Decomposition in Organic Solvents

The decomposition of AB material in solution could be attractive for many reasons. From a chemical engineering point of view, the use of a liquid fuel is generally preferred because of the simplifled transport compared to solid materials. Liquid AB hydrogen sources can be used to improve the controllability of the AB decomposition by separating the decomposition zone (reactor) from the storage tank. This measure would be an important improvement with respect to safety, since the dehydrogenation reaction potentially bears the risk of a thermal run-away due to its exothermic nature. 

From a chemical point of view, the AB decomposition in solution may allow one to adjust the type of decomposition product obtained after dehydrogenation and thus may influence the recycling strategy to be applied. Furthermore, benefits from improved kinetics can also be expected. Of course, the fundamental prerequisite is a high solubility and the stability of ammonia borane in the solvent in question. Corresponding data are given in Section 8.2. 

For example, in diglyme and monoglyme AB is not entirely decomposed at 85 °C even after 9 and 25 h, respectively. Dixon and coworkers [86] reported that AB in monoglyme (0.14 M) releases only 0.05equiv H2 at 60 °C after 24h. As expected, the H2 release can be fast at higher temperatures, the complete conversion of AB into borazine (BHNH)3 requires less than 3h at 130-140°C [85]. Wideman and Sneddon [87] used the thermal decomposition of AB in solution for the laboratory scale preparation of borazine. For this purpose, solid AB was added slowly, over the course of 3 h, to tetraglyme at 140-160 °C. Borazine was removed from the reaction mixture, trapped at —78 °C, and isolated, resulting in a 67% yield. 

Two factors concerning the solubility of the Rh-clusters need to be taken into account  

Baker and coworkers [98] investigated catalysts based on complexes of Ni, Ru, and Rh with strong electron-donating ligands, such as N-heterocyclic carbenes (NHGs). 

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Decomposition of the double salts to ArHgX is achieved in organic media, e.g., in McjCO or EtOAc, or equally well in HjO. The solid double salt is added in small portions to a stirred suspension of Cu powder in the solvent (ca. 30-50 mL of solvent per 10 g double salt) at ca. 0°C for decompositions in HjO and —50° to — 20°C in McjCO solutions. Complete consumption of the diazonium salt can be tested for using 2-naphthol. In decompositions in H2O, the organomercurials separate, whereas in decompositions in organic solvents evaporation of the solvent and extraction of the residue by a solvent is used to obtain ArHgX. 

Fig. 7.27. XRD pattern, TEM image (insert) of the CdS nanowires prepared by precursor decomposition in organic solvent.

Blue-black, extremely hygroscopic crystals dark green if oxychloride is present. M.p. 194°, b.p. 268° d 2.927s. Soluble in water and alcohol (solvolysis) soluble without decomposition in organic solvents such as ether, CHCI3, CCI4 and CSg. 

Beryllium Hydride. BeryUium hydride [13597-97-2] is an amorphous, colorless, highly toxic polymeric soHd (H = 18.3%) that is stable to water but hydroly2ed by acid (8). It is insoluble in organic solvents but reacts with tertiary amines at 160°C to form stable adducts, eg, (R3N-BeH2 )2 (9). It is prepared by continuous thermal decomposition of a di-/-butylberylhum-ethyl ether complex in a boiling hydrocarbon (10). 

The amorphous alkaloids include a substance, giving fluorescent solutions in organic solvents, which is thought to be a decomposition product of ibogaine. 

The temperature of the stirred solution is readjusted to 15°, and stirring at this temperature is continued until the precipitate reverts to a deep red macrocrystalline form. Petroleum ether (200 ml) is then added to the reaction mixture, the precipitate is allowed to settle, and the solvent mixture is decanted. The residue is washed three times with 200-ml portions of 30-60° petroleum ether, the solvent being removed each time by decantation. The precipitate is collected by suction filtration, dried at room temperature under a vacuum of 10 mm (higher vacuum causes some surface decomposition), and stored in a desiccator. (The complex readily forms a hydrate, which is not soluble in organic solvents. Consequently, protection from moisture is necessary.)... 

