Cobalt equilibrium shift

I might suggest some preliminary studies just to see what the colors are as the equilibrium shifts in the different directions. To do this, I would suggest preparing a solution of cobalt nitrate, perhaps 0.4 M, and then adding chloride ions either by dropwise addition of concentrated HC1, or by adding crystals of NaCl. You should see the shift from pink to blue. 

The tautomerization is induced by cobalt(II) which forms the thermodynamically more stable metalatcd hydroporphyrins from which the cobalt can be removed using trifluoroacctic acid under kinetic control. Experiments with porphyrinogen and hexahydroporphyrin show that the porphyrinogen-hexahydroporphyrin equilibrium can be shifted by complexation of porphyrinogen with metal ions to the more stable metal hexahydroporphyrins and that metal-free hexahydroporphyrins tautomerize back to the more stable metal-free porphyrinogens.29... 

The cis/trans isomerization reaction, Eq. (24), has been applied in the preparation of salts of the cis isomers of the chromium(III) complexes with L3 = (NH3)3 or tacn (319). For these species Eq. (24) equilibrium is shifted to the right, while the corresponding equilibria with the diaqua or dihydroxo species, respectively, are shifted to the left (Table X). The increased stability of the cis aqua hydroxo species can be explained in terms of intramolecular hydrogen bond formations (Section VI,C). As mentioned above, the corresponding cobalt(III) and rhodium(III) complexes have been isolated as salts only in the case of the trans-(H20)L3M(0H)2ML3(H20)4+ cations, but it seems very probable that their cis isomers could be prepared by reaction Eq. (24). 

Ealy, Jr., "Effect of Temperature Change on Equilibrium Cobalt Complex" Chemical Demonstrations, A Sourcebook for Teachers, Vol. 1 (American Chemical Society, Washington, DC, 1988), p. 60-61. Concentrated hydrochloric acid is added to pink [Co(H20)5]2+ until blue [C0CI4]2- is formed. When heated the solution turns darker blue when cooled the solution turns pink, indicating that the reaction is endothermic. Students are asked to examine the equilibrium reaction and predict how the system will shift upon the addition of water. 

An equilibrium mixture of CO 2 and HCOJ at a total concentration sufficient to produce a mixture of enzyme-substrate complexes did not reveal any new spectral species of the Co(II) enzyme (48,41). The spectral change was shifted to higher pH, however, and this was taken to imply a preferential binding of HCOi to the acidic enzyme form with little effect on the cobalt spectrum. Whether this complex represents an active intermediate can not be resolved at present. 

Here, nickel is extracted with a di(2-ethylhexyl) phosphoric acid in its H-form (HDEHP) and two protons are set free. This causes a pH-shift during extraction, which can be avoided if the ion exchanger is, for example, in the Na-form. Typical extraction isotherms are depicted in Fig. 10.2. At the indicated pH-value no nickel, but more than 80 % cobalt, can be extracted in one equilibrium stage. During cobalt... 

On the other hand, H2S did not prevent cis-trans isomerization and double bond shift reactions from going to completion at 300° or 350°, and the olefin mixtures analyzed were always found to be close to thermodynamic equilibrium, whether they had been formed from thiophene, butadiene, or one of the olefins themselves. Nor did H2S prevent the total conversion of butadiene to butene, even when 10- to 20-cc. samples were used at reaction temperatures down to 200° C. and flow rates up to 10 liters per hour. This may be the explanation of the absence of butadiene from the thiophene reaction products over cobalt molybdate—that if it had been formed as it was over chromia, it would have reacted further too rapidly to survive. 

A high CO pressure would shift equilibrium (4.3) to the left and the catalytic reaction would become slower. In this complex CO is a far better ligand than an alkene. On the other hand the reaction uses CO as a substrate, so it cannot be omitted. Furthermore, low pressures of CO may lead to decomposition of the cobalt carbonyl complexes to metallic cobalt and CO, which is also undesirable. Finally, the product alcohol may stabilize divalent cobalt species which are not active as a catalyst ... 

If the amounts of the catalyst ingredients (cobalt, phosphine, and base) are increased by the same factor without change in pressure and H2-to-CO ratio, the increase in phosphine concentration uncompensated by an increase in CO pressure shifts ligand exchange equilibrium toward HCo(CO)3Ph. Without base, this shift is at the expense of the more active HCo(CO)4, producing an apparent reaction order lower than one in "catalyst." In the presence of base, the shift is mostly at the expense of the inactive Co(CO)4, resulting in an apparent order higher than one. 

