lesser extent than sodium, in liquid ammonia, giving blue solutions similar to those of the Group 1 metals. These blue solutions are also susceptible to decomposition (with the formation of the amides) and have other chemical reactions similar to those of the Group 1 metal solutions. They differ, however, in that moderately stable metal ammines such as Ca(NH3) + can be isolated on removal of solvent at the boiling point. 

The selenides and tellurides are similar to the sulfides, being preparable from ammonia solutions of the alkali metals. They are water-soluble yet partially hydrolyzed like the sulfides, but are more susceptible to oxidation back to the element. Not every member of the class M cSe3,/Te3, has been fully investigated, but the many that have promise few surprises see Selenium Inorganic Chemistry and Tellurium Inorganic Chemistry). The polonides are similar, and also have their own article see Polonium Inorganic Chemistry). 

The Group 1A metals are extremely soluble in liquid ammonia, releasing hydrogen gas on dissolution. As the metal begins to dissolve, a deep blue solution forms. The color is attributed to the presence of solvated electrons, or e(NH3)r". The metal amide (MNH2) can be isolated by allowing the ammonia to evaporate. 

Since ammonia forms stable, water-soluble complexes with many metals, leaching can be carried out under alkaline conditions to give these metals in solution. Of particular interest are the metals copper, nickel and cobalt, which form particularly stable amines lliat have been well characterized as having the following approximate stability constants (at high ionic strength) Cu, 2 = Cu , 4 = 13 Ni , 6 = 9 = 5 Fe ,j52 < 2. 

If a wet method for collection is selected, such as a wet electrostatic precipitator, fiber-type self-draining mist eliminator, or wet scrubber, ammonia can be regenerated from the salt solution by reaction with a readily available metal oxide such as lime or zinc oxide with formation of a stable sulfur product for disposal. These metal oxides, however, as well as their reaction products, are insoluble and could cause deposition on heat transfer surfaces and/or clogging in the regenerating equipment. Therefore, as indicated in Figure 2, to ensure continuity and reliability of the process, a soluble metal oxide was utilized (in the form of sodium hydroxide solution) to regenerate the ammonia in the experimental work described. This procedure also allows more eflFective utilization of the metal oxide the soluble oxide (NaOH) can be regenerated in batch equipment outside the continuous portion of the process by reaction with either the aforestated insoluble reactants, lime, or zinc oxide. Better control is aflForded in a batch reactor with more eflBcient use of reactants. However, in full-scale equipment undersirable deposition of reactant and product may be controllable so that batch operation may not be necessary. 

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