Ammonia thermodynamic stability

A study of the lithium-ammonia reduction of 14-en-16-ones would extend our understanding of the configuration favored at C-14 in metal-ammonia reductions. Although several simple 14-en-16-ones are known, their reduction by lithium and ammonia apparently has not been described in the literature. Lithium-ammonia reduction of A-nortestosterone, a compound that structurally is somewhat analogous to a 14-en-16-one, affords roughly equal amounts of the 5a- and 5 -dihydro-A-nortestosterones. " This finding was interpreted as indicating that there is little difference in thermodynamic stability between the two stereoisomeric products. 

The Dimroth rearrangement of mono- and diamino-l//-l,2,3-triazolo [4,5-c]pyridines 13 to mono- and diamino-3//-l,2,3-triazolo[4,5-h]pyridines 16 took place in ethanolic ammonia and involves diazo-type intermediates 14 and 15 (72JOC3601 73JOC1095). The thermodynamic stability of 16 is greater than that of 13 in the presence of ammonia since treatment of 16 with ethanolic ammonia gave no rearrangement (Scheme 5). 

The structures, thermodynamic stabilities, and mode of decomposition of several simple polyhalides and interhalogens have been extensively studied.However, the chemical reactions of the polyhalides have not been extensively explored. Cremer and Duncan have studied the reactions in the solid phase of dibromoiodide with ammonia. They concluded that the reaction product depended upon the decomposition pressure of the polyhalide. If the decomposition pressure of the IBrJ salt were less than 0.005 mm, the ammonia and the polyhalide would form an addition product, RIBr2 NH3, where R represents the cation. However, if the decomposition pressure of the polyhalide were greater than 0.005 mm, the reaction product would be nitrogen triiodide. To account for this, Cremer and Duncan postulated that at the lower pressures, the polyhalide reacts directly with ammonia whereas, at the higher decomposition pressures, the reaction of the ammonia occurs with the decomposition products. The reaction pathway proposed for the reaction of ammonia with the polyhalide at the higher decomposition pressures is ... 

However, the formation of complexes with low thermodynamic stability fails to qualify such a test. This is due to an appreciable concentration of free metal ions in the solution. The complexes between ammonia and Ca Zn or Al give all the usual precipitation reactions of the free metal ion. 

Already reported CAV/0 microemulsion technique was used to prepare the MLPs [12-15]. Briefly, this technique consists of an oil phase, a colloidal water phase, and surfactants and possesses specific physicochemical properties such as transparency, isotropy, and thermodynamic stability, n-Heptane was used as the oil phase, BrijSO as surfactant and tetraethoxysilane (TEOS) as silica precursor. This method is based on the hydrolysis and the condensation of TEOS. There is a major importance to the concentration and the order of addition of the different species. To the mixture of heptane/BrijSO we add slowly a colloidal suspension of y-Fe203 MPS in water (13 mg in 750 pL of water). After 15 min of stirring we added the cluster units in a mixture of Et0H H20 (1 1). Afterward we introduce an aqueous ammonia solution (28%). Finally the TEOS was added and the microemulsion was stirred during 3 days before several precipitation/resuspension to transfer our MLPs in water. 

Copper Hydroxide. Copper(II) hydroxide [20427-59-2] Cu(OH)2, produced by reaction of a copper salt solution and sodium hydroxide, is a blue, gelatinous, voluminous precipitate of limited stabiUty. The thermodynamically unstable copper hydroxide can be kiaetically stabilized by a suitable production method. Usually ammonia or phosphates ate iacorporated iato the hydroxide to produce a color-stable product. The ammonia processed copper hydroxide (16—19) is almost stoichiometric and copper content as high as 64% is not uncommon. The phosphate produced material (20,21) is lower ia copper (57—59%) and has a finer particle size and higher surface area than the ammonia processed hydroxide. Other methods of production generally rely on the formation of an iasoluble copper precursor prior to the formation of the hydroxide (22—26). 

The and spectroscopy of a solution of 2-chloro-3,5-dinitropyridine in liquid ammonia at-40°C showed the formation of the C-6 adduct (10). This adduct is rather stable, since after 1 hr standing, no change in the spectrum was observed. It is interesting that at a somewhat lower temperature (-60°C) the addition takes place at C-4, i.e., formation of (9). Apparently one deals with the interesting concept of kinetically and thermodynamically controlled covalent adduct formation. At -60°C the addition is kinetically controlled, and at -40°C the addition is thermodynamically favored. The higher stability of the C-6 adduct compared to the C-4 adduct is probably due to the more extended conjugate resonance system (Scheme II.9). 

The participation of Cd(OH)2 in the deposition of CdS (and other metal chalcogenides) has been demonstrated or suggested on many occasions. Kitaev et al. presented a theoretical thermodynamic treatment of the Cd " /ammonia/ thiourea system to show when Cd(OH)2 should be present as a solid phase in the deposition solution [36]. A graphical representation of this analysis is shown in Eigure 3.1. This graph is based on two equilibria the solubility product of Cd(OH)2 and the stability constant of the ammonia (ammine) complex of Cd. Consider first the former ... 

Fig. 3.1 Regions of stability for the Cd-ammonia system for 0.1 M total Cd concentration and at room temperature. The hydroxide line separates conditions where Cd(OH)2 will (above the line) or will not (below the line) thermodynamically exist. The complex line gives the concentration of free Cd + at any pH valne (where the pH is determined only by the ammonia concentration and not, e.g., by added alkali). (Adapted from Ref. 34.)...

Reference 85 presents the thermodynamic side of the previous paper. It is pointed out that although both ammonia and thiourea are present in the solution, because of the much higher stability constant of the Ag-thiourea complexes compared to the Ag-ammines, essentially all the Ag will be present as a thiourea complex. In this case, it can be assumed that the role of ammonia is only to control pH. 

It may readily be seen that the mercurous ion (whether free or in Hg ) is thermodynamically unstable with respect to disproportionation in ammonia, in contrast to its stability in water... 

Classical methods of group analysis and separation take advantage of the stability of the [Ag(NH3)2]+ ion to separate silver from mercury. Treatment of a precipitate containing AgCl with dilute ammonia leads to the reaction in equation (3) bringing the silver into solution. To confirm the presence of Ag+, nitric acid must then be added to cause reprecipitation of AgQ. In aqueous ammonia, the diammine was the highest species formed, and thermodynamic data for its formation are collected in Table 3.20-23... 

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