Carbonates alkali metals

As with the hydroxides, we find that whilst the carbonates of most metals are insoluble, those of alkali metals are soluble, so that they provide a good source of the carbonate ion COf in solution the alkali metal carbonates, except that of lithium, are stable to heat. Group II carbonates are generally insoluble in water and less stable to heat, losing carbon dioxide reversibly at high temperatures. 

Compound 9 has been prepared by the latter authors using triethylene glycol diiodide and triethylene glycol diamine (see Eq. 4.11) and an alkali metal carbonate in acetonitrile solution. ... 

Reaction of NbC F with an alkali metal carbonate, M2CO3, yields carbon dioxide, C02, in an amount equivalent to that of a chemical compound forming at the first stage of the reaction. The general form of the reaction between niobium dioxyfluoride and an alkali metal carbonate, M2C03, is ... 

When the reaction is performed at relatively low temperatures that prevent strong thermal decomposition of the alkali metal carbonate, the formation of C02 will be related only to the reaction and will indicate the stoichiometry of the process. Fig 8 presents mass loss isotherms of Nb02F - M2CO3 mixtures (in which M - Li, Na, K, Rb, Cs) that were subjected to thermal treatment in air at 850°C [84, 85]. It is important to mention that parallel experiments performed without the addition of Nb02F, resulted in alkali metal carbonate mass losses that were in the same order of magnitude as the measurement errors at temperatures below 850°C. 

In mixtures containing excessive amounts of alkali metal carbonates (molar ratios of M2C03 Nb02F equal to 4 1, 3 1 and 2 1), orthoniobate or a mixture of ortho- and metaniobate and alkali metal fluorides were found. A subsequent increase in the Nb02F concentration in the initial mixture leads to the... 

Analysis of the composition of compounds formed in systems containing Nb02F and alkali metal carbonates reveals several common peculiarities. The first stage of the interaction takes place according to Equation (11) and can be formulated in general as follows ... 

The apparently high relative stability of KF-4KNb03 can be related to the steric similarity between potassium and fluorine ions, which is hardly the case with other alkali metals. Table 10 presents a general list of compounds that can be obtained by the interaction of Nb02F with alkali metal carbonates. 

The compound formed in the first step of the reaction between the solid components and the molten alkali metal carbonate can passivate the surface and prevent subsequent development of the interaction. This special property of M4Me04F, the compound formed in the first step, leads, in effect, to a single-stage interaction. 

Summarizing the above results, the following peculiarities of the interactions of niobium and tantalum compounds with alkali metal carbonates can be mentioned ... 

Alkali metal carbonates interact in molten form ... 

Amorphous or crystalline silicon both react exothermally when heated with alkali-metal carbonates, attaining incandescence and evolving carbon monoxide. 

Titanium powder has ignited as a thin layer under carbon dioxide, and bums in the gas above 550°C [1]. Contact of titanium with fused alkali-metal carbonates causes incandescence [2],... 

Contact of powdered titanium with molten potassium chlorate, alkali-metal carbonates or mixed potassium carbonate/nitrate causes vivid incandescence. 

This section is limited to complexes which have a group 1 metal in conjunction with another, different main group metal, but also includes Cu and Cd since they exhibit properties akin to their main group analogs. It is also limited mainly to those complexes in which the metals find themselves attached to different atoms and there is a particular emphasis on compounds with alkali metal-carbon bonds of various types, except where the evolution of inverse crown complexes is discussed. There are many more heterobimetallic-heteroatom complexes (e.g., mixed metal amides), but these lie outside the scope of this current review though references may be found to them in the references for the complexes described herein. 

Aqueous or methanolic solutions of alkali metal carbonates induce disproportionation of chalcogens to oxoanions and polychalcogenides E under solvothermal conditions.11 Potential redox equilibria such as (1) are driven to the right at 120-200°C by the development of C02. 

The choice of base used in the Ter Meer reaction is important for two reasons. First, studies have found that strong bases, such as alkali metal hydroxides, inhibit the reaction and promote side-reactions, whereas the weaker alkali metal carbonates generally give higher yields.Secondly, if the m-nitronitronate salt needs to be purified by filtration it should be sparingly soluble in the reaction solvent and both the reaction solvent and the counterion of the gm-nitronitronate salt affect this solubility. Use of the potassium salt is advantageous for aqueous systems where the em-nitronitronate salts are usually only sparingly soluble, whereas the sodium salt can be used for nonaqueous reactions. 

In a similar manner, of the isomeric trinitrobenzenes, only the symmetrical 1,3,5-isomer shows sufficient chemical stability for use as an explosive. Even so, the aromatic ring of 1,3,5-trinitrobenzene is highly electron deficient and reaction with alkali metal carbonates or bicarbonates in aqueous boiling methanol yields 3,5-dinitroanisole. Unsymmetrical isomers of trinitrobenzene are much more reactive than the 1,3,5-isomer, with only relatively mild conditions needed to effect the displacement of their nitro groups. ... 

Peterson and Scarrah 165) reported the transesterification of rapeseed oil by methanol in the presence of alkaline earth metal oxides and alkali metal carbonates at 333-336 K. They found that although MgO was not active for the transesterification reaction, CaO showed activity, which was enhanced by the addition of MgO. In contrast, Leclercq et al. 166) showed that the methanolysis of rapeseed oil could be carried out with MgO, although its activity depends strongly on the pretreatment temperature of this oxide. Thus, with MgO pre-treated at 823 K and a methanol to oil molar ratio of 75 at methanol reflux, a conversion of 37% with 97% selectivity to methyl esters was achieved after 1 h in a batch reactor. The authors 166) showed that the order of activity was Ba(OH)2 > MgO > NaCsX zeolite >MgAl mixed oxide. With the most active catalyst (Ba(OH)2), 81% oil conversion, with 97% selectivity to methyl esters after 1 h in a batch reactor was achieved. Gryglewicz 167) also showed that the transesterification of rapeseed oil with methanol could be catalyzed effectively by basic alkaline earth metal compounds such as calcium oxide, calcium methoxide, and barium hydroxide. Barium hydroxide was the most active catalyst, giving conversions of 75% after 30 min in a batch reactor. Calcium methoxide showed an intermediate activity, and CaO was the least active catalyst nevertheless, 95% conversion could be achieved after 2.5 h in a batch reactor. MgO and Ca(OH)2 showed no catalytic activity for rapeseed oil methanolysis. However, the transesterification reaction rate could be enhanced by the use of ultrasound as well as by introduction of an appropriate co-solvent such as THF to increase methanol solubility in the phase containing the rapeseed oil. 

The precipitate is filtered and dried at 100°C. If an alkali metal carbonate is used instead of ammonium carbonate, a hydrated basic carbonate is obtained which upon heating with ammonium chloride at 150°C in the absence of air produces anhydrous carbonate. 

Nickel carbonate forms many double salts, such as, Na2COs NiCOs IOH2O with alkali metal carbonates. However, such double carbonates usually are prepared by mixing an alkali metal or ammonium bicarbonate solution with a nickel salt solution, followed by crystallization. 

Rubidium also may be recovered by the chlorostannate method. In this method the alkali metal carbonate solution obtained from the mixed alum is treated with carbon dioxide. Most potassium is precipitated as bicarbonate, KHCO3. Addition of hydrochloric acid converts the carbonates to chlorides. The chlorides are converted to chlorostannates by carefully adding stoichiometric quantities of stannic chloride at pH just below 7 ... 

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