TY - JOUR
T1 - Brønsted acid-catalyzed tert-butylation of phenol, o-cresol and catechol
T2 - A comparative computational study
AU - Nie, Xiaowa
AU - Liu, Xin
AU - Song, Chunshan
AU - Guo, Xinwen
N1 - Funding Information:
This work was financially supported by the program for New Century Excellent Talent in University (NECT-04-0268) and the Plan 111 Project of the Ministry of Education of China. The authors also thank the Pennsylvania State University for partial financial support for X.W.N. as a part of the collaborative research in the ongoing PSU-DUT Clean Energy Research Center efforts.
PY - 2010/11/1
Y1 - 2010/11/1
N2 - SO3H-functionalized ionic liquids (FILs) have been used to catalyze the alkylation of phenol, o-cresol and catechol with tert-butyl alcohol (TBA), and the catalytic performances are promising. During these Brønsted acid-catalyzed tert-butylations, t-butyl phenol ether (TBPE) and t-butyl o-cresol ether (TBOCE) are found, but no t-butyl catechol ether (TBCE) is detected. With the help of density functional theory (DFT) calculations, the reaction mechanisms of Brønsted acid-catalyzed tert-butylation of phenol, o-cresol and catechol were examined. The steric effect of t-butyl group does not have an apparent impact on the regioselectivity to t-butyl ether. The differences in the stability of O-alkylation intermediates, resulted from different ortho-substituents, account for the regioselectivity to t-butyl ether. For catechol tert-butylation, an intramolecular hydrogen bond is formed within the O-alkylation intermediate, which leads to extra stability of this intermediate and obvious increase of the activation barrier for TBCE formation. The intramolecular hydrogen bond formed within the O-alkylation intermediate facilitates its isomerization, inhibits the TBCE formation, thus making the reaction kinetics for catechol tert-butylation unique.
AB - SO3H-functionalized ionic liquids (FILs) have been used to catalyze the alkylation of phenol, o-cresol and catechol with tert-butyl alcohol (TBA), and the catalytic performances are promising. During these Brønsted acid-catalyzed tert-butylations, t-butyl phenol ether (TBPE) and t-butyl o-cresol ether (TBOCE) are found, but no t-butyl catechol ether (TBCE) is detected. With the help of density functional theory (DFT) calculations, the reaction mechanisms of Brønsted acid-catalyzed tert-butylation of phenol, o-cresol and catechol were examined. The steric effect of t-butyl group does not have an apparent impact on the regioselectivity to t-butyl ether. The differences in the stability of O-alkylation intermediates, resulted from different ortho-substituents, account for the regioselectivity to t-butyl ether. For catechol tert-butylation, an intramolecular hydrogen bond is formed within the O-alkylation intermediate, which leads to extra stability of this intermediate and obvious increase of the activation barrier for TBCE formation. The intramolecular hydrogen bond formed within the O-alkylation intermediate facilitates its isomerization, inhibits the TBCE formation, thus making the reaction kinetics for catechol tert-butylation unique.
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U2 - 10.1016/j.molcata.2010.09.010
DO - 10.1016/j.molcata.2010.09.010
M3 - Article
AN - SCOPUS:78049314621
SN - 1381-1169
VL - 332
SP - 145
EP - 151
JO - Journal of Molecular Catalysis A: Chemical
JF - Journal of Molecular Catalysis A: Chemical
IS - 1-2
ER -