Ammonium ions, decomposition

Heath and Majer (H3) have recently used a mass spectrometer to study the decomposition of ammonium perchlorate. Decomposition was detected in the range from 110° to 120°C. At this temperature, there were ions in the mass spectrum caused by NH3, HC104, Cl2, HC1, nitrogen oxides, and 02. The appearance of the species NO, N02,02, and Cl2 in the decomposition products under very low pressure (i.e., in the absence of gas-phase molecular collisions) indicates that the principal decomposition reactions take place in the crystal and not in the gas phase. 

Quaternary ammonium salts are generally stable under neutral or acidic conditions up to 150°C, but decomposition can occur with the quaternary ammonium ion acting as an alkylating agent in its reaction with anions (Scheme 1.1). Soft nucleophiles, such as RS, are more reactive with tetra-n-butylammonium bromide and benzyltriethylammonium chloride, although the latter salt also C-benzylates phenyl-acetonitrile under basic conditions [46], These side reactions are considerably slower than the main catalysed reactions with, for example, a haloalkane and the amount of unwanted impurity in the final alkylated product is never greater than the amount of catalyst used (i.e. generally > 2%). Harder anions, e.g. R2N and RO, rarely react with the ammonium salts. 

The precise reactions involving the decomposition of ammonium ions and nitrate ions at the anodic surface to form N-doped titania are currently unclear, and the subject of ongoing studies. However, the anodization of aluminum in nitric acid has been studied previously and is known to be relatively complex... 

The effect of temperature on ammonia adsorption by ZSM5 samples has been investigated by microcalorimetry, varying the adsorption temperature from 150 to 400°C [235]. The initial heats of adsorption were independent of temperature up to 300°C. When the adsorption temperature increased, there was a competition between the formation of ammonium ions on Brpnsted sites and their decomposition. The total number of titrated sites decreased with increasing adsorption temperature. It appeared that an adsorption temperature between 150 and 300°C is appropriate for these calorimetric experiments. 

The formation of novel silicon-rich synthetic zeolites has been facilitated by the use of templates, such as large quaternary ammonium cations instead of Na+. For instance, the tetramethylammonium cation, [(CH3)4N], is used in the synthesis of ZK-4. The aluminosilicate framework condenses around this large cation, which can subsequently be removed by chemical or thermal decomposition. ZSM-5 is produced in a similar way using the tetra-.n-propyl ammonium ion. Only a limited number of large cations can fit into the zeolite framework, and this severely reduces the number of [AIO4] tetrahedra that can be present, producing a silicon-rich structure. 

They therefore concluded that several different rate-determining steps were involved in the deposition. Figure 3.6 shows the dependence of the deposition rate on the concentration of the reactants (Cd, thiourea, ammonia, and pH—the last varied through introduction of ammonium ion) (a) as well as an Arrhenius plot of the deposition (b) for the CdS deposition. From the kinetic data, they deduced the hydroxide-complex-decomposition mechanism, given earlier in Eqs. (3.50) and (3.51) and, more specifically, as... 

While deposition rate normally increases with increase in pH for the standard bath, using an ammonium salt to lower the solution pH resulted in the opposite behavior i.e., increased pH led to slower deposition [22]. The pH in these experiments was increased by adding NH4OH. Increased pH (and NH4OH) results in two opposing effects Thiourea decomposition increases but free [Cd ] decreases. Since the deposition rate for the solution with no added NHj increases with increase in pH, the former apparently outweighs the latter. When extra ammonium ion is added, much more ammonium hydroxide is needed to increase the... 

Furthermore, investigations of template decomposition in zeolites upon calcination of the as-synthesized materials have received much attention by researchers (248-250). However, the decomposition mechanisms of quaternary ammonium salts, which are commonly used as templates for zeolite synthesis, are still not well understood. Thus, MAS NMR investigations of the decomposition of quaternary ammonium ions in zeolites bear the potential of significantly improving the understanding of these processes (243,251). For this purpose, a general method was developed for the synthesis of... 

The above-mentioned route to the preparation of quarternary ammonium ions in acidic zeolites is remarkable for the following reasons an immobilization of quaternary ammonium ions in a well-controlled concentration is an approach to modification of zeolite catalysts. Furthermore, the synthesis of isotopically labeled compounds is of importance in organic, pharmaceutical, and agricultural chemistry. This method is an approach to the synthesis of C-labeled (or C, N-labeled) tertiary amines via a thermal decomposition (243,251) of the corresponding quaternary ammonium ions in zeolites. 

