Aqueous carbonation reaction

Other Coordination Complexes. Because carbonate and bicarbonate are commonly found under environmental conditions in water, and because carbonate complexes Pu readily in most oxidation states, Pu carbonato complexes have been studied extensively. The reduction potentials vs the standard hydrogen electrode of Pu(VI)/(V) shifts from 0.916 to 0.33 V and the Pu(IV)/(III) potential shifts from 1.48 to -0.50 V in 1 Tf carbonate. These shifts indicate strong carbonate complexation. Electrochemistry, reaction kinetics, and spectroscopy of plutonium carbonates in solution have been reviewed (113). The solubiUty of Pu(IV) in aqueous carbonate solutions has been measured, and the stabiUty constants of hydroxycarbonato complexes have been calculated (Fig. 6b) (90). 

Benniston AC, Haniman A (2008) Artificial photosynthesis. Materials Today 11 26-34 Inoue T, Fujishima A, Konishi S, Honda K (1979) Photoelectrocatalytic reduction of carbon dioxide in aqueous suspensions of semiconductor powders. Nature 277 637-638 Halmann M (1978) Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature 275 115-116 Heminger JC, Carr R, Somorjai GA (1987) The photoassisted reaction of gaseous water and carbon dioxide adsorbed on the SrH03 (111) crystal face to form methane. Chem Phys Lett 57 100-104... 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

Although it was initially believed that polyacetylene was unstable in contact with water under all conditions, it has been successfully chemically doped in aqueous solutions with no apparent degradation of the material [82] and its electrochemistry has also been investigated [135-137] from which it is clear that no degradation occurs in concentrated aqueous electrolytes. Reaction with water can occur under some circumstances however giving rise to sp3 carbons and carbonyl-type structures [129, 138-141],... 

The Ni/Re on carbon catalyst was also evaluated in a 1700 hour continuous reactor test to determine the stability of the catalyst. This test was performed with a different model compound than xylitol. Shown in Figure 5, the results from the lifetime test of the Ni/Re catalyst operated at constant process conditions sampled intermittently for 1700 hours. This shows that for a similar aqueous hydrogenation reaction deliberately operated to near completion, the catalyst retained its activity and product selectivity even in the face of multiple feed and H2 interruptions. We feel that this data readily suggests that the Ni/Re catalyst will retain its activity for xylitol hydrogenolysis. 

The imidazole carbamate group is more stable to hydrolysis in aqueous buffer than the NHS-carbonate group, which is similar in reactivity to an NHS ester. However, this means that the imidazole carbamate also is slower to react and couple with amines. NHS-carbonate reactions usually go to completion within 1-2 hours at room temperature, whereas imidazole carbamates typically require higher pH conditions and overnight incubations to get maximal yield of ligand coupling. 

Initiation with X = OH has been discussed earlier. Table 8.11 summarizes some of the aqueous-phase HO, chemistry in which OH is generated and reacts in the atmosphere. (Note that the rate constants for some of the aqueous phase reactions shown in Tables 8.10-8.16 depend on such factors as ionic strength see Chapter 5.D.) Involved with this chemistry is that of bicarbonate/carbonate, since OH reacts with these species as well (Table 8.12). It is interesting that, in contrast to the high reactivity of OH toward S(IV) in aqueous solutions, direct reactions of H02/02 with S(IV) do not appear to be important (Sedlak and Hoigne, 1994 Yermakov et al., 1995). 

Green River Formation of Colorado and in Pleistocene ash beds at Olduvai Gorge Tanzania was formed by reactions of aqueous carbonate species with nepheline in the sediment (Smith and Milton 1966). 

Since the Suzuki coupling of purine derivatives was covered by recent reviews,1 we only present a selection lfom these reactions. Xanthine (3,6-dihydropurine-2,6-dione) derivatives were coupled with different boronic acids, including styrylboronic acid, in the presence of the conventional tetrakis(triphenylphosphino)palladium catalyst and tripotassium phosphate as a mild base (8.1.), to obtain the appropriate 8-substituted xanthines in acceptable yield.4 The advantage of the use of anhydrous tripotassium phosphate as base over the classical aqueous carbonate or hydroxide reagents might be attributed to the sensitivity of the 8-halopurine core towards nucleophilic attack. 

CH3NH2 H2C03 (aq.). Muller6 measured the heat of reaction of 1 mole of aqueous methylamine with 1 mole of aqueous carbon dioxide. 

Ca(HC03)2 (aq.). Randall and White3 reviewed the data of Backstrom,3 Cameron and Brezeate,1 Cameron and Robinson,1 2 Cavazzi,1 Ehlert and Hempel,1 Engel,1 Haehnel,1 2 Johnston,3 Kendall,2 McCoy and Smith,1 Schloesing,1 Wells,1 and Frear, Johnston, and Kline,1 on the solubility of calcium carbonate in aqueous carbonic acid, and concluded that Q25=8.6 for the reaction, CaC03 (c, calcite)+C02 (g)+H20 (liq.) = Ca(HC03)2 (aq.). 

