Dinitrogen tetroxide characterization

Furazan 1 was first prepared and characterized in 1964 by melting glyoxime 2 with succinic anhydride in 57% yield (64JA1863, 65JOC1854). Its A-oxide, furoxan 3, has been in a focus of attention for chemists for more than a century, but was synthesized only in 1994 by oxidation of 2 with dinitrogen tetroxide in dichloromethane in 45% yield (94MC7) (Scheme 1). The A-oxide cannot be prepared by direct oxidation of furazan. 

The primary addition product from HFA and diphenylphosphane (32b) has been unambiguously characterized by several groups (97, 755). It is easily oxidized by atmospheric oxygen and dinitrogen tetroxide (97, 755) to form phosphonous acid ester 33b via phosphane oxide 36 (755), which can also be synthesized from HFA and diphenylphosphane oxide. Kinetics of the base-catalyzed rearrangement have been studied (754). Further action of HFA on 32b yields difluorophosphorane 37 (755). A dipolar intermediate with tetra-coordinated phosphorus has been postulated by Stockel (260) in the formation of 33b and 33c (R = c-CgHu). 

In the remaining section nitration (21) by dinitrogen tetroxide in dry carbon tetrachloride solution is considered. Typical data are shown in Table II. There appear to be two distinct types of reaction with toluene. The first is apparent at low concentrations of N2O1, (< about 0.2 mole 1 ) where product isomer distributions characterized by a high percentage of m-nitrotoluene were observed. At high N2O1, concentrations A similar phenomenon occurs with -methylanisole (23) and also p-chloroanisole (20) on nitration in acetic anhydride. 

A number of triatomic radicals can form dimers whose geometries have been well-characterized. A study of the electronic structures of these dimers can illustrate aspects of qualitative valence-bond and molecular orbital theory for electron-rich polyatomic molecules, and interconnections between these theories can be demonstrated. Dinitrogen tetroxide is a molecule par excellence that may be used for these purposes, and here we shall give primary consideration to its electronic structure and bond properties. 

---