- Dba-free palladium intermediates of the Heck-Matsuda reaction
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The dba-free Heck-Matsuda reaction was investigated via direct ESI-MS(/MS) monitoring. Palladium species involved in the reduction of Pd(ii) during a Wacker type reaction and several dba-free arylpalladium transient complexes were detected and characterized. Based on these findings, a more comprehensible catalytic cycle for this pivotal reaction is suggested.
- MacHado, Angelo H. L.,Milagre, Humberto M. S.,Eberlin, Livia S.,Sabino, Adao A.,Correia, Carlos Roque D.,Eberlin, Marcos N.
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Read Online
- Apixaban intermediate preparing method
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The present invention belongs to the field of pharmaceutical synthesis and relates to an apixaban intermediate preparing method. The intermediate is further used for preparing apixaban. The method issimple to operate, a product is high in yield and high i
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Paragraph 0010; 0024; 0025
(2020/05/01)
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- Inhibition of Acid-induced decomposition of diphenyltriazenes by complexation with cyclodextrins
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Acid-promotedN Nbond cleavage in 1,3-diphenyltriazenes (X-Ph-N=N-NH-Ph-X X = H, 4-OCH3), leading to formation of diazonium ions and anilines, is strongly inhibited in aqueous solutions in the presence of cyclodextrins (CDs). The inhibition is ascribed to the formation of inclusion complexes that render the guest diphenyltriazene significantly less basic as a result of the less polar nature of the CD cavity (amicrosolvent effect). Association equilibrium constants for 1:1 host-guest complexes increase in the order α-CD 3 being larger than those for X = H. In the case of α-CD, formation of 2:1 host-guest complexes is also involved.
- Xu, Tingting,Asadi, Atefeh Vaez-Zadeh,Barra, Monica
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supporting information; experimental part
p. 567 - 574
(2011/04/26)
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- Substituent effects on the thermal cis-to-trans isomerization of 1,3-diphenyltriazenes in aqueous solution
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The thermal cis-to-trans isomerization of some symmetrically p,p′-disubstituted 1,3-diphenyltriazenes has been studied by means of laser-flash photolysis techniques. The geometric isomerization is catalyzed by general acids and general bases as a result of acid/base-promoted 1,3-prototropic rearrangements. Acid catalysis becomes more prominent as the electron-donating character of the para substituent increases, while base catalysis becomes more important as the electron-withdrawing character of the para substituent increases. In addition, the rate ascribed to the interconversion of neutral cis rotamers through hindered rotation around the nitrogen-nitrogen single bond is found to decrease as the electron-withdrawing character of the para substituent increases. Rates of interconversion of neutral cis rotamers are also found to decrease with decreasing solvent polarity, which is indicative of the involvement of a polar transition state. On the other hand, kinetic investigations of the acid-catalyzed decomposition of target triazenes are consistent with an A1 mechanism.
- Chen, Nan,Barra, Monica,Lee, Ivan,Chahal, Navjot
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p. 2271 - 2277
(2007/10/03)
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- Pulsed Ultraviolet Laser Photolysis of Substituted Phenyl Diazosulphonates at 248 nm
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The photochemical decomposition of aqueous phenyl diazosulphonate solutions by KrF excimer laser pulses at 248 nm is investigated.The present study complements earlier investigations (Franzke et al. 1991, 1992) of the photochemistry of this class of compounds induced by irradiation at 308 nm (XeCl excimer laser), and in the 370-390 nm wavelength range (dye laser pulses).From the comparison, conclusions with regard to the wavelength dependent photolysis pathway are drawn.Phenyl diazosulphonates carrying methoxy- or ester-type substituents at the aromatic ring are observed to decompose in a two-step-reaction in aqueous solution: Photolysis proceeds via the phenyl diazonium ion as an intermediate, to yield the corresponding phenol as product.In contrast, the photolysis of 3-vinyl-phenyl diazosulphonate in aqueous solution at 248 nm results in a complex reaction involving via more than one intermediate.UV spectra recorded during photolysis show that products characterized by an absorption maximum at 272 nm are formed; these spectra are identical with those of final products from 308 nm photolysis, which are identified as 3-hydroxyethyl-phenols. - The photolysis pathway of 4-hydroxy-phenyl-diazosulphonate is found to proceed via the diazoquinone, instead of a diazonium ion.As a consequence of the high energy of 248 nm photons, the mentioned substituted phenols are not the final products of the photochemical reaction.These molecules are further decomposed by absorbing 248 nm photons; the quantum efficiency of these secondary photochemical reactions is lower by one to two orders of magnitude, as compared to the primary photolysis of the parent compounds. - Keywords: Light, Absorption / Materials Properties, Diazo Sulphonates / Photochemistry / Radicals / Spectroscopy, Ultraviolet
- Nomayo, M.,Wokaun, A.
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p. 1495 - 1503
(2007/10/02)
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- Dediazoniations of Arenediazonium Ions. Part 25. Influence of Substituents on the Exchange of the Diazonio Group for External Molecular Nitrogen and on the N(α),N(β)-Rearrangement in the Diazonio Group.
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The N(α), N(β)-rearrangement of the two N-atoms which can be observed in solutions of -labelled p-substituted benzenediazonium ions follows dual substituent parameter treatments.The reaction yields a negative field and positive resonance reaction constant (ρF = -3.35, ρR = 2.47).The magnitude of these constants is, within experimental error, the same as the respective reaction constants for solvolytic dediazonation.The exchange of the diazonio group of 15N-labelled p-substituted benzenediazonium ion yields, however, field and resonance reaction constants for the forward and reverse steps in the complex mechanism of the exchange reaction.
- Ravenscroft, Michael D.,Zollinger, Heinrich
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p. 507 - 514
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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