Solutions describing reactions

The synthesis described met some difficulties. D-Valyl-L-prolyl resin was found to undergo intramolecular aminoiysis during the coupling step with DCC. 70< o of the dipeptide was cleaved from the polymer, and the diketopiperazine of D-valyl-L-proline was excreted into solution. The reaction was catalyzed by small amounts of acetic acid and inhibited by a higher concentration (protonation of amine). This side-reaction can be suppressed by adding the DCC prior to the carboxyl component. In this way, the carboxyl component is "consumed immediately to form the DCC adduct and cannot catalyze the cyclization. 

The processes of complex-ion formation referred to above can be described by the general term complexation. A complexation reaction with a metal ion involves the replacement of one or more of the coordinated solvent molecules by other nucleophilic groups. The groups bound to the central ion are called ligands and in aqueous solution the reaction can be represented by the equation ... 

In solution this reaction is rather rapid but in the solid state autoxidation takes place much slower. Nevertheless, commercial sulfides and polysulfides of the alkali and alkali earth metals usually contain thiosulfate (and anions of other sulfur oxoacids) as impurities [6]. For all these reasons the chemistry of polysulfides is rather complex, and some of the earlier studies on polysulfides (prior to ca. 1960) are not very rehable experimentally and/or describe erroneous interpretations of the experimental results. 

We can think of the oxygen transfer from the lung to the blood as a simple chemical reaction molecules of gas strike the alveoli. By analogy with simple solution-phase reactions, the rate equation describing the rate at which oxygen enters the blood is formulated according to... 

Given the disparity in success between raw and purified NaNT solutions described in the previous section, it was hypothesized that an impurity in the raw NaNT solution was contributing towards varying DBX-1 reaction results including the inability to produce DBX-1 at all. NaNT synthesis has never been optimized for scale-up nor have adequate analytical methods been developed to analyze NaNT. The investigating teams from Nalas Engineering and Pacific Scientific utilized various analytical methods to identify impurities in the NaNT solutions that impeded the reaction to DBX-1. 

Many models, which could be classified as "surface complexation models (6-8)," have been used to describe reactions at the oxide-solution interface. Although there are differences in the way these models are formulated, they all have two features in common ... 

It should be pointed out that one cannot expect quantitatively correct data from such calculations. Clearly, the complexes considered do not appropriately represent real solutions. Most of the results obtained could have been guessed equally well by chemical experience and intuition anyway we expect ions to be more strongly hydrated than neutral molecules. In the actual calculations, the method employed is known to overemphasize the expected effects. The merits of attempts like the ones mentioned axe therefore not to be found in the realization of quantitative results, but verify that our expectations are definitely reproducable in terms of quantum chemical data, and they demonstrate how such calculations could be made. There have also been attempts to describe reactions of solvated molecules by an MO theoretical treatment for the two reaction partners, with inclusion of the solvent by representing it as point dipoles. As a first step, Yamabe et al. 186> performed ab initio calculations on the complex NH3.HF, solvating each of the partners by just one point dipole. A study of MO s of the interacting complex with and without dipoles shows that the latter has a favorable effect on the proceeding of the reaction. 

Where ki to k7 values are in M" s, k and k values were only known approximately as a result, different stages in the Fenton s reagent were described as follows reactions (1) and (2) will take place in a solution containing an excess of Fe with respect to H2O2. With excess of hydrogen peroxide in acid solution, when reactions (5) and (6) can be neglected, reactions (1), (3) and (7) occur. Comparable concentrations of Fe and H2O2 in acid media result in reactions (1), (2), (3) and (7). 

The released U(VI) from the U()2 matrix will continue to be dissolved until saturation with secondary U(VI) solid phases is reached. The observations from both laboratory and natural systems would indicate that the kinetically preferred phase is hydrated schoepite. This will be denoted as U02(0H)2(s) for the sake of description of the model, although the correct notation would be U03-xH20, with x oscillating between 0 and 2. Depending on the presence of carbonates in the contacting solution, the reactions can be described as ... 

