Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/198492
Type: Artigo de periódico
Title: Brønsted Acid Catalyzed Morita-baylis-hillman Reaction: A New Mechanistic View For Thioureas Revealed By Esi-ms(/ms) Monitoring And Dft Calculations.
Author: Amarante, Giovanni W
Benassi, Mario
Milagre, Humberto M S
Braga, Ataualpa A C
Maseras, Feliu
Eberlin, Marcos N
Coelho, Fernando
Abstract: A Morita-Baylis-Hillman (MBH) reaction catalyzed by thiourea was monitored by ESI-MS(/MS) and key intermediates were intercepted and characterized. These intermediates suggest that thiourea acts as an organocatalyst in all steps of the MBH reaction cycle, including the rate-limiting proton-transfer step. DFT calculations, performed for a model MBH reaction between formaldehyde and acrolein with trimethylamine as base and in the presence or the absence of thiourea, suggest that thiourea accelerates MBH reactions by decreasing the transition-state (TS) energies through bidentate hydrogen bonding throughout the whole catalytic cycle. In the rate-limiting proton-transfer step, the thiourea acts not as a proton shuttle, but as a Brønsted acid stabilizing the basic oxygen center that is formed in the TS.
Subject: Acids
Catalysis
Computer Simulation
Hydrogen Bonding
Kinetics
Molecular Structure
Protons
Spectrometry, Mass, Electrospray Ionization
Stereoisomerism
Tandem Mass Spectrometry
Thiourea
Rights: fechado
Identifier DOI: 10.1002/chem.200900966
Address: http://www.ncbi.nlm.nih.gov/pubmed/19813234
Date Issue: 2009
Appears in Collections:Unicamp - Artigos e Outros Documentos

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