The pH-swing process, which was developed in Japan (and later also presented in a patent by Yogo et al. [60]) is another two-step aqueous carbonation process where at first the pH of the solution is lowered so as to enhance the extraction of divalent metal ions. In the second step, the pH is raised to enhance the precipitation of carbonates. A schematic representation of a process utilizing the pH-swing is shown in Figure 14.3 (taken from Ref. [61]), where the principal reactions... 

Nonetheless, the general understanding of magnesium and calcium carbonation reactions has improved significantly (see also the studies by Hanchen et al. [107-110] on the relative importance of process parameters such as temperature, C02 pressure and particle size distribution). Studies involving a three-step process of olivine carbonation, involving (i) dissolution of olivine (ii) precipitation of magnesite and (iii) precipitation of silica in an aqueous solution, were recently reported from Norway [69], where the process proceeds without chemical additives at 10-15 MPa and 403-523 K. No reaction rates were reported, however. 

Holcman, J., Bjergbakke, E., and Sehested, K., The importance of radical-radical reactions in pulse radiolysis of aqueous carbonate/bicarbonate, Proc. Tihany Symp. Radiat. Chem., 6(1), 149-153, 1987. 

When alkoxyl radicals contain a hydrogen atom at the neighboring carbon, a rapid 1,2-H-shift (k = 106 s"1 or even faster) occurs in aqueous solution [reaction (6) Berdnikov et al. 1972 Gilbert et al. 1976, 1977 Schuchmann and von Sonntag 1981] with a KIE = 50 in the CH3CH20 /CD3CD20 system (Bonifacic et al. 2003). 

Co(A2ODC)]2+ is easily reduced to the Co2+ complex in aqueous carbonate solution (1% v/v methanol). This reaction is photocatalyzed and induced by... 

The reaction sequence in steps two and three is known as the Corey-Fuchs method to create an alkyne from an aldehyde 10 Reaction of triphenylphosphane with carbontetrabromide gives phenylphosphane-dibromomethylene. This reagent then transforms aldehyde 19 into the corresponding dibromoalkene 20 thereby extending the chain by one carbon. Reaction of the bromo compound with two equivalents of n-butyllithium in THF at -78 °C results in the rapid formation of the acetylenic lithio derivative which forms the terminal acetylene 21 upon aqueous work-up. 

Depending on the reaction conditions, halogenation of thieno[2,3-Z>]pyridine (20) can lead to a variety of products resulting from substitution, addition, and oxidation reactions. 2,3-Dibromo-thieno[2,3-/)]pyridine is produced by the reaction of compound (20) with bromine in an aqueous carbon tetrachloride system and the 2,3-dichloro-2,3-dihydro derivative is formed from the same starting material upon treatment with chlorine in chloroform/water or with iodobenzene dichloride in aqueous acetonitrile (70JHC81, 71JHC931). 

The ring-opening tendency, assuming equal solubility in the reaction medium concerned, is controlled in general by the electron density at the C-2 or C-5 atom, which is largely dependent on the substituents, and by the nucleophilicity of the reactants. Ethanol, water, aqueous carbonate solution, ethoxide, ethanolic and aqueous hydroxide, ammonia, amines, hydrazines, hydrazides, hydrogen sulfide, and mineral acids have all been used as nucleophilic reagents. 

Description EO in an aqueous solution is reacted with C02 in the presence of a homogeneous catalyst to form ethylene carbonate (1). The ethylene carbonate subsequently is reacted with water to form MEG and C02 (3). The net consumption of C02 in the process is nil since all C02 converted to ethylene carbonate is released again in the ethylene carbonate hydrolysis reaction. Unconverted C02 from the ethylene carbonate reaction is recovered (2) and recycled, together with C02 released in the ethylene carbonate hydrolysis reaction. 

The majority of interest in cobalt(III) complexes of terpy has centered on the [Co(terpy)2] cation, although a few 1 1 complexes have been reported. A crystal structural analysis of the complex [Co(terpyXC03XOH)]-4H20, obtained by the reaction of [Co(terpy)2] with aqueous carbonate, has revealed the expected distorted octahedral geometry about the metal ion, with a bidentate chelating carbonate and meridional terpy ligands 287). The... 

The fact that stronger bases speed up both the coupling and the hydrolytic deboronation means that the choice of base is not always obvious. Although aqueous carbonate is the one most commonly used, stronger alkoxide bases appear to yield the best results for stericaUy hindered boronic acids. For base-sensitive substrates, bicarbonate can be used successfully when THF is the organic cosolvent. However, this base is less successful when employed with mostly nonaqueous reaction conditions. On the other hand, fluoride, an even weaker base, appears to work well with both aqueous and nonaqueous protocols. ... 

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