Metal hydroxide decomposition

There are some examples of the nanoparticle formation in polymers by metal hydroxide decomposition [102]. The thermal decay of silver hydroxide ammonia solution in the isotactic PP melt (temperature range 543-563 K in polymethylsiloxane) occurs according to the following scheme ... 

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

In order for a soHd to bum it must be volatilized, because combustion is almost exclusively a gas-phase phenomenon. In the case of a polymer, this means that decomposition must occur. The decomposition begins in the soHd phase and may continue in the Hquid (melt) and gas phases. Decomposition produces low molecular weight chemical compounds that eventually enter the gas phase. Heat from combustion causes further decomposition and volatilization and, therefore, further combustion. Thus the burning of a soHd is like a chain reaction. For a compound to function as a flame retardant it must intermpt this cycle in some way. There are several mechanistic descriptions by which flame retardants modify flammabiUty. Each flame retardant actually functions by a combination of mechanisms. For example, metal hydroxides such as Al(OH)2 decompose endothermically (thermal quenching) to give water (inert gas dilution). In addition, in cases where up to 60 wt % of Al(OH)2 may be used, such as in polyolefins, the physical dilution effect cannot be ignored. 

Stannic and stannous chloride are best prepared by the reaction of chlorine with tin metal. Stannous salts are generally prepared by double decomposition reactions of stannous chloride, stannous oxide, or stannous hydroxide with the appropriate reagents. MetaUic stannates are prepared either by direct double decomposition or by fusion of stannic oxide with the desired metal hydroxide or carbonate. Approximately 80% of inorganic tin chemicals consumption is accounted for by tin chlorides and tin oxides. 

Bismuth trioxide may be prepared by the following methods (/) the oxidation of bismuth metal by oxygen at temperatures between 750 and 800°C (2) the thermal decomposition of compounds such as the basic carbonate, the carbonate, or the nitrate (700—800°C) (J) precipitation of hydrated bismuth trioxide upon addition of an alkah metal hydroxide to a solution of a bismuth salt and removal of the water by ignition. The gelatinous precipitate initially formed becomes crystalline on standing it has been represented by the formula Bi(OH)2 and called bismuth hydroxide [10361 -43-0]. However, no definite compound has been isolated. 

The aqueous decomposition of thiourea to sulfide and cyanamide has been found to be catalyzed by metal hydroxide species and colloidal metal hydroxide precipitates. Kitaev suggested that Cd(OH)2 is actually required for CdS film formation to occur by adsorption of thiourea on the metal hydroxide particles, followed by decomposition of the Cd(OH)2-thiourea complex to CdS. Kaur et al. [241] found... 

The metal and ammonium salts of dithiophosphinic acids tend to exhibit far greater stability with respect to this thermal decomposition reaction, and consequently these acids are often prepared directly in their salt form for convenience and ease of handling. Alkali-metal dithiophosphinates are accessible from the reaction of diphosphine disulfides with alkali-metal sulfides (Equation 22) or from the reaction of alkali-metal diorganophosphides with two equivalents of elemental sulfur (Equation 23). Alternatively, they can be prepared directly from the parent dithiophosphinic acid on treatment with an alkali-metal hydroxide or alkali-metal organo reagent. Reaction of secondary phosphines with elemental sulfur in dilute ammonia solution gives the dithiophosphinic acid ammonium salts (Equation 24). 

MgO- and Ag-modified membranes were obtained by homogeneous precipitation of the hydroxide from a typical solution consisting of 0.75 M urea and 0.2-0.5 M AgN03 or Mg(NOj)2 in water. The solution is introduced into the pores of the support and/or the y-alumina top layer by impregnation. An increase in temperature results in (I) evaporation of the solvent and concentration of the solution and (2) the decomposition of urea (at T > 90°C) resulting in the formation of NH3 and a decrease in the pH followed by precipitation of the metal hydroxide. The hydroxide is next converted to the oxide form at 350-450°C. 

Another type of reaction is double decomposition producing metal hydroxides. Thus, insoluble heavy metal hydroxides may be precipitated by treating caustic soda with a soluble metal salt ... 

The mechanisms of CD processes can be divided into two different processes formation of the required compound by ionic reactions involving free anions, and decomposition of metal complexes. These two categories can be further divided in two formation of isolated single molecules that cluster and eventually form a crystal or particle, and mediation of a solid phase, usually the metal hydroxide. We consider first the pathways involving free anions and defer to later those where a metal complex decomposes. 

Double decomposition by NH4OH. A metallic hydroxide may precipitate, insoluble in excess of ammonium hydroxide or ammonium salts. Examples in analytical chemistry are the precipitation of the hydroxides of iron and aluminum... 

Reducing sugars are decomposed by sodium hydroxide in boiling butanol. Treatment of reducing sugars with alcoholic alkali metal hydroxide must, therefore, be conducted at room temperature, in order to avoid this decomposition of the carbohydrate. 

The formation of ammonia always takes place. When heated with metal hydroxides some ketoximes partially regenerate ketones to liberate ammonia (54MI1). Nevertheless, cyclohexanone does not seem to be an intermediate product since, in a special run carried out with a mixture of cyclohexanone and ammonia (under otherwise equal conditions), a complicated mixture of products, containing no alcohol 110 was obtained. Cyclohexanone itself was nearly inert in runs with LiOH, NaOH and tetrabutylammonium hydroxide, which provides evidence against its formation as an intermediate in the alkaline decomposition of the oxime. 

The ways in which metal nitrates, carbonates, oxides and hydroxides decompose can also be discussed in terms of the reactivity series of the metals. The decomposition processes are different, depending on the position of the metal in the reactivity series. 

Pretreatment involving filtration and clarification for removal of suspended solids and turbidity may improve treatment efficiency. To reduce the interference of inorganic and organic compounds, other treatment processes may have to be combined with UV/H202 systems for effective treatment. In some situations, pH control may be required to prevent precipitation of metal salts during the oxidation process and to avoid a loss in efficiency due to the precipitates. Generally, metal hydroxide precipitation can be avoided for pH less than 6. Alkaline pH can adversely affect the reaction rate, possibly due to the base-catalyzed decomposition of H202. 

All of these complexes decompose cleanly at low temperature to produce acetonitrile, carbon dioxide, and initially, the metal hydroxide (equation 45). The decomposition temperatures are 144,176, and 198 °C for Ba, Cu, and Y, respectively. In the case of copper and yttrium, the final product is the metal oxide produced by the dehydration of the hydroxide, while barium hydroxide recombines with carbon dioxide to yield the carbonate. Barium carbonate formation can be avoided, however, by use of a different ligand that avoids carbon dioxide formation. Benzoin a-oxime (Hbo) (13) has been found to be a quite suitable diprotic ligand for this purpose. The barium salt is easily prepared by reaction of the oxime with the metal dihydride (equation 46), and it decomposes cleanly to barium oxide by loss of benzaldehyde and benzonitrile at 250 °C (equation 47). 

The reactions in the decomposition of 13,6-trimethyl-2-oxo-l, 2-dihydropyrazine methiodide with alkali metal hydroxide to give 1,4,6-trimethyl-3-methylene-2-oxo-1,2,3,4-tetrahydropyrazine (1105) and its reaction with benzenediazonium chloride or phenylhydrazine to give l,4,6-trimethyl-2-oxo-3-phenylazomethylene-l,2,3,4-tetrahydropyrazine (1105,1132) have been described. 

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