The reaction between oxygen and sulphite in the presence of cobalt(1r) as catalyst has been studied at the low concentrations which are of interest in relation to water treatment processes employed in the ' waterflood ' secondary oil-recovery technique. A continuous-flow apparatus was used to study reaction times of 0.1-1.7 s using iodine titration of the sulphite to follow the reaction, and initial concentrations of sulphite 0.35-1.13 mmol dmP3, oxygen 0.029-0.22 mmol dm-3 and cobalt 0.20-25.3 pmol drnp3. A static method was used to measure sulphite as a function of time at lower concentrations, using the fuschin-formaldehyde method. Reaction times were 2-60 min, with initial concentrations of sulphite 10-62, oxygen 3.422 and cobalt 0.01-0.05 pmol dmP3.In both concentration ranges the reaction showed an induction period during which little or no reaction occurred, followed by an almost linear decay in sulphite concentration. The orders of reaction with respect to sulphite and oxygen were 1.5 and 0 over the whole concentration range studied. However, the order with respect to cobalt increased from 0.5 to 1.5 on moving to the lower concentrations, and a general rate equation is developed to express the experimental rate behaviour :The activation energy in the low-concentration range was found to be 183 kJ mol-l. Added hydroquinone inhibited the reaction strongly and a chain mechanism is proposed involving reaction via a series of cobalt complex intermediates.

Kinetic aspects of the sulfite-oxygen reaction have been studied at very low concentrations (ca. 50 and 11 µ dm™3 of S032™ and 02, respectively). Neither sodium sulfite nor ammonium bisulfite reacts appreciably in the absence of a catalyst. In the presence of cobalt(II) (19-48 nmol dm™3), the ammonium salt reacts ca. 2.5 times more slowly than the sodium salt. The strong variation of rate with pH was an interesting and unexplained effect. Natural seawater was found to exhibit variable but substantial catalytic activity. Studies in synthetic seawater showed that (in order of reactivity) Co(II) > Cu(II) » Ce(IV) > Mn(II) were active catalysts, while Ni(II), Fe(II), and Fe (III) were inactive. The effect on rate of the high ionic strength of seawater was semiquantitatively consistent with the Bronsted-Bjerrum theory.

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.

The polyaminocarboxylic acids, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), cyclohexanediaminetetraacetic acid (CDTA), and diethylenetriaminepentaacetic acid (DTPA) have been used to chelate the cupric ion when the system cupric ion—hydrogen peroxide is used as an initiator for the emulsion polymerization of styrene. The same maximum zero order rate of polymerization of approximately 60% conversion/hr. is obtained in all cases, although with NTA this occurs from pH 3–6 while with EDTA, CDTA, and DTPA the maximum occurs in the regions pH 4–7, pH 3–7, and pH 6.5–9.5, respectively.

SynopsisThe use of cobalt(I1) complexed with various polyaminocarboxylic acids and hydrogen peroxide has been shown to be an effective initiator for the emulsion polymerization of styrene. The polyaminocarboxylic acids used were ethylenediaminetetraacetic acid (EDTA), ammonia diacetic acid (ADA), N,N'-bis(2-aminoethyl)ethylenediaminehexaacetic acid (TTHA), ammonia triacetic acid (ATA), and N'-hydroxyethylethylenediamine-N,N,N'-triacetic acid (HEEDTA). In the case of the HEEDTA system, the effect of varying the concentrations of the initiator components was examined and found to be broadly similar to that observed in other metal ion chelate-hydrogen peroxide initiators. All the systems were effective over a wide pH range (generally 3-9), and zero-order rates in the range of 30-9O'%/hr were observed, although there was considerable variation in detail in the manner in which the zero-order rate depended on pH. The behavior of these systems is commented upon in the light of earlier results on similar systems and of previously published redox potentials of the related cobalt(I1)-cobalt(II1) chelate systems.