A study is presented of the synthesis and properties of the novel synthetic zeolite omega. The synthesis variables and kinetics of formation are discussed, as well as the ion exchange, sorption, and thermal properties. By decomposition of imbibed tetra-methylammonium ions and exhaustive treatments of the zeolite with ammonium ions, a pure hydrogen form can be obtained which is a suitable substrate for the preparation of hydrocarbon conversion catalysts. Several catalysts were prepared and utilized to isomerize n-hexane, and to hydrocrack a heavy gas oil. 

The ammonium ion (NH4+), produced by fermentative bacteria that use nitrite as an oxidant, or produced during the decomposition of organic materials, is an important source of nitrogen for many plants and bacteria. Nevertheless, under vigorous aerobic conditions much of the NH4+ so produced is converted back to nitrite and nitrate by nitrifying bacteria. 

Uytterhoeven et al. (146) proposed that the protons liberated by decomposition of the ammonium ions attacked the oxygen atoms of the zeolite framework to form structural hydroxyl groups. The infrared absorption bands at 3650 and 3550 cm-1 were ascribed to hydroxyl groups of this type. The mechanism of formation of the hydroxyl groups is shown in the following two equations. 

The appearance of the hydroxyl bands at 3650 and 3550 cm-1 upon heating the ammonium form accompanies the decrease and disappearance of the NH-stretching bands as ammonia is evolved. The rate of decomposition of the ammonium ions appears to be influenced by the calcination conditions. Ward observed that most of the ammonium ions decomposed between 200° and 350°C, and at 420° only discreet hydroxyl bands were present (148). With extensively exchanged samples (>90% of the exchange sites occupied by ammonium ions), the 3550-cm I band was more intense than that at 3650 cm-1, in contrast to the intensity relationship observed at lower ammonium-exchange levels. Angell and Schaffer also noted the variability of the relative intensities of the two bands with different extents of ammonium ion exchange. 

Thermal activation of the clay up to 600°C results in a simultaneous loss of ammonia and structural hydroxyl groups. During decomposition, the ammonium ions release protons to the clay framework. Infrared spectra of dehydrated SMM samples exposed to ammonia vapor showed small amounts of ammonium ions and Lewis-bound ammonia. The ammonium ion was thought to result from interaction with silanol groups at crystal edges. Partially dehydrated samples adsorbed larger amounts of ammonia, and a greater proportion was present as ammonium ion, probably because of the lesser extent of dehydroxylation. 

Maleic anhydride decomposes exothermically, evolving carbon dioxide, in the presence of alkali- or alkaline earth- metal or ammonium ions, dimethylamine, triethylamine, pyridine or quinoline, at temperatures above 150°C [1]. Sodium ions and pyridine are particularly effective, even at concentrations below 0.1%, and decomposition is rapid [2]. An industrial incident involved gas-rupture of a large... 

FIGURE 11.27 Decomposition temperature as a function of MMT loading of PS nanocomposites. The MMT is modified with (filled square) dimethyl(hydrogenated tallow alkyl)benzyl ammonium ion, (filled circle) dimethyl di(hydrogenated tallow alkyl) ammonium ion, (filled triangle) dimethyl(hydrogenated tallow alkyl) 2-ethylhexyl ammonium ion, and (open square) NaMMT. (From Doh, J.G. and Cho, I., Polym. Bull., 41, 511, 1998. With permission.)... 

It was found impossible to measure the rate of decomposition by the evolution of gases because the release of these gas bubbles is very slow and erratic. The course of the reaction was followed by analyzing samples for the ammonium ion. Small amounts of the decomposing amalgam were forced through a capillary tube into a chilled solution of an iodate. The ammonium reacted with iodate ion to give iodide ion. The solution was then acidified with acetic acid and the iodine distilled out, collected and titrated with sodium thiosulfate. The method was checked with samples... 

It was found that this heterogeneous reaction can be stopped by the addition of small amounts of lithium. It is likely that lithium with its higher electrode potential is able to prevent the self-ionization of liquid ammonia, and the heterogeneous reaction between ammonium in solution and liquid ammonia is inhibited. When this heterogeneous reaction is prevented, the decomposition follows a perfectly satisfactory second-order reaction, and the temperature must be raised up to the range from zero to 20° in order to obtain a measurable reaction rate. The reaction is satisfactorily explained on the assumption that ammonium dissociates in mercury giving ammonium ions and free electrons NH4—>NH4+ -be . The older view that the ammonium exists as a free radical, NH4, seems less likely. Such a radical would be unstable and it would not be expected to have such a long life. Ammonium ions, however, are more stable. 

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