Experimental evidence of formation of imines in the course of reduction of hydrazones |
| |
Authors: | MS Baymak H Celik H Lund P Zuman |
| |
Affiliation: | 1. Department of Chemistry, Clarkson University, Potsdam, 8 Clarkson Avenue, NY 13699-5810, USA;2. Department of Organic Chemistry, Aarhus University, Aarhus, DK, Denmark |
| |
Abstract: | The reduction of hydrazones is generally suggested to proceed through a reductive cleavage of the nitrogen–nitrogen bond followed by a reduction of the carbon–nitrogen bond. This sequence of reduction processes is here supported for fluorenone (V) and benzophenone (VI) hydrazones as well as by a comparison of the reduction of fluorenone and benzophenone hydrazonium ions (I,III) with corresponding imines (II,IV). Another proof of the presence of imines as intermediates is the splitting of four-electron waves of hydrazones V and VI and hydrazonium ions I and VIII into two waves at pH < 2. This has been interpreted as due to differences in slopes dE1/2/dpH and pKa-values of protonated hydrazine derivatives on one side and corresponding imines on the other. In this pH-range imines formed in reductions of VI and VIII are reduced in a single two-electron wave, those of I and V in two one-electron steps. Fluorenone imine (II) is sufficiently stable to allow recording of time-independent current–voltage curves between pH 6 and 11. In this pH-range the imine (II) is reduced in two one-electron steps. Benzophenone imine (IV) has been found stable between pH 4.6 and 12. At pH 4.6–8 the reduction of the imine IV takes place in a single two-electron step, at pH 8–12 in two one-electron steps. Final proof of the initial cleavage of the N–N bond is presented by comparison with the reduction of nitrones. |
| |
Keywords: | Hydrazones Imines Electroreduction Reactive intermediate Polarography |
本文献已被 ScienceDirect 等数据库收录! |
|