Identification of 2-chloropyrazine oxidation products and several derivatives by multinuclear magnetic resonance

Abstract

1H, 13C, 14N and 15N NMR chemical shifts were used to prove the structures of the products of 2-chloropyrazine oxidation. It was shown that oxidation by hydrogen peroxide in acetic acid or m-chloroperbenzoic acid leads to the N4-oxide, whereas potassium persulfate in sulfuric acid gives the N1-oxide as the main product. Additionally, the results of NMR measurements of products from the nucleophilic substitution of the chlorine atom by azide anion, yielding the respective azides, and ethylation reactions of both 2-chloropyrazine N-oxides leading to the N-ethyl salts confirm the structures of both isomeric N-oxides. Protonation studies of the compounds obtained are also reported. The favoured protonation site is found to be the N atom that is not hindered by any substituents, and in some cases probably the oxygen atom of the N-oxide function. Copyright © 2003 John Wiley & Sons, Ltd.