Reaction of Azodioxide with Thianthrene Cation Radical

Abstract

We recently reported on the thianthrene cation radical perchlorate (Th·ClO4) induced oxidative decomposition of carbonates (eq 1), carbamates (eq 2), azodicarboxylate (eq 3), dicarbonate (eq 4), peroxides (eq 5), and disulfide (eq 6) where R in equations is tert-butyl. In each of these reactions, electron-transfer-mediated C,N, C,O or C,S bond cleavage was found. Substantial bond weakening was shown to accompany the tert-butyl cation due to the electron loss from these substrates. In a continuation of our work on N,N'-dioxoazobis(2methyl-2-propane) (1) in acetonitrile solution at room temperature, C,N and N,O cleavages, followed by addition of Th·ClO4 to azodioxide, 1, was found to give thianthrene oxide (ThO) and N-t-butylacetamide (3), with evolution of nitrogen gas. Reactions of Th·ClO4 with anions, such as nitrite and nitrate ions, have been reported, but its reactions with molecules with an abnormal number of bonds have not been documented. This work affords the first example of the addition of a cation radical to formal negatively charged oxygen within a neutral molecule. Reactions of nitrite and nitrate ions with Th·ClO4 were found to give thianthrene 5-oxide (ThO) quantitatively (Scheme 1). Reactions with O-labeled nitrite and nitrate ions showed that the oxygen in ThO came from the nitrite and nitrate ions respectively. In the present study, as with the other oxidative decomposition, the major products from the reaction of 1 with Th·ClO4 are also characteristic of tert-butyl cations, which imply carbocationic chemistry is predominantly observed from a nitrosoalkane dimer. The products obtained were N-tbutylacetamide (3), ThO and N2 as determined by quantitative GC and GC/MS analyses. N-t-butylacetamide (3) from the tert-butyl cation, which was isolated in a yield of 91%, and ThO (76%) was obtained by oxygen transfer from 1. Without doubt, 3 arose from hydration, during workup, of a Ritter-type intermediate (Me3CN=CMe) from the reaction of Me3C with the MeCN solvent. Accordingly, all reactions were carried out with a 2:1 stoichiometry of the cation radical and 1. Generally, in the reaction of thianthrene cation radical perchlorate, ThO is obtained as a side product from the hydrolysis of Th·ClO4 by water, either adventitiously in the solvent or added during workup. However, in this