KINETIC METHODS AND KINETICS OF THE OXIDATION OF WATER, NITRILOTRIACETIC ACID, AND RELATED ORGANIC SUBSTANCES BY POTASSIUM FERRATE

The rate constants and values for absorbance at time t = 0 can be calculated with great speed, simplicity, and accuracy using the mathematical treatments presented herein. The fundamental assumption that, given a proposed kinetic model, the sum of the absorbances is directly related to the sum of the rate constants for the reaction is shown to be valid, leading to a one-pass process for calculation of rate constants. It was found that many factors can effect the observed rate constants of the oxidation of organic substrates by the ferrate (VI) ion. Selection of buffer will either increase or decrease or decrease the observed rate constants, depending upon the buffer chosen. Increasing the total ionic strength will increase the observed rate constants, while the effect of changing the initial potassium ferrate concentration is not altogether clear. The presence of Fe(III) generated from the reduction of Fe(VI) in solution enhances the rate of oxidation, while adding Fe(III) to the unreacted solution does not affect the oxidation rate. Dual-wavelength spectroscopy was used to try and eliminate any effect in the calculated rate constants due to absorption or scattering of light by the Fe(III) product. It was found that the results were identical to those found when using a single wavelength, dual beam spectrophotometer. The kinetics of the oxidation of water by ferrate (VI) were examined in the pH range of 4.80 to 7.78. The kinetic data were processed on-line as received from a stopped-flow spectrophotometer. The data were shown to fit a mixed-order kinetic model. The second-order process was by far the largest contribution to the rate. As a result, the second-order rate constants showed a much clearer trend than the corresponding first-order rate constants. The reactions showed a strong pH dependence. The half-lives of the reactions ranged from about 100 msec at pH 4.80 to about 50 sec at pH 7.78. The results from the higher pH range (7.5 and above) were in good agreement with those obtained by other workers. The kinetics and the products of the reaction of nitrilotriacetic acid and ferrate (VI) were examined. The possible oxidation products had kinetic data which displayed good fit to a pseudo-first order model and showed rates of reaction related to the ability of the ferrate ion to attack the nitrogen-carbon bonds of the substrates. As a result, the rates of oxidation of tertiary amino-carboxylates (NTA, MIDA, DMG) were found to be about 50 times slower than those of the primary and secondary amino-carboxylates (GLY, SARC, IDA). The products of the oxidation of NTA by the ferrate (VI) ion where examined by a variety of techniques. It was found that the oxidation of NTA involves successive cleavages at the amino nitrogen-carbon bond to form IDA, GLY, and ammonia. IDA was found to accumulate as was predicted by the rate law ans observed rate constants. The investigation of the kinetics of 2-carbon 2 functional group systems is still underway. The kinetic data seem to show good fit to a pseudo-first-order kinetic model. It appears that the presence of aldehyde functional groups greatly enhance the rate of reaction, while the presence of alcohol or carboxylic acid groups reduce the rate of reaction. As such, it was found that glyoxal and glyoxylic acid react quickly, ethylene glycol, exalic acid, and glycolic acid react slowly, and glycol aldehyde is somewhere in between. The products of the reactions of the 2-carbon substrates with the ferrate ion are currently being investigated by G.C. and G.C./M.S. Preliminary results show that at least 4 of the 6 substrates can be separated by G.C. using the TMS derivatives of the substrates