Banca de DEFESA: ISAC CAMILO NOGUEIRA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : ISAC CAMILO NOGUEIRA
DATE: 23/03/2023
TIME: 14:00
LOCAL: REMOTO
TITLE:

Theoretical Study of Mechanism and Kinetics of Alkylation Reactions of Aromatic Compounds Aiming to Design New Catalysts

KEY WORDS:

Williamson ether synthesis, O-alkylation, C-alkylation, Phenoxide ion, Solvent effect, Friedel-Crafts, Lewis acid

PAGES: 100
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Química Teórica
SUMMARY:

Experiments reported in the literature involving phenol alkylation under conditions of phase transfer catalysis support the formation of the R4N+PhO-(PhOH) complex in the organic phase. This complex may be directly involved in the transition state. In thepresent theoretical study, the phase transfer catalyzed alkylation of phenol was investigated using M06-2X/def2-TZVPP//X3LYP/def2/SVP level of calculation and including the solvent effect using the SMD model combined with reliable experimental data from free energy of solvation of ionic species in aqueous solution. The analysis was done for tetraethylammonium, tetrapropylammonium and tetrabutylammonium phase transfer catalysts. In the case of the tetrabutylammonium ion, the calculations predicted reaction kinetics compatible with the experimental data. Furthermore, the Bu4N+PhO-(PhOH) complex is calculated to be the active species in catalysis. For the tetraethylammonium and tetrapropylammonium cations, the R4N+PhO-and R4N+PhO-(PhOH) complexes are not able to explain the catalysis, suggesting that another more complex aggregate may be involved in the process. Aiming at the development of new catalysts for this reaction, we studied the modified crown ether catalysts (DBEC4OH), a variation of the Jadhav catalyst (BAC5CAt) and the Takemoto catalyst. In general, these catalysts were not very promising for this reaction, but the BAC5CAt catalyst that produces a free energy barrier equal to 21.50 kcal/mol in MIBK stands out, being a good candidate to promote selectivity for O-alkylation especially in nonpolar solvents. The classical alkylation reaction of benzene with isopropyl chloride catalyzed by AlCl3and Al2Cl6species was studied using the same level of theory used in phenol alkylation reactions. We evaluatedthe formation of dimers, trimers, tetramers and pentamers and showed that Al2Cl6dimers exist in greater proportion, according to experimental observations. The experimental solubility of Al2Cl6in benzene was also included in the theoretical kinetic analysis. The reaction catalyzed by the AlCl3 species presents the greatest barrier, in part due to the unfavorable dissociation of the Al2Cl6 species. The mechanism via catalysis with Al2Cl6is more efficient and, even considering its low solubility, the calculated observed ∆G‡is only 20.6 kcal/mol, indicating a high reaction rate. The mechanism involves the formation of the ionic pair CH3CHCH3+...Al2Cl7-, which reacts with benzene to form a Wheland intermediate, and this carbon-carbon bond formation step corresponds to the rate-determiningstep.

BANKING MEMBERS:
Externo à Instituição - LUCIANO TAVARES DA COSTA - UFF
Externo à Instituição - HEITOR AVELINO DE ABREU - UFMG
Presidente - 1623600 - JOSEFREDO RODRIGUEZ PLIEGO JUNIOR
Externa ao Programa - 1544781 - STELLA MARIS RESENDE
Interno - 1942302 - VICTOR AUGUSTO ARAUJO DE FREITAS