100-67-4Relevant articles and documents
New Cu-based catalysts supported on TiO2 films for Ullmann SNAr-type C-O coupling reactions
Benaskar, Faysal,Engels, Volker,Rebrov, Evgeny V.,Patil, Narendra G.,Meuldijk, Jan,Thuene, Peter C.,Magusin, Pieter C. M. M.,Mezari, Brahim,Hessel, Volker,Hulshof, Lumbertus A.,Hensen, Emiel J. M.,Wheatley, Andrew E. H.,Schouten, Jaap C.
, p. 1800 - 1810 (2012)
New routes for the preparation of highly active TiO2-supported Cu and CuZn catalysts have been developed for C-O coupling reactions. Slurries of a titania precursor were dip-coated onto glass beads to obtain either structured mesoporous or non-porous titania thin films. The Cu and CuZn nanoparticles, synthesized using a reduction by solvent method, were deposited onto calcined films to obtain a Cu loading of 2 wt %. The catalysts were characterized by inductively coupled plasma (ICP) spectroscopy, temperature-programmed oxidation/reduction (TPO/TPR) techniques, 63Cu nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (S/TEM-EDX) and X-ray photo-electron spectroscopy (XPS). The activity and stability of the catalysts obtained have been studied in the C-O Ullmann coupling of 4-chloropyridine and potassium phenolate. The titania-supported nanoparticles retained catalyst activity for up to 12 h. However, catalyst deactivation was observed for longer operation times due to oxidation of the Cu nanoparticles. The oxidation rate could be significantly reduced over the CuZn/TiO2 catalytic films due to the presence of Zn. The 4-phenoxypyridine yield was 64 % on the Cu/nonporous TiO2 at 120 °C. The highest product yield of 84 % was obtained on the Cu/mesoporous TiO2 at 140 °C, corresponding to an initial reaction rate of 104 mmol gcat-1 s-1. The activation energy on the Cu/mesoporous TiO2 catalyst was found to be (144±5) kJ mol-1, which is close to the value obtained for the reaction over unsupported CuZn nanoparticles (123±3 kJ mol-1) and almost twice the value observed over the catalysts deposited onto the non-porous TiO2 support (75±2 kJ mol-1). Copyright
Enthalpy-entropy correlations in reactions of aryl benzoates with potassium aryloxides in dimethylformamide
Khalfina, Irina A.,Vlasov, Vladislav M.
, p. 266 - 282 (2013)
Temperature dependences of the relative reactivity of potassium aryloxides XC6H4O-K+ toward 4-nitrophenyl (1), 3-nitrophenyl (2), 4-chlorophenyl (3), and phenyl (4) benzoates in dimethylformamide (DMF) were studied using the competitive reactions technique. The rate constants kX for the reactions of 1 with potassium 4-cyanophenoxide, 2 with potassium 3-bromophenoxide, 3 with potassium 3-bromo-, 4-bromo-, and unsubstituted phenoxides, 4 with potassium 4-methoxy- and 3-methylphenoxides were measured at 25°C. Correlation analysis of the relative rate constants kX/kH(3-Me) and differences in the activation parameters (δδH≠and δ δS ≠) of competitive reactions revealed the existence of six isokinetic series. We investigated the substituent effect of X on the activation parameters for each isokinetic series and concluded that the reactions of aryl benzoates PhCO2C6H4Y with potassium aryloxides in DMF proceed via a four-step mechanism. The large ρ0(Y) and ρXY values at 25°C obtained for the reactions of 1-3 with potassium aryloxides with an electron-donating substituent refer to the rate-determining formation of the spiro-σ-complex. The Hammett plots for the reactions of 1 and 2 exhibit a downward curvature, causing the motion of the transition state for the rate-determining step according to a Hammond effect as the substituent in aryloxide changes from electron-donating to electron-withdrawing. Analysis of data in the terms of two-dimensional reaction coordinate diagrams leads to the conclusion that significant anti-Hammond effects arise in the cases of ortho-substituted and unsubstituted substrates. It was shown that the isokinetic and compensation effects observed for the reactions of aryl benzoates with potassium aryloxides in DMF can be interpreted in the terms of the electrostatic bonding between the reaction centers.
The unusual outcome of the reaction of potassium anions with phenyl glycidyl ether
Stolarzewicz, Andrzej,Grobelny, Zbigniew,Kowalczuk, Marek
, p. 111 - 114 (1995)
The formation of potassium phenolate, potassium hydroxide, propylene and ethylene in the reaction of phenyl glycidyl ether with the potassium anions has been demonstrated.Evidently, the PhO-CH2 bond is remarkably readily cleaved by the K- ion under these conditions.Keywords: Potassium anions; Crown ethers; Oxiranes
Impact of aryloxy initiators on the living and immortal polymerization of lactide
Chile,Ebrahimi,Wong,Aluthge,Hatzikiriakos,Mehrkhodavandi
, p. 6723 - 6733 (2017/07/10)
This report describes two different methodologies for the synthesis of aryl end-functionalized poly(lactide)s (PLAs) catalyzed by indium complexes. In the first method, a series of para-functionalized phenoxy-bridged dinuclear indium complexes [(NNO)InCl]2(μ-Cl)(μ-OPhR) (R = OMe (1), Me (2), H (3), Br (4), NO2 (5)) were synthesized and fully characterized. The solution and solid state structures of these complexes reflect the electronic differences between these initiators. The polymerization rates correlate with the electron donating ability of the phenoxy initiators: the para-nitro substituted complex 5 is essentially inactive. However, the para-methoxy variant, while less active than the ethoxy-bridged complex [(NNO)InCl]2(μ-Cl)(μ-OEt) (A), shows sufficient activity. Alternatively, aryl-capped PLAs were synthesized via immortal polymerization of PLA with A in the presence of a range of arylated chain transfer agents. Certain aromatic diols shut down polymerization by chelating one indium centre to form a stable metal complex. Immortal ROP was successful when using phenol, and 1,5-naphthalenediol. These polymers were analysed and chain end fidelity was confirmed using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and UV-Vis spectroscopy. This study shed light on possible speciation when attempting to generate PLA-lignin copolymers.
Gold phenolate complexes: Synthesis, structure, and reactivity
Ibrahim, Nada,Vilhelmsen, Mie Hojer,Pernpointner, Markus,Rominger, Frank,Hashmi, A. Stephen K.
, p. 2576 - 2583 (2013/06/26)
Seven different NHC gold(I) phenolate complexes were synthesized. Structural data, including X-ray crystal structure analyses, could be obtained for each of them. An investigation by computational chemistry, including NBO analysis, indicates three-center-four-electron hyperbonds among the carbene carbon, the gold atom, and the oxygen atom of the phenolate with an approximate 60:40 distribution of the bonding interaction in favor of the carbene-gold bond. The new class of complexes shows only moderate catalytic activity.
