The cobalt( i i i ) chelates of ethylenediaminetetra-acetic acid, iminodiacetic acid, NN'-bis-(2-aminoethy1)ethylenediaminehexa-acetic acid, and A/'-hydroxyethylenediamine-A/"'-triacetic acid have been prepared and analysed.and the stability constants measured over a pH range. Reproducible redox potentials were obtained by use of a gold-plated, gold indicator electrode in conjunction with a pH meter. The relative values of the stability constants were in agreement with those expected from the chemical structures of the chelates.

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The stability constants of the ferrous and ferric chelates of ethylenediamine-tetra-acetic acid, methylethylenediamine-tetra-acetic acid, cyclohexane diamine-tetra-acetic acid and djethylenetriamhe-penta-acetic acid have been determined. Redox potential measuremeiits on the " ferrous-ferric-chelating agent " system were carried out and the pH dependence of the redox potential measured. From these results and a direct potentiometric determination of the ferrous-chelate stability constant, that of the ferric-chelate was calculated. Suggestions have been made to account for the difference in the stability of the various chelates.Addition of a complexing agent to a redox system is likely to alter the value of the redox potential, the relative strengths of the binding of the ligand to the oxidized or reduced state of the metal determining, in part, whether it is the oxidizing or reducing power of the couple which is enhanced. A well-kncwn example of the reduction of the redox potential on complexing iron is furnished by the ferrocyanide + ferricyanide system, in which the potential is 0.36 V 1 as compared to that of 0,749 V 2 for the uncomplexed ferrous + ferric couple at 25°C. Schwarzenbach 3 and Belcher et al.4 have found, and we have confirmed, that this latter redox potential is reduced, between pH 3.5 and 6-5, to 0.117 V on the addition of ethylenediamine-tetra-acetic acid (EDTA).The stability constant of the ferric chelate of EDTA is the "concentration equilibrium constant " of the reaction, where Y4-represents the fully ionized EDTA :(1)Similarly, Kpeyz-, the stability constant of the ferrous chelate is given byThe formal redox potential of the process, is given bySimilarly, the redox potential of the process, FeY2-+ Fey-+ e is given by 2.303 RT [Fey-] Echelate = E'chelate + 7 log10 * These two potentials are equal at equilibrium and thus the equation,can be obtained from a combination of eqn. (l), (2), (3) and (4). Hence, by determining the standard redox potentials of the ferrous + ferric system both in the absence and presence of chelating agent, the difference between the logarithms of the stability constants of the ferric and ferrous chelates can be calculated.

SynopsisThe reaction of hydrazine hydrate with manganic hydroxide and its application to the solution polymerization of methyl methacrylate has been studied. The kinetic evidence suggests that the hydrazine and the monomer are both adsorbed on the surface of the manganic hydroxide sol and that the decomposition of the hydrazine and the polymerization of the methyl methacrylate follow zero-order kinetics. The rate of polymerization increases slowly with increasing temperature, the activation energy for the polymerization being 4.9 f 0.2 kcal/mole.

SynopsisThe cupric sulfate-hydrazine system has been used to initiate the aqueous solution polymerization of methyl methacrylate a t pH 9.25 in the presence of oxygen. At cupric sulfate concentrations greater than the saturation solubility of cupric hydroxide, hydraeine is adsorbed on, and decomposes on, the surface of the hydroxide. The kinetics of the decomposition are zero-order both in the absence and the presence of monomer. The initiation of the polymerization occurs both at the surface of the cupric hydroxide onto which some monomer is adsorbed and also in solution. Below the saturation solubility of cupric hydroxide, the initiation reaction between cupric ions and hydrazine occurs in solution. EXPERIMENTAL Preparation and Purification of MaterialsStabilized methyl methacrylate was distilled under reduced pressure in an atmosphere of nitrogen and used immediately. * Present address: Headmistress, Westholme School, Blackburn, Lancashire, England. tFormerly the Royal College of Advanced Technology. 379Methyl Methacrylate.