Decomposition of used poly(ethylene terephthalate) (PET) bottles was accomplished by methanolytic degradation using bamboo leaf ash (BLA) as a green and highly efficient heterogeneous catalytic system. The reaction at 200 °C in an autoclave reactor gave dimethyl terephthalate (DMT) and ethylene glycol (EG) in 78% and 76% yields, respectively. The chemical and physical characteristics of the prepared catalyst were studied using X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractograms (XRD), Energy dispersive X-ray spectrometry (EDX), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermal Gravimetric Analysis (TGA) and Brunauer-Emmett-Teller (BET) analyses. The conversion of PET to DMT and EG was completed within 2 h, and the crude as well as the recrystallized products were characterized using HPLC, NMR and IR. The catalyst, owing to its excellent thermal stability, mesoporous nature, bio-compatibility, cost free, easy preparation, recyclability and efficacy make it an attractive alternative and greener solid catalyst for PET depolymerization.
The semi-empirical PM3 SCF-MO method is used to investigate the Wagner-Meerwein migration of various groups during the pinacol-pinacolone rearrangement of some acyclic systems. Pinacol first protonates and dehydrates to form a carbocation that undergoes a 1,2-migration to form a protonated ketone, which then deprotonates to yield the pinacolone product. We study the Wagner-Meerwein migration of hydride, methyl, ethyl, isopropyl, t-butyl, phenyl and heterocylic 2-, 3-and 4-pyridyl groups in various acyclic 1,2-diol (pinacol) systems as they rearrange to pinacolones. This 1,2-migration involves a three-centred moiety in the cationic transition state. The migratory aptitude predicted here follows the order: hydride > t-butyl > isopropyl > ethyl > methyl > phenyl, which accords well with available experimental data and/or chemical intuition, reflecting also on the ability of the group involved to carry positive charge in the transition state. The structure of the migrating group (whether aliphatic or aromatic) within the transition state also supports the stabilising role of delocalisation of positive charge for reaction feasibility. Geometrical and thermodynamic considerations coincide in assigning the following order to relative "earliness" of the transition state along the reaction pathway: t-butyl > isopropyl > phenyl > methyl > 2-pyridyl > 4-pyridyl.
In this work, we discuss the valorization of biomass waste-derived orange peel ash (OPA) by exploring its applicability as a heterogeneous catalyst in aqueous aldol reaction and demonstrating its versatility...
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