Mechanisms of Organocatalytic Amidation and Trans-Esterification of Aromatic Esters As a Model for the Depolymerization of Poly(ethylene) Terephthalate

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• 作者：Hans W. Horn ; Gavin O. Jones ; DiDi S. Wei ; Kazuki Fukushima ; Julien M. Lecuyer ; Daniel J. Coady ; James L. Hedrick ; Julia E. Rice
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：December 27, 2012
• 年：2012
• 卷：116
• 期：51
• 页码：12389-12398
• 全文大小：503K
• 年卷期：v.116,no.51(December 27, 2012)
• ISSN：1520-5215

文摘

We describe investigations with B3LYP density functional theory to probe mechanisms for the organocatalyzed depolymerization of poly(ethylene) terephthalate (PET) into ester and amide products. These investigations utilize model systems involving the trans-esterification and amidation of methylbenzoate (MB) with ethylene glycol (EG), ethylenediamine (EDA), and ethanolamine (EA) organocatalyzed by 1,5,7-triazabicyclododecene (TBD) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Mechanisms for reactions in which TBD acts as the lone catalyst have been compared with pathways in which TBD and DBU catalyze these processes with an additional molecule of the amine or alcohol acting as a cocatalyst. Calculations suggest that the combination of an organocatalyst with a molecule of an alcohol or amine cocatalyst is slightly more activating than a lone catalyst. Our results predict that nucleophilic attack is the rate-determining step in reactions involving EDA and EG and that TBD is a better catalyst than DBU in the amidation of MB with EDA; in addition, both organocatalysts activate alcohols more than amines during nucleophilic attack. Amidation and trans-esterification possess similar barriers for reactions involving EA; but the amide, which is the thermodynamic product, is preferentially formed instead of the ester.