ESR Study of Nitroxide Radicals Generated from Triaz-2-en-1-ols

✍ Scribed by Ladislav Omelka; Imrich Vrábel; Katarína Erentová; Jochen Dauth; Bernward Deubzer; Johann Weis

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: German
• Weight: 410 KB
• Volume: 79
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19960790310

✦ Synopsis

The triazenols 4-R1-C6H4-N=N-N(OH)-R2 (l), oxidized with t-BuO; radicals, produced nitroxide radicals R'-C6H4-N(O')-N=N(R2)+0-

(5). The suggested radical structure was confirmed by "N-labeling. The reaction of triazenols 1 with PbO, proceeded under N2 elimination, in which case nitroxides R'-C6H4-N(R2)-O' (2) were observed as the final radical products. The intermediate R'-C& radicals were identified by spin-trapping.

Introduction

. -Although nitroxides represent one of the most intensively studied radical groups [l], only a few ESR data are reported on the radicals with the N-0' function situated on a triazene skeleton. This fact can be explained by the marked tendency towards N, elimination accompanying the attempts to prepare them from triazenes as starting compounds. Earlier ESR studies have shown [2] [3] that the oxidation oftriazenols4-RI-C6H,-N=N-N(0H)-R2 (1; R' = H, NO,; R2 = t-Bu, Ph) withagents like alkaline K,[Fe(CN),] or PbO, leads to the nitroxides 4-Rl-C,H,-N(R2)-0'

(2). Re-

cently, a similar behavior was also confirmed for triazenes 4-R1-C,H,-N=N-NH-R', in which case radicals 2 were observed on oxidation with 4-nitrobenzenecarboperoxoic acid, and alkoxy aryl nitroxides 4-R'-C6H,-N(O')-O(t-Bu) were detected by the oxidation with t-BuO; radicals [4]. As more efficient method for the preparation of triazenoxy radicals, the spin-trapping reaction of nitroso compounds with photolytically generated N-radicals was found [5] [6].

Within the framework of this paper, we have aimed at a generation of triazenoxy radicals from a series of triaz-2-en-1-01s 1 with the system t-BuOOH/PbO,, effectively