Alkali reversible equilibria

Reduction under nitrogen of totracarbonyl nickel with alkali metals or sodium and lithium amalgams (71) in THF, or with alkali hydroxides in methanol, gives a mixture of the dianions [Ni5(CO) 42]2- and pMi6(CO) i2]2 (28, 95). The final composition of the reaction mixture greatly depends on the experimental conditions owing to the easily reversed equilibrium ... 

We postulate a reversible equilibrium between glycogen or glucose and lactic add, maintained by enzymes. This permits of glucose being converted into dextrorotatory or laevorotatory acid, depending on the nature of the enzyme, and requires the formation of optically neutral lactic add when the reaction is caused or catalyzed by alkali, as in the experiments by Evans. These predictions have been fulfilled experimentally. 

Heating a crystal of alkali halide containing dissolved alkali metal in hydrogen discharges the colour of the crystal and causes the absorption spectrum to change (13). A new peak occurs in the ultra-violet. These centres, which are usually designated as 7-centres, are in a reversible equilibrium with... 

The alkali metal allyl compounds show splittings that are one order of magnitude smaller. No temperature-dependence was reported or is evident from comparison of different investigations. It was concluded that the allyl magnesium bromide has a o-covalent unsymmetrical structure with a monohapto ligand-metal interaction. A fast, reversible equilibrium (33) interconverts structure [26a] and its tautomeric structure [26b]. In contrast the alkali metal allyl compounds can be described as more or less symmetric 7t-complexes [26c] with trihapto interaction between metal and ligand. 

It should be noted that the highest possible absorption rates will occur under conditions in which the hquid-phase resistance is negligible and the equilibrium back pressure of the gas over the solvent is zero. Such situations would exist, for instance, for NH3 absorption into an acid solution, for SO9 absorption into an alkali solution, for vaporization of water into air, and for H9S absorption from a dilute-gas stream into a strong alkali solution, provided there is a large excess of reagent in solution to consume all the dissolved gas. This is known as the gas-phase mass-transfer limited condition, wrien both the hquid-phase resistance and the back pressure of the gas equal zero. Even when the reaction is sufficiently reversible to allow a small back pres-... 

Griess (1864a) had already observed that the diazo compounds obtained from primary aromatic amines in acid solution are converted by alkalis into salts of alkalis. The reaction is reversible. The compounds which Hantzsch (1894) termed sjw-diazotates exhibit apparently the same reactions as the diazonium ions into which they are instantaneously transformed by excess of acid. Clearly the reaction depends on an acid-base equilibrium. 

Since the synthesis temperatures are higher than the dissociation temperatures of the phases that are formed (at a pressure of lO N m ), it is necessary to react the alkali metal with boron under metal pressure in excess of that defined by Eq. (a), in sealed vessels. The alkali metal is present as a liquid in equilibrium with the vapor phase, the pressure of which is determined by the T of the coldest point. This pressure (greater the more volatile the metal) favors the synthetic reaction relative to the reverse dissociation reaction. 

The immobilization of dissolved chemical species by adsorption and ion exchange onto mineral surfaces is an important process affecting both natural and environmentally perturbed geochemical systems. However, sorption of even chemically simple alkali elements such as Cs and Sr onto common rocks often does not achieve equilibrium nor is experimentally reversible (l). Penetration or diffusion of sorbed species into the underlying matrix has been proposed as a concurrent non-equilibration process (2). However, matrix or solid state diffusion is most often considered extremely slow at ambient temperature based on extrapolated data from high tem-... 

In a perfectly-buffered solution the SO2 vapor pressure will be directly proportional to the total concentration of SO2 and bisulfite, giving a linear equilibrium relationship. In simple alkali sulfite solution without added buffer, the equilibrium relationship is highly nonlinear, because H-1" accumulates as SO2 is absorbed. Under these conditions is it not possible to carry out reversible SO2 absorption/stripping in a simple system, resulting in greater steam requirements than expected with a linear equilibrium relationship. Weak acid buffers such as sodium citrate have been proposed to "straighten" the equilibrium relationship and thereby reduce ultimate steam requirements (Jl, 2, 7). Citrate buffer is attractive because it is effective over a wide range, from pH 2.5 to pH 5.5 in concentrated solutions. 

