Кинетика и механизм реакции SNAr замещения N-(2,4-динитрофенил)- 4 диметиламинопиридиниевой соли с пиперидином в ацетонитриле
Електронний архів E-archive DonNTU – (Electronic archive Donetsk National Technical University)
Переглянути архів Інформація| Поле | Співвідношення | |
| Title |
Кинетика и механизм реакции SNAr замещения N-(2,4-динитрофенил)- 4 диметиламинопиридиниевой соли с пиперидином в ацетонитриле
KINETICS AND SNAr SUBSTITUTION MECHANISM IN THE REACTION OF N-(2, 4 -DINITROPHENYL)-4-DIMETHYLAMINOPYRIDINIUM SALT WITH PIPERIDINE IN ACETONITRILE |
|
| Creator |
Тицкий, Г.Д.
Митченко, Е.С. Гайдаш, Т.С. |
|
| Subject |
SNAr механизм
N-арилпиридиниевая соль σ-аддукты кинетика равновесие SNAr mechanism N-arylpyridinium salt σ - adduct kinetics equilibrium |
|
| Description |
Kinetics of the reaction between N-(2,4-dinitrophenyl)-4-dimethylpyridinium tetraphenylborate (I) and piperidine (II) was studied in acetonitrile at 298K in wide amine concentration interval (0.05-2 mol•l-1). Reaction proceeds according to SNAr substitution mechanism at carbon atom of benzene ring and is not accompanied by side processes such as recyclization or SNANRORC. Tetraphenylborate salt (I) was chosen for reaction mechanism study to avoid specific base anion assistance which had been previously revealed for N-arylpyridinium salt with halogen anion. Taking into account dissociation constant of N-(2,4-dinitrophenyl)–4-dimethylpyridinium salt and its low concentration (4•10-5 mol•l-1) we assume that reactive particle in this reaction is cation of salt substrate (Scat). Kinetic control was carried out with spectrophotometric methods on accumulation of reaction product - N-piperidyl-2,4-dinitroaniline (λ=380 nm), as well as on accumulation and decay of intermediates (λ = 515 nm): zwitterionic and anionic σ -adducts (Meisenheimer complexes). Expected catalysis of piperidine was not revealed. Step by step analysis of reaction mechanism was carried out. Rate and equilibrium constants of separate stages have been obtained. It was proved that detected σ-adducts lie on reaction coordinate. Formation of σ-adducts proceeds via molecular complex (MC) N-arylpyridinium salt – piperidine. Critical amine concentration value (b), which defines the rate-determining stage was detected: at b≤ 0.6 rate determining stage is formation of zwitterionic σ1`-adduct, while the concentration of amine increases b≥ 0.6, rate determining stage becomes the decay of anionic σ``2 adduct (Meisenheimer complex). Проведен постадийный анализ механизма нуклеофильного ароматичного замещения для реакции N-(2,4- динитрофенил)-4-диметиламинопиридиний тетрафенилбората с пиперидином в ацетонитриле при 298К. Спектрофотометрическим методом зафиксировано образование σ -аддуктов. Кинетический анализ, проведенный в широком интервале концентраций амина, показал, что образующиеся σ -аддукты лежат на координате реакции, а им предшествует образование молекулярного комплекса по типу: субстрат - нуклеофил. Найдены константы скорости и константы равновесия отдельных стадий. Обнаружено критическое значение концентрации пиперидина, при котором происходит смена лимитирующей скорость стадии. |
|
| Date |
2014-04-15T14:26:31Z
2014-04-15T14:26:31Z 2014 |
|
| Type |
Article
|
|
| Identifier |
УДК 541.121.124.127: 547.82
http://ea.donntu.edu.ua/handle/123456789/25976 |
|
| Language |
other
|
|
| Publisher |
Наукові праці ДонНТУ. Серія: Хімія і хімічна технологія. - 2014. - Вип. 1(22). - С. 98-105
|
|