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CIR-FTIR Studies of Palladium-Catalyzed Carboalkoxylation Reactions
Published in Dale W. Blackburn, Catalysis of Organic Reactions, 2020
William R. Moser, Andrew W. Wang, Nicholas K. Kildahl
Current mechanistic studies of this reaction in our laboratory have been centered around closely examining the mechanistic steps suggested in the literature to determine their feasibility on a stoichiometric basis and their consistency with the data measured under catalytic conditions. For the purposes of this study, the carbomethoxylation of bromobenzene with methanol and triethylamine to produce methyl benzoate was chosen as a model system. In situ infrared spectra obtained via cylindrical internal reflectance-Fourier transform infrared spectroscopy (CIR-FTIR) have proven invaluable in monitoring the dominant catalytic intermediates and measuring the rates of catalytic processes.36-40 In this technique, the incident infrared beam is directed onto the conical end of a cylindrical silicon rod. The reactor used in these studies is constructed in such a way that this silicon element passes directly through the reacting solution and out the other side (see Fig. 3). As the infrared beam travels through the infrared element, it undergoes a series of “reflections” off the interface between the silicon and its surroundings. At each reflection, the infrared radiation penetrates into the surrounding medium in accordance with the principles of attenuated total reflectance41; thus infrared absorbances of the surrounding medium are detected by the infrared beam. The transmitted beam from the end of the element is directed by mirrors to the infrared detector.
Organocatalysis with carbon nitrides
Published in Science and Technology of Advanced Materials, 2023
Sujanya Maria Ruban, Kavitha Ramadass, Gurwinder Singh, Siddulu Naidu Talapaneni, Gunda Kamalakar, Chandrakanth Rajanna Gadipelly, Lakshmi Kantham Mannepalli, Yoshihiro Sugi, Ajayan Vinu
Verma and his colleagues demonstrated direct esterification of alcohols by C-H activation utilizing several transition metal-impregnated g-C3N4 materials [171]. It was observed that even after a 24-h reaction, the reaction with Fe3O4@g-C3N4 produced no ester but just benzaldehyde. The copper (Cu@g-C3N4) and silver (Ag@g-C3N4) impregnated g-C3N4 materials do not affect the reaction. Pd@gC3N4 gave a 35% yield of methyl benzoate since the reaction did not complete; the remaining benzyl alcohol was transformed into aldehyde and the corresponding acid. Further, vanadium-based g-C3N4 catalysts gave better results under photochemical circumstances owing to their semiconductor behavior (Table 13) [172]. The VO@g-C3N4 was prepared by calcining urea at 500°C for 3 h and then dispersing it in a methanolic solution of vanadyl acetylacetonate [VO(acac)2] under sonication. It was demonstrated that 98% methyl benzoate yield was obtained by oxidative esterification via photocatalytic C-H activation of benzyl alcohol with methanol utilizing H2O2 as an oxidant and VO@g-C3N4 in methanolic medium and under visible illumination. Only a trace quantity of oxidative esterification product was produced during the control reaction using pure V2O5, demonstrating that g-C3N4 is not only hydrogenizing the V2O5 but also functioning as a promoter under photochemical conditions. The g-C3N4 operates as a basic surface to speed up C-H activation and esterification. The built-in photoactive chromophore would absorb energy and help to cross the activation energy barrier, allowing esterification to occur [173].
Kinetic modeling of benzoic acid esterification using functionalized silica gel
Published in Chemical Engineering Communications, 2018
In the presence of an acid catalyst, benzoic acid reacts with methanol to form methyl benzoate and water. The first-order kinetic model was used: where γA is the concentration of benzoic acid, t time, and k reaction rate constant. By integration of Eq. (1) we get: