Kinetics and mechanism of bromination of styrenes
| Autor: | Keith Yates, W. V. Wright |
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| Rok vydání: | 1967 |
| Předmět: | |
| Zdroj: | Canadian Journal of Chemistry. 45:167-173 |
| ISSN: | 1480-3291 0008-4042 |
| DOI: | 10.1139/v67-033 |
| Popis: | The kinetics of bromination of six substituted styrènes (3-fluoro-, 3-chloro-, 3-bromo-, 3,4-dichloro-, 3-nitro-, and 4-nitro-) in anhydrous acetic acid have been investigated at several temperatures. At 25.3 °C the reactions follow the rate expression [Formula: see text]The rate constants for the second order process show a good linear free energy relationship of the log k versus σ type with ρ = − 2.24. (The value obtained at 35.3 °C is − 1.93.) No simple rate-substituent dependence is obtained for the more complex third order process. Activation parameters have been obtained for the second order brominations, the ΔS≠ values being large and negative. Bromination of styrene in the presence of a large excess of acetate or nitrate gives only two products in each case, the α,β-dibromide and the α –acetoxy β-bromide or α -nitrato- β -bromide respectively.The magnitude of the reaction constant ρ, the values of ΔS≠, and the reaction products all support a mechanism involving a highly unsymmetrical bromonium ion intermediate. |
| Databáze: | OpenAIRE |
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