At lower temperature the equilibrium is shifted in favor of the allophanate but the rate of equilibrium decreases and at room temperature no reaction occurs in 2 weeks. Metal carboxylates (naphthenates, 2-ethylhexanoates, linoresinates of Pb, Co, Cu, Mn, Fe, Cd, V, Zn) were found to accelerate this reaction very appreciably. Particularly active are the lead and cobalt salts which caused complete conversion at room temperature in a few hours. All the metal salts with the exception of the zinc salts also catalyze the... 

May I also suggest one final test Since there is some effect of temperature, perhaps you can take the Co(N03)2 solution to which has been added some 12 M HC1 (about a 5 3 ratio of cobalt solution and the HC1) and split it into three separate test tubes. Heat one test tube in a hot water bath and cool another in an ice bath. This should result in a visible shift in equilibrium and, therefore, pink/blue color changes. From these observations, you should be able to tell which reaction (forward or reverse) is favored by more heat. 

The first step will provide a large volume of uniform experimental material for the students. This step will utilize concentrated HCI, so it should be performed by the instructor while the students watch. The instructor should wear gloves. Concentrated HCI should be slowly added to the cobalt(ll) chloride solution until the entire solution changes color. Students should note the color before and after the change takes place. This should be a change from pink to blue because the equilibrium reaction under study has shifted to the right to partially offset the impact of added chloride ion. A sufficient volume should be prepared to provide every student or team of students with an aliquot of 10 mL of this blue solution. 

Iron catalysts show a tendency to convert the oxygen of carbon monoxide to carbon dioxide, while under. similar conditions cobalt produces water. In all cases long contact times of the reacting products on the catalyst surface increase the carbon dioxide formation and short contact times increase the formation of water. These results (confirmed by experiments with many different catalysts) were the basis for the hypothesis that water is a primary reaction product while carbon dioxide is a secondary product produced by the water gas shift reaction according to equilibrium conditions. 

The second reaction that H2O affects is the equilibrium between metal(ll) and Br ions [27]. At H2O concentrations greater than 5wt%, approximately 12% of total bromide is coordinated to cobalt and only approximately 6% is coordinated to Mn at room temperature. Thus, the metal-bromide equilibria in Figure 4.6 are now all shifted toward Co(OAc)2-4H20. It has been suggested that the bromide is still ion-paired to the metal ion, which makes the reaction between metal(lll) and bromide more difficult in comparison to the case of lower H2O concentration in... 

The use of additives that are capable of coordinating both cobalt(II) and (III) derivatives represents an alternative means of tuning the Co-C bond strength [24]. As depicted in Equation 4.2, the Co"-L species, which results from the decomposition of P-Co "-l, can undergo a second complexation (Co"-b2), which tends to shift the first equilibrium toward the active species (P°). As an illustration, a higher polymerization rate is observed for the VAc polymerization at 30 °C, when adding water molecules that coordinate the cobalt complex [41]. In the presence of water, the PVAc recovered at 70% monomer conversion was still well-defined (M /Mn = 1.12). Such a ligand effect, as reported for the first time... 

Changes in concentrations or partial pressures shift equilibria without changing the value of the equihbrium constant. In contrast, almost every equilibrium constant changes as the temperature changes. For example, consider the equihbrium established when cobalt(II) chloride (C0CI2) is dissolved in hydrochloric acid, HCl(aq), in the endothermic reaction... 

The template synthesis of macrocyclic complexes rra 5-[M(L9)]" (M"" = Ni, Co +, Fe +) from 1-phenyl-1,2-propanedione and 1,3-diaminopropane occurs [44] according to Scheme 1-2. Reaction (1) represents the organic reaction prior to addition of a metal salt. When a methanolic solution of the latter is added to the reaction mixture, the metal-directed condensation is realised, producing the carbi-nolamine and final products. It is obvious that reaction (2) is a consequence of shifting the position of tautomeric equilibrium under the influence of a metal ion exclusively towards [M(L9)] , the latter subsequently being transformed into [M(L10)]"+. That the condensation reaction actually takes place within the metal coordination sphere has been demonstrated by the isolation of the corresponding cobalt(III) macrocyclic complexes with L9. 

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