Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Química / Made available in DSpace on 2012-10-26T12:27:55Z (GMT). No. of bitstreams: 1
302841.pdf: 3680662 bytes, checksum: 748bacb79b25a3c43bf0d51576fa796c (MD5) / As substituições nucleofílicas em ésteres de fosfato são amplamente estudadas na literatura. Os parâmetros estudados nestas reações são: sensibilidade ao grupo de saída e aos nucleófilos, medidas através de ?LG e ?Nu, respectivamente, a partir de Relações Lineares de Energia Livre (RLELs) de Brønsted. Quanto à reatividade de triésteres de fosfato, poucas evidências encontradas na literatura sugerem que grupos espectadores têm mínima influência. Neste trabalho foram preparados e estudadas as reações de hidrólise dos triésteres de fosfato tri-piridil fosfato (TPP), metil-di-piridil fosfato, di-etil-piridil fosfato, tri-4-nitrofenil fosfato (T4NPP), tri-3-nitrofenil fosfato (T3NPP) e tri-3-clorofenil fosfato (T3ClPP). A alta constante de hidrólise espontânea do TPP (2,2×10-5 s-1) e o alto efeito isotópico (kH/kD = 3,15) foram, inicialmente, interpretados como evidências de catálise básica geral intramolecular. Porém, estudos cinéticos posteriores com os triésteres triarílicos T4NPP, T3NPP e T3ClPP mostraram que os mesmos são mais reativos que sistemas di-alquil arílicos. Assim, os grupos espectadores, alquil ou aril, podem aparentemente contribuir em diferentes extensões para a reatividade dos triésteres de fosfato. A partir de RLELs de Brønsted, a influência dos grupos espectadores pode ser determinada e um novo parâmetro definido como ?NLG foi proposto para caracterizar a participação destes grupos. / In the present work phosphate triesters pyridyl tri-phosphate (9), di-ethyl-2-pyridyl phosphate (22), methyl-di-2-pyridyl (23) phosphate, tri-3 -nitrophenyl phosphate (25a) tri-4-nitrophenyl phosphate (25b), and tri-3-chlorophenyl phosphate (25c) were prepared. The spontaneous hydrolysis of the reactions containing the pyridyl group were studied under different conditions of temperature, pH and solvent. Due to low water solubility of the 25a-c, the hydrolyses reactions were followed in different mixtures of acetonitrile / water in order to obtain, by extrapolation, the constants of the spontaneous hydrolysis of each triester. The high value of spontaneous hydrolysis constant of triester 9 (2.2 × 10-5 s-1) and the high isotope effect (kH / kD = 3.15) were initially interpreted as evidence for intramolecular general base catalysis. However, subsequent kinetic studies with the triaryl phosphates 25a-c showed that these compounds are considerably more reactive than the corresponding dialkyl aryl system. Thus, the spectator groups, alkyl or aryl, can apparently contribute in different extents to the reactivity of phosphate triesters. So, in nucleophilic substitution reactions of phosphate triesters, besides the sensitivities to the leaving group and to the nucleophile, measured as ßLG and ßNu, respectively, the role of spectator groups becomes important. From Brønsted type linear free energy relationship # the influence of spectator groups can be determined, and a new parameter defined as ßNLG was proposed to characterize the participation of spectator groups. Regarding the reactivity of phosphate triesters, evidence found in the literature suggested that spectators groups had little or no influence and the correlation of Khan and Kirby had been used to calculate or predict the reactivity of these compounds. However, new evidence presented in this work indicate that triaryl phosphate triesters have reactivities that depend upon the spectator groups. The values of ßNLG found for triaryl and dialkyl aryl systems were 0.29 and 0.60 respectively. In fact, despite suffering smaller influence from spectator groups, the triaryl phosphate triesters are more reactive than di-alkyl aryl triesters and, the latter are more influenced by spectator groups. Finally, the results of this study add to existing literature new linear free energy correlations, clarifying and quantifying the effects of spectator groups in the hydrolysis of phosphate triesters, aspects previously considered unimportant in this type of reaction.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufsc.br:123456789/96477 |
| Date | January 2012 |
| Creators | Oliveira, Pedro Santos Mello de |
| Contributors | Universidade Federal de Santa Catarina, Nome Aguilera, Faruk José |
| Publisher | Florianópolis, SC |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | 148 p.| il., grafs., tabs. |
| Source | reponame:Repositório Institucional da UFSC, instname:Universidade Federal de Santa Catarina, instacron:UFSC |
| Rights | info:eu-repo/semantics/openAccess |
Page generated in 0.0026 seconds