New Insights on the Mechanisms of the pH-Independent Reactions of Benzo[a]pyrene 7,8-Diol 9,10-Epoxides
| Autor: | H. Yagi, Dale L. Whalen, Lanxuan Doan, D. M. Jerina, Bin Lin |
|---|---|
| Rok vydání: | 2001 |
| Předmět: |
chemistry.chemical_classification
Base (chemistry) 7 8-Dihydro-7 8-dihydroxybenzo(a)pyrene 9 10-oxide Diol General Chemistry Hydrogen-Ion Concentration Carbocation Biochemistry Medicinal chemistry Catalysis Ion Structure-Activity Relationship chemistry.chemical_compound Hydrolysis Colloid and Surface Chemistry Models Chemical chemistry Yield (chemistry) Hydroxides Pyrene Organic chemistry Hydroxide |
| Zdroj: | Journal of the American Chemical Society. 123:6785-6791 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | The rates and products of the reactions of (+/-)-7beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (1) and (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (2) in water and dioxane-water mixtures have been determined over a pH range wider than that of earlier studies. This study provides additional insight on the mechanisms of the pH-independent reactions of 1 and 2. The rate profile for reaction of 1 shows acid-catalyzed hydrolysis at pH5, a rate plateau at pH 5-9.5, a negative inflection at pH 10-11.5, and a rate increase at pH11.5. The rate decrease between pH 10 and pH 11.5 is accompanied by a decrease in the yield of tetrols from 60% (pH 8) to 29% (pH 11.2) and is interpreted to be the result of a partial change in mechanism brought about by attack of hydroxide ion acting as a base to deprotonate a carbocation intermediate and regenerate 1 at pH10, thus reducing the contribution of the pathway for tetrol formation in which water attacks the carbocation. The rate profile for the reaction of 2 exhibits only a single rate plateau at intermediate pH, along with increases in rate at low and high pH because of second-order reactions of 2 with H+ and HO-, respectively. The lack of a rate depression at pH10 and the product studies for the reaction of 2 in dilute sodium azide solutions suggest that the tetrol-forming reactions of the pH-independent reaction of 2 are concerted or near-concerted. |
| Databáze: | OpenAIRE |
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