TY - JOUR
T1 - Reaction mechanism of tert-butylation of phenol with tert-butyl alcohol over H-β zeolite
T2 - An ONIOM study
AU - Nie, Xiaowa
AU - Janik, Michael J.
AU - Guo, Xinwen
AU - Liu, Xin
AU - Song, Chunshan
N1 - Funding Information:
This work was financially supported by the program for New Century Excellent Talent in University ( NCET-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. Nie as a part of the collaborative research in the ongoing PSU-DUT Clean Energy Research Center efforts.
PY - 2011/5/16
Y1 - 2011/5/16
N2 - Tert-butylation of phenol with tert-butyl alcohol (TBA) over H-β zeolite was studied using the ONIOM approach with two proposed reaction paths: stepwise and concerted mechanisms. The results obtained by the ONIOM2 (B3LYP/6-31G(d,p):UFF) method reveals that the tert-butylation of phenol preferentially occurs through a co-adsorbed, concerted mechanism without prior dehydration of tert-butyl alcohol, rather than via a stepwise mechanism through dehydration to form tert-butyl carbenium ion as the first step followed by tert-butyl cation attack on the 2- or 4-position on phenol. The kinetic difference between 2- and 4-tert-butylation is more apparent in the concerted path, where 4-tert-butylation proceeds over a lower activation barrier. Decreasing the acid site strength, via substitution of Ga for Al, reduces the H-bonding interaction between the zeolitic proton and tert-butyl alcohol and increases the apparent activation barriers, which slows the overall reaction, and also lowers the selectivity to 4-tert-butyl phenol.
AB - Tert-butylation of phenol with tert-butyl alcohol (TBA) over H-β zeolite was studied using the ONIOM approach with two proposed reaction paths: stepwise and concerted mechanisms. The results obtained by the ONIOM2 (B3LYP/6-31G(d,p):UFF) method reveals that the tert-butylation of phenol preferentially occurs through a co-adsorbed, concerted mechanism without prior dehydration of tert-butyl alcohol, rather than via a stepwise mechanism through dehydration to form tert-butyl carbenium ion as the first step followed by tert-butyl cation attack on the 2- or 4-position on phenol. The kinetic difference between 2- and 4-tert-butylation is more apparent in the concerted path, where 4-tert-butylation proceeds over a lower activation barrier. Decreasing the acid site strength, via substitution of Ga for Al, reduces the H-bonding interaction between the zeolitic proton and tert-butyl alcohol and increases the apparent activation barriers, which slows the overall reaction, and also lowers the selectivity to 4-tert-butyl phenol.
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U2 - 10.1016/j.cattod.2010.11.070
DO - 10.1016/j.cattod.2010.11.070
M3 - Article
AN - SCOPUS:79955379103
SN - 0920-5861
VL - 165
SP - 120
EP - 128
JO - Catalysis Today
JF - Catalysis Today
IS - 1
ER -