The azonitrile 19 also shows similar decomposition kinetics to AIBN (Table 3.2). The initiators 19 and AIBMe also have greater solubility in organic solvents than AIBN. 

Normally, persulfate (41) can only be used to initiate polymerization in aqueous or part aqueous (emulsion) media because it has poor solubility in most organic solvents and monomers. However, it has been reported that polymerizations in organic solvent may be initiated by crown ether complexes of potassium persulfate.234 237 Quaternary ammonium persulfates can also serve as useful initiators in organic media. 4 The rates of decomposition of both the crown ether complexes and the quaternary ammonium salts appear dramatically... 

The oxidation of alcohols is an important reaction in organic chemistry. While this transformation is traditionally performed in organic solvents, the use of aqueous orgarric solutions has just recently become a field of intense study (1-6). The effect of water on transition metal-catalyzed reactions, however, remains widely unexplored as most of these reactions require dry organic solvents to avoid decomposition of the transition metal catalyst, of water sensitive reagents, and/or intermediates by a nucleophilic attack of water (1). Comparative studies focusing on the effect of water as a co-solvent on the catalyst and the proceedings of a reaction are therefore rare (7). 

The decomposition, either thermal or under N2, of [0(AuPR3)3]0Tf (R = Ph, Me) in organic solvents has been studied the phosphine acts as an efficient oxygen trap and gold nanoparticles are produced.2727... 

Metallic powders are made several different ways. They can be prepared by reducing salts in a stream of a reducing gas, such as hydrogen chlorides of metals are commonly used but oxides are used too. Thermal decomposition in a vacuum of metal carbonyls or metal salts of organic acids, such as formates, produces metal powders. Surface areas of such powders are around 1.5 m2/g. Powders can also be made from electrolytic reduction of salts in organic solvents and by atomization of the metal. 

The reactive crystallization has some peculiar characteristics like insoluble product, initiation of reaction by change in pH and conductivity. In this case the solution becomes saturated and eventually supersaturated with respect to reactant nucleation [30], The ultrasound assisted decomposition precursors includes dissolving metal organic precursors in organic solvents/water with the assistance of surfactants leads to monodisperse and reduced metal/metal oxide nanoparticles. 

Silver perchlorate forms solid complexes with aniline, pyridine, toluene, benzene and many other aromatic hydrocarbons [1], A sample of the benzene complex exploded violently on crushing in a mortar. The ethanol complex also exploded similarly, and unspecified perchlorates dissolved in organic solvents were observed to explode [2], Solutions of the perchlorate in benzene are said to be dangerously explosive [3], but this may be in error for the solid benzene complex. The energy released on decomposition of the benzene complex has been calculated as 3.4 kJ/g, some 75% of that for TNT [4],... 

Another example of a transannular cyclization that occurs in the solid state is provided by the epoxy alcohol 31. This compound is stable when dissolved in organic solvents and in 0.25N sulfuric acid. However, the crystals transform rapidly to 32. Although the process is accompanied by partial melting, it appears to be a true solid-state one. Interestingly, the reaction is slowed down appreciably when the dry crystals are covered with ether. Hydrogen bromide is eliminated in the reaction and it may be that an acid-catalyzed process is also occurring in the presence of solvent this process may be slowed down by the dissolution of the decomposition products in the solvent (77). 

Fluorinated poly(imide-ether-amide)s are readily soluble in organic solvents like dimethylformamide (DMF), N-methylpyrrolidone (NMP), pyridine or tetrahydrofu-ran (THF) and give flexible films by casting of such solutions. These polymers exhibit decomposition temperatures above 360°C, and glass transition temperatures in the 221-246° C range. The polymer films have a low dielectric constant and tough mechanical properties. 

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