Carbonates chemistry

Limestone (chiefly calcite, CaCOa) and dolomite rocks (chiefly dolomite, CaMg(C03)2) are exposed at about 20% of Earth s surface. Carbonate detritus, fossil shell materials, and carbonate cements are also common in noncarbonate sedimentary rocks and arid-climate soils. The carbonate minerals found in such occurrences, in decreasing order of importance, are calcite, dolomite, magnesian cal-cites (Cai jMgfCOa where jc is usually 0.2), aragonite (a CaCOa polymorph) and, perhaps, magnesite. As a rule of thumb, when such materials are present in silicate or aluminosilicate rocks or soils at a level of about 1 % or more, they will lend to dominate the chemistry of the soil or ground-water. This fact is extremely important when one is concerned about the ability of a rock to neutralize acid mine waters, other acid wastewaters, or acid rain. 

Vaterite is a rare mineral that only forms from solutions highly supersaturated with respect to calcite and aragonite, Ogino et al. (1987) precipitated vaterite with calcite between 14 and 30°C from laboratory solutions in which the fCa ]lCOa ] product equaled about 10 . The vaterite was transformed to calcite in several hours. 

TABLE 6.1 Solubility product expressions and fsp values for some minerals in the system Ca0-Mg0-C02 S03-H20 at 25 C and 1 bar total pressure 

Phase relations in the system Ca0-C02-H20 from 0 to 100°C are shown in Fig. 6.1. Given the fact that CO2 pressures in natural environments are rarely less than about 10 bar, and that equilibrium between calcite and portlandite is at a CO2 pressure of ]0 bar at 25°C, calcite is clearly the stable phase in Earth-surface environments. 

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The free radicals that we usually see in carbon chemistry are much less stable than these Simple alkyl radicals for example require special procedures for their isolation and study We will encounter them here only as reactive intermediates formed m one step of a reaction mechanism and consumed m the next Alkyl radicals are classified as primary secondary or tertiary according to the number of carbon atoms directly attached to the carbon that bears the unpaired electron... 

Although Kekule and Couper were correct in describing the tetravalent nature of carbon, chemistry was still viewed in a two-dimensional way until 1874. In that year, Jacobus van t Hoff and Joseph Le Bel added a third dimension to our ideas about organic compounds when they proposed that the four bonds of carbon are not oriented randomly but have specific spatial directions. Van t Hoff went even further and suggested that the four atoms to... 

Where do we find the enormous quantities of carbon and carbon compounds needed to feed this giant industry Let s begin our study of carbon chemistry by taking a look at the chief sources of carbon and carbon compounds. 

Molten salt extraction residues are processed to recover plutonium by an aqueous precipitation process. The residues are dissolved in dilute HC1, the actinides are precipitated with potassium carbonate, and the precipitate redissolved in nitric acid (7M) to convert from a chloride to a nitrate system. The plutonium is then recovered from the 7M HNO3 by anion exchange and the effluent sent to waste or americium recovery. We are studying actinide (III) carbonate chemistry and looking at new... 

The seminal studies on these complex compounds were conducted by Alfred Werner in an intensive period of work at the turn of the century. A typical example of the problems that Werner addressed lies in the various compounds which can be obtained containing cobalt, ammonia and chlorine. Stable and chemically distinct materials with formulations Co(NH3) Cl3 (n = 4,5 or 6) can be isolated. The concepts of valency and three-dimensional structure in carbon chemistry were being developed at that time, but it was apparent that the same rules could not apply to... 

Two other, closely related, consequences flow from our central proposition. If the d orbitals are little mixed into the bonding orbitals, then, by the same token, the bond orbitals are little mixed into the d. The d electrons are to be seen as being housed in an essentially discrete - we say uncoupled - subset of d orbitals. We shall see in Chapter 4 how this correlates directly with the weakness of the spectral d-d bands. It also follows that, regardless of coordination number or geometry, the separation of the d electrons implies that the configuration is a significant property of Werner-type complexes. Contrast this emphasis on the d" configuration in transition-metal chemistry to the usual position adopted in, say, carbon chemistry where sp, sp and sp hybrids form more useful bases. Put another way, while the 2s... 

Takahashi, T., Broecker, W. S., Werner, S. R, and Bainbridge, A. E. (1980). Carbonate chemistry of the surface waters of the world oceans. In "Isotope Marine Chemistry" (E. P. Goldberg, Y. Horibe and K. Sarubashi, eds), pp. 291-326. Uchida Rokakuho, Tokyo. 

The pentacoordinate intermediate is the analog of the tetrahedral intermediate, and stable phosphoranes are the analogs of ortho esters and related species in carbon chemistry. Ph3P(OPh)2 and P(OPh)5 were reported in 1959, and in 1958 a general synthesis of pentaalkoxy phosphoranes containing an unsaturated five-membered ring was reported. In 1964 a synthesis of pentaethoxyphosphorane was devised which led to the preparation of a number of saturated and unsaturated pentaalkoxy... 

Recent study of silenes has clearly established their ability to act as dienophiles in [2 + 4] Diels-Alder-type reactions involving 1,3-dienes. However, it has also been clearly demonstrated that products of the ene reaction commonly accompany the [2 + 4] cycloadducts and may on occasion be the major products. In addition, unlike those in carbon chemistry, [2 + 2] cycloadditions are often observed to occur in competition with the above processes—not only from reactions of silenes with dienes... 

Bucky balls (football molecules) were only discovered in 1985 and named fullerene after the architect Buckminster-Fuller. The Nobel Prize for chemistry in 1996 was awarded for this new carbon chemistry. Molecular tubes with this structure have particularly interesting properties. 

Kirmse, W. Carbone Chemistry. New York Academic Press 1967. 

Despite the increasing interest in understanding the phenomena of bonding in silicon compounds, there are, until now, no well established and commonly accepted theories. Silicon compounds are mainly discussed in terms of carbon chemistry. Thus, specific properties of silicon compounds are usually compared with those of the corresponding carbon homologues. In this report some important features of silicon compounds are developed by means of ab initio calculations. From this a set of basic rules will be presented by which more complex phenomena can be explained in turn. 

Ahmad R, Kookana R, Alston A, Skjestad J (2001) The nature of soil organic matter affects sorption of pesticide. 1. Relationships with carbon chemistry as determined by C-13 CPMAS NMR spectroscopy. Environ Sci Technol... 

Lackner, K.S., Carbonate chemistry for sequestering fossil carbon, Ann. Rev. Energy Environ., 27(1), 193, 2002. 

Teyssier D., Fossd D., Gerin, M., et al. (2004). Carbon budget and carbon chemistry in photon dominated regions. Astronomy Astrophysics 417 135. 

Beginning as chemical curiosities, carbenes are now solidly established as reactive intermediates with fascinating and productive research areas of their own. Six decades of divalent carbon chemistry have provided us with a vast repertoire of new, unusual, and surprising reactions. Some of those reactions, once classified as exotic, have become standard methods in organic synthesis. These highly reactive carbene species have been harnessed and put to work to achieve difficult synthetic tasks other reactive intermediates cannot easily perform. 

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