Kinetic and Mechanism of Oxidation of Methylaminopyrazole Formamidine by Alkaline Hexacyanoferrate(III) and the Effect of Divalent Transition Metal Ions

Ahmed Fawzy

doi:10.11648/j.sjc.20160401.11

Abstract

In aqueous alkaline medium, the kinetics of oxidation of methylaminopyrazole formamidine (MAPF) by hexacyanoferrate(III) (HCF)has been studied spectrophotometrically under the conditions, MAPF >> HCF at a constant ionic strength of 0.1 mol dm-3 and at 25°C. The reaction showed first order dependence on [HCF] while it exhibited fractional-first order kinetics with respect to [MAPF] and [OH-]. The oxidation rate increased with increasing ionic strength and dielectric constant of the reaction medium. Addition of small amounts of some divalent transition metal ions accelerates the oxidation rate and the order of catalytic efficiency was: Cu(II) > Ni(II) > Zn(II) > Co(II) > Cd(II). The suggested mechanism involves formation of a 1: 1 intermediate complex between HCF and the deprotonated MAPF species in a pre-equilibrium step. The final oxidation products were identified as methylaminopyrazole, dimethylamine and carbon dioxide. The appropriate rate law was deduced. The reaction constants involved in the mechanism were evaluated. The activation and thermodynamic parameters were determined and discussed.

Highlights

Oxidation reactions are very important in nature and are regarded as key transformations in organic synthesis
Oxidation of organic compounds by hexacyanoferrate(III) as an efficient one-electron oxidant has been a subject of much interest especially in alkaline media [6,7,8,9,10,11,12,13,14,15,16,17]
The stoichiometry was determined spectrophotometrically which indicates the consumption of two HCF ions for one molecule of methylaminopyrazole formamidine (MAPF) to yield the oxidation products as shown in the following equation, The above stoichiometric equation is consistent with the results of product identification which carried out by spectral and elemental analysis as described elsewhere [22,23,24]

Summary

Introduction

Oxidation reactions are very important in nature and are regarded as key transformations in organic synthesis. During the last few decades formamidines have achieved commendable importance due to their very broad spectrum of biological activity [1, 2]. The N, N-dialkyl derivatives of formamidines are highly effective acaricides and the most rewarding of these studies resulted in discovery of the acaricide insecticide chlordimeform [3, 4]. The oxidative cleavage of formamidines is quite important, since the N, Ndialkyl formamidine group is one of the most versatile protecting groups, especially in biosynthetic applications. It adds less error to the experimental results, and data can be analyzed meticulously to establish the reaction path

Results

Discussion

Conclusion