Ortho-selective vapour phase methylation of phenol with methanol has been carried out over Zn (1−x) Mn x Fe 2 O 4 (x = 0, 0.25, 0.5, 0.75, 1.0) in the temperature range 423-698K in a fixed-bed, downflow reactor. o-Cresol and 2,6-xylenol were found to be the major products. Reaction parameters were optimized over MnFe 2 O 4 (MF). Maximum yields of 68.3% and 14% with selectivities of 81% and 17% were obtained for 2,6-xylenol and o-cresol respectively, giving a total selectivity of 98% over MnFe 2 O 4 at 598K, methanol to phenol molar ratio 6, and 0.4 h −1 weight hour space velocity. It was found that the product selectivity is greatly influenced by the acido-basic properties of the catalysts. o-Cresol formation is favoured over catalysts with weak acid sites whereas formation of 2,6-xylenol occurs in the presence of stronger acid sites. Catalyst characterization has been carried out by X-ray diffraction, infrared spectroscopy and ammonia desorption methods. X-ray diffractograms were used to determine the unit cell length and correlated with the acidity and catalytic activity of the spinel systems. IR absorption bands observed around 700 cm −1 and 500 cm −1 are respectively attributed to the tetrahedral and octahedral metal-oxygen stretching mode of the spinel. Shifting of bands towards lower wave numbers is correlated with composition and acidity of the spinel systems. The results are discussed on the basis of the Zn 2+ and Mn 2+ composition and acidity of the spinel systems.
Influence of the metal center on hydrolysis of organometallic
anticancer
complexes containing an N-phenyl-2-pyridinecarbothioamide
(PCA) ligand, [M(η6-p-cymene)(N-phenyl-2-pyridinecarbothioamide)Cl]
+
(M = RuII, 1A, and OsII, 2A), as well as their N-fluorophenyl
derivatives [M(η6-p-cymene)(N-fluorophenyl-2-pyridinecarbothioamide)Cl]
+
(M = RuII, 1B, and OsII, 2B) have been investigated using the DFT method in
aqueous medium. The activation energy barriers for the hydrolysis
of 1A (21.5 kcal/mol) and 1B (20.7 kcal/mol)
are found to be significantly lower than those of their corresponding
osmium analogs 2A (28.6 kcal/mol) and 2B (27.5 kcal/mol). DFT evaluated results reveal the inertness of Os(II)–PCA
complex toward the hydrolysis that rationalizes the experimental observations.
However, the incorporation of fluoride substituent slightly decreases
the activation energy for the hydrolysis of Ru(II)– and Os(II)–PCA.
In addition, the interaction of hydrolyzed Ru(II)–PCAs (1AH and 1BH) and Os(II)–PCAs (2AH and 2BH) complexes with the histidine (Hist) have also been investigated. The aquated 1BH and 2BH show an enhanced propensity toward the interaction with
histidine, and their activation Gibbs free energies are calculated
to be 15.9 and 18.9 kcal/mol, respectively. ONIOM (QM/MM) study of
the resulting aquated complexes inside histone protein shows the maximum
stability of the 2BH complex having a binding energy
of −43.6 kcal/mol.
Umpolung-based organocatalysis has
made a remarkable breakthrough
in the field of synthetic organic chemistry. Among a plethora of umpolung
catalysts, bis(amino)cyclopropenylidenes (BACs) have emerged as efficient
organocatalysts with potential applications in synthesizing numerous
essential organic moieties. In this study, a plausible mechanism for
bis(diethylamino)cyclopropenylidene (Et-BAC)-catalyzed synthesis of
α,α′-diarylated ketones has been
established using the density functional theory (DFT) method. The
proposed catalytic cycle of the studied reaction initiates with the
nucleophilic interaction of Et-BAC with p-chlorobenzaldehyde
to form a zwitterionic intermediate, which is then transformed to
a reactive Breslow intermediate. The Breslow intermediate further
undergoes a chemoselective and stereoselective 1,6-conjugate addition
reaction with p-quinone methide to form a new C–C
bond connection. Finally, the generated adduct undergoes a proton
shift reaction with the assistance of both 8-diazabicyclo(5.4.0)undec-7-ene
(DBU) and protonated DBU to yield the desired product. Conceptual
DFT-derived reactivity indices and frontier molecular orbital theory
analysis have been successfully utilized to unravel the role of Et-BAC
in this studied reaction. In addition to Et-BAC, DBU and protonated
DBU also play a very important role in lowering the activation energy
barrier of proton transfer steps. This investigation will help in
the rational designing of simple nonheterocyclic carbene-mediated
novel organic transformations.
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