Short communicationIdentification of 2,3-butanedione monoxime hydrogenation products by gas chromatography–mass spectrometry in an ion trap mass spectrometer
Introduction
The reduction of α-hydroxyimine carbonyl compounds is one of the most important methods for the synthesis of 2,3,5,6-tetrasubstituted and 2,5-disubstituted pyrazines [1]. We recently studied the preparation of 2,3,5,6-tetramethylpyrazine (TMP), which has been widely used in the treatment of patients with cerebral ischemic diseases in China [2], via reduction of 2,3-butanedione monoxime (BDM) with hydrogen in the presence of homogeneous catalyst [3].
Besides TMP, other products with a nitrogen-containing heterocyclic ring appear to be present in the reaction. Although the reaction has been researched, relatively few studies of the identification of the reaction products apart from TMP have been reported, due to their smaller amounts and difficulty of isolation. The identification of these products and intermediate products is required for TMP used as a medicine material, a study on the mechanism of the reaction is also important. The combination of quadrupole ion trap mass spectrometry interfaced with gas chromatography (GC–MS) is now becoming widely available with its high sensitivity, high specificity and the relatively low cost of instrument [4]. Thus the GC–MS method can be widely used in the studies on more reaction products and the mechanisms of their formation. The basic objective of the present work was to identify the principal BDM hydrogenation products.
Section snippets
Sample
The catalytic hydrogenation of BDM in ethanol solution of 0.2 M initial concentration was carried out in a 24-ml glass-lined stainless steel autoclave at 80 to 150°C under H2 pressure of 0.6∼2.4 MPa for 1–6 h. A mixture of homogeneous transition metal catalyst [3] and BDM (0.1 mmol) in ethanol (5 ml) was added to the autoclave. The reactor was purged five times with hydrogen, before setting the required H2 pressure. Hydrogen up to the required H2 pressure was introduced and the reaction vessel
Results and discussion
Fig. 2 shows a typical total ion chromatogram of a 0.2 M BDM solution after hydrogenation. Apart from the BDM peak (peak 1), various other peaks representing hydrogenation and condensation products are evident.
Peaks 2–7 and peak 9 were found to be tetramethylpyrazine (TMP), 2,4-dimethyl-3-ethylpyrrole (DEPR), 3,4,5-trimethylpyrazole (TPZ), 2,5-dimethyl-1-propylpyrrole (DPPR), 3-acetyl-2,4-dimethypyrrole (ADPR), 3,5-dimethyl-4-allylpyazole (DAPZ), and 2,2′-bipyridine (BPY), respectively, by
Acknowledgements
The financial support provided for this work by the Zhejiang Education Committee is gratefully acknowledged.
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