Here, the term no-solvent means the absence of a traditional solvent—the reactants are neat and may well be sohds. Where one reactant is in sufficiently large excess to qualify as a solvent, for example in Friedel-Crafts alkylations or acylations with excess benzene or toluene, the reactions are not normally classified as no-sol-vent. The phrase solid-phase (solid-state) reaction today often describes a reaction carried out on a solid phase, like a resin, to which the reaction intermediates are bound by adding reagents in solution. These reactions have become very important in combinatorial chemistry, but they do not meet the definition of no-solvent. The nosolvent reactions refer only to the primary reactions themselves and not to workup conditions which may or may not involve solvents (Dittmer, 1997). 

Identification of Reaction Products. Carbon dioxide-free air was bubbled through the previously described reaction mixture. At the end of 6 hours, the carbon was removed by filtration, and the filtrate poured slowly into six times its volume of ethanol (95%). The precipitate which formed was recrystallized first from an ethanol-water solution and finally from a minimum amount of water. 

Another derivation has been given by Resibois and De Leener. In principle, eqn. (287) can be applied to describe chemical reactions in solution and it should provide a better description than the diffusion (or Smoluchowski) equation [3]. Reaction would be described by a spatial- and velocity-dependent term on the right-hand side, — i(r, u) W Sitarski has followed such an analysis, but a major difficulty appears [446]. Not only is the spatial dependence of the reactive sink term unknown (see Chap. 8, Sect. 2,4), but the velocity dependence is also unknown. Nevertheless, small but significant effects are observed. Harris [523a] has developed a solution of the Fokker—Planck equation to describe reaction between Brownian particles. He found that the rate coefficient was substantially less than that predicted from the diffusion equation for aerosol particles, but substantially the same as predicted by the diffusion equation for molecular-scale reactive Brownian particles. 

When two or more substances are mixed together in a manner that is homogeneous and uniform at the molecular level, the mixture is called a solution. The component (usually a liquid) that is present in much larger quantity than the others is called the solvent the other components are the solutes. The concentration of a solution describes the amount of solute present in a given amount of solution. When a solution is involved in a reaction, the stoichiometric calculations must take into account two quantities not previously discussed the concentration of the solution, and its volume. 

We have been interested in developing new routes to mesostructured metal sulfides. Our approach capitalizes on well-established solution condensation reactions that can transform discrete, soluble metal thiolate species into solid-state metal sulfide compounds. Here we wish to describe the use of (NH4)2WS4 as a precursor material in the synthesis of three mesostructured tungsten suldifes with the inorganic walls that consist of continuous WS3 chains and WS2. 

The liquid sulfur dioxide solutions described in the preparations have a vapor pressure of about 3.3 atm at 21 °C. Therefore, well-constructed glass vessels and a glass (or metal) vacuum line must be employed to prevent pressure bursts. Thick leather gloves, safety goggles, a face shield, and a rubber apron should be worn and the experiments have to be conducted behind a safety shield or explosion-proof glass in a fume hood to prevent possible contact with the reaction mixtures as well as with AsF5 and SbFs. 

Rh6(CO)16 (107 mg, 0.1 mmol) is dissolved completely in a mixture of tri-chloromethane (150 mL) and acetonitrile (10 mL). A solution of trimethylamine /V-oxide (Me3N0-2H20) (12 mg, 0.11 mmol) in MeOH/CHCl3 (0.5/5.0 mL) is added dropwise under vigorous stirring to the cluster solution. The reaction mixture is allowed to stand for an additional 15 min. The product is isolated by the procedure described above. Yield of 70-75 mg of Rh6(CO)15NCMe 64-70%. 

A number of situations may be visualized. Electron transfer may take place between a pair of redox proteins in solution. Certain reactions in the cytoplasm of the red blood cell fall into this category, such as that between hemoglobin and cytochrome b reductase. These reactions will probably occur by an outer-sphere mechanism, as was described earlier for model reactions between isolated electron-transfer proteins and also between these proteins and simple complexes. Interaction between such proteins probably utilizes specific charged areas on their surfaces. The possibility of inner-sphere reactions may have to be considered in a few cases. 

---