Equation 7 shows the interaction of ferricyanide and cobaltocyanide to form a binuclear complex as described by Haim and Wilmarth (4). It is probable that the hydrogen evolution noted occurs via displacement of the equilibrium shown in Equation 6. Equation 8 defines the role of alkali, the presence of which is required to effect the catalytic reduction of ferricyanide. The hydroxo complex so obtained may then undergo the reverse aging process shown in Equation 5 to reform cyanocobaltate(II), which then absorbs hydrogen. The over-all result is reduction of ferri- to ferrocyanide by hydrogen. 

Physical chemical studies of dilute alkali metal-ammonia solutions indicate the principal solution species as the ammoniated metal cation M+, the ammoniated electron e , the "monomer M, the "dimer" M2 and the "metal anion" M. Most data suggest that M, M2, and M are simple electrostatic assemblies of ammoniated cations and ammoniated electrons The reaction, e + NH3 - lf 2 H2 + NH2 is reversible, and the directly measured equilibrium constant agrees fairly well with that estimated from other thermodynamic data. Kinetic data for the reaction of ethanol with sodium and for various metal-ammonia-alcohol reductions of aromatic compounds suggest that steady-state concentrations of ammonium ion are established. Ethanol-sodium reaction data allow estimation of an upper limit for the rate constant of e + NH4+ 7, H2 + NH3. 

It was reported that the structure of the product obtained (68% yield) by acid-catalysed (8% HC1, reflux, 18 hr) hydrolysis and decarboxylation of the (3-keto ester 1 was not the expected diketone, but the stable enol 2 (mp 128-130°C), and that the equilibrium could not be reversed from enol to ketone, even on treatment of 2 with dilute alkali for 10 days. The evidence cited in support of 2 was entirely spectroscopic, as follows "C14H16O3 (232) M+ 232, Xmax (ethanol) 266 nm (log e, 4.09). The IR spectrum of 7 (= 2) showed a broad band between 3000-3500 cm 1 (enolic OH) and a sharp peak at 1705 cm-1 (ring -C=0) in the NMR spectrum (CDCI3) of 7 (s 2) a broad peak was present at 85.95 (1H, olefmic) and a downfield signal (exchangeable with D2O) at 811.1 (1H) indicating the presence of an enolic OH group."... 

The equilibrium between 138 and the reversible oxidation product 148 is vital to plant and animal life it apparently functions to mediate the transfer of hydrogen atoms. Solutions of L-ascorbic acid, which is readily oxidized, are more sensitive to alkalies than to acids, and the rates of oxidation are lower under slightly acid conditions. The stability of 138... 

This type of reaction, known as the aldol reaction, which occurs particularly in the presence of alkali, is reversible, resulting in an equilibrium between the proportions of single and combined molecules. 

Reversible Equilibria. As noted in Table I, there are many reversible equilibria available in alkali metal vapors to accomodate external stresses and perturbations. The liquid t vapor equilibrium is of fundamental importance in connection with heat pipes (1) and also in many applications, e.g. lithium in fusion (25). Equilibria involving clustering (beginning with atom-atom recombination to the diatom (3, 4)) are just beginning to be understood quantitatively. Equilibria involving ionization are of major importance for the readily ionized alkali metal species (18, 19, 38). A final equilibrium which has apparently been much less studied (1) is the "Mott" metal-insulator transition which occurs for all alkali metal vapors at high density (52, 53). 

Intercalation reactions of the dichalcogenides with alkali metals are redox reactions in which the host lattice is reduced by electron transfer from the alkali metal. Lithium and sodium intercalation reactions, for example, have been studied using cells of the type Li/LiC104-dioxolane/MX2 andNa/Nal-propylene carbonate/MX2. The reactions proceed spontaneously to form the intercalation compound if the cell is short circuited alternatively, a reverse potential can be apphed to control the composition of the final product. Apart from their application in synthesis, such electrochemical cells can be used to obtain detailed thermodynamic information and to establish phase relations by measuring the dependence of the equilibrium cell voltage on composition (see Figure 4). 

---