Protolytic equilibrium of certain annelated azoloazines |
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Authors: | A P Volovodenko R E Trifonov P V Plekhanov G L Rusinov D G Bresnev V A Ostrovskii |
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Institution: | (1) St. Petersburg State Technological Institute, 198013 St Petersburg, Russia;(2) Institute of Organic Synthesis, Urals Branch, Russian Academy of Sciences (RAN), 620219 Ekaterinburg, Russia |
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Abstract: | The first and second protonations of annelated azoloazines have been investigated quantitatively in aqueous solution. Compounds investigated were pyrazolo1,5-a]pyrimidine (pKBH
– 0.03±0.02, pKBH
2+ –7.87±0.30), 1,2,4-triazolo4,3-b]-1,2,4-triazine (pKBH
+ –0.04±0.02, pKBH
2+ –8.00±0.10), 1,2,4-triazolo1,5-a]pyrimidine (pKBH
+ 0.21±0.03, pKBH
2+ –9.00±0.09) and its 6R derivatives (R=NO2, Br, Cl). The annelated azoloazines studied are weaker bases than their unannelated analogs. According to quantum chemical calculations (AM1), protonation of these heterocycles may occur both at the azole and the azine fragments of the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 816–824, June, 2000. |
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Keywords: | annelated azoloazines basicity protonation prototropic tautomerism |
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