Stoichiometry The stoichiometry for oxidation of p-Aminobenzhydrazide / p-Chlorobenzhydrazide by Fe(III) in the presence of PPDTS have been studied. A known excess of Fe(III) was added to a solution containing known amounts of p-Aminobenzhydrazide / p-Chlorobenzhydrazide and PPDTS. The reaction was allowed to go to completion, which is indicated by the constancy of absorbance of the reaction mixture. The amount of Fe(II) formed was computed from the absorbance at 563 nm for Fe(PPDTS)37-. The amount of Fe(II) formed is equal to the amount of Fe(III) reacted. From these values the ratio of the amount of Fe(III) and PABAH/PCBAH reacted has been calculated and the results are tabulated in Table 1.
The results suggest that the stoichiometric ratio, [Fe(III)] : [PABAH] / [PCBAH] is 4 : 1. The overall reaction in the presence of PPDTS may be represented as where X = NH2 or Cl
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The pseudo-first order rate constants increase with increases in [PDTS]. Plots of 1 / kobs versus 1 / [PPDTS]2 are linear with positive slopes and positive intercepts (Figure 2) confirming the formation of 1:2 complex between Fe(III) and PPDTS.
Effect of hydrogen ion
It has been observed that these reactions are decelerated by hydrogen ion. Kinetic runs were performed at different [H+], keeping the concentrations of Fe(III), PPDTS and PABAH / PCBAH constant and the pseudo-first order rate constants were evaluated (Figure 3).
Effect of ionic strength
These reactions were also carried at different µ (0.050 to 0.30 i.e., at 0.050, 0.10, 0.150, 0.20, 0.250 and 0.30), keeping the concentrations of Fe(IIII), [PABAH] / [PCBAH], PPDTS and H+ constant. The data (Table 3.) show that ionic strength has little effect on these reactions.
Determination of protonation constant of PABAH and