4630-82-4Relevant articles and documents
Kinetic aspects of the effect of CO pressure and methanol concentration on cyclohexene hydrocarbomethoxylation in the presence of the Pd(PPh 3)2Cl2-PPh3-p-toluenesulfonic acid catalytic system
Aver'Yanov,Sevost'Yanova,Batashev,Demerlii
, p. 39 - 45 (2013)
The dependence of the rate of the cyclohexene hydrocarbomethoxylation reaction catalyzed by the Pd(PPh3)2Cl2-PPh 3-p-toluenesulfonic acid system on the CO pressure and methanol concentration at temperatures varied in the range of 358-388 K has been investigated. The data are interpreted in terms of the previously proposed mechanism involving as intermediates ion pairs containing cationic hydride, alkyl, and acyl palladium complexes. By the least squares technique, apparent constants relating to the effect of CO pressure and methanol concentration have been estimated for the rate equation derived earlier. The apparent activation energies have been determined for these constants, and the following stability series of palladium complexes has been proposed on their basis: Pd(PPh 3)2 (CO)2 > Pd(PPh3)4 > Pd(PPh3)2 (CH3OH)2 > H Sol⊕ [Pd(PPh3)2 (Cl)(Sol)].
The concentration effects of reactants and components in the Pd(OAc) 2/p-toluenesulphonic acid/trans-2,3-bis(diphenylphosphinomethyl)- norbornane catalytic system on the rate of cyclohexene hydrocarbomethoxylation
Nifant'Ev,Sevostyanova,Averyanov,Batashev,Vorobiev,Toloraya,Bagrov,Tavtorkin
, p. 145 - 152 (2012)
The reactants and components of a catalytic system were studied for their effects on the rate of Pd-catalysed cyclohexene hydrocarbomethoxylation. First-order reaction rate dependences were established for cyclohexene and Pd(OAc)2, while non-monotonic rate dependences were determined for the diphosphine and p-toluenesulphonic acid concentrations and the SO pressure. The reaction was shown to follow first-order kinetics when the methanol concentration was below 0.4 mol/L; however, the reaction rate slowed upon a further increase in the methanol concentration. The obtained results were interpreted by considering a hydride mechanism supplemented with ligand exchange reactions, which decreased the activity of the catalyst, and with hydride complex annihilations by p-toluenesulphonic acid, resulting in complete loss of catalytic activity. Treatment of the proposed mechanism using the quasi-equilibrium concentration method gave a kinetic equation for the reaction that was consistent with the experimental data.
Eidus et al.
, (1971)
Regioselective 6-endo cyclization of 5-carbomethoxy-5-hexenyl radicals: A convenient synthesis of derivatives of the 1-azabicyclo[2.2.1]heptyl system
Della, Ernest W.,Kostakis, Chris,Smith, Paul A.
, p. 363 - 365 (1999)
(equation presented) Ring closure of the 5-carbomethoxy-5-hexenyl radical is governed largely by the polar effect, and as predicted by frontier molecular orbital considerations, endo cyclization predominates, leading to cyclohexyl rather than cyclopentyl-based products. In cyclization of the corresponding β-ammonio species 18, stereoelectronic effects do not distinquish between attack of the radical center at C3 or C4, each of which represents a 5-exo ring closure. The radical 18 is found to cyclize with great rapidity and with high stereoselectivity to give bicyclo[2.2.1]heptane products in accordance with expectation based on polar effects; this transformation represents an excellent entry to the physiologically important bicyclic ester 17.
N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading
Berkessel, Albrecht,Biswas, Animesh,Harnying, Wacharee,Sudkaow, Panyapon
supporting information, p. 19631 - 19636 (2021/08/09)
We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered α- and β-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of α/β-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02–1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.
Oxidative esterification of alcohols by a single-side organically decorated Anderson-type chrome-based catalyst
Wang, Jingjing,Jiang, Feng,Tao, Chaofu,Yu, Han,Ruhlmann, Laurent,Wei, Yongge
supporting information, p. 2652 - 2657 (2021/04/21)
The direct esterification of alcohols with non-noble metal-based catalytic systems faces great challenges. Here, we report a new chrome-based catalyst stabilized by a single pentaerythritol decorated Anderson-type polyoxometalate, [N(C4H9)4]3[CrMo6O18(OH)3C{(OCH2)3CH2OH}], which can realize the efficient transformation from alcohols to esters by H2O2oxidation in good yields and high selectivity without extra organic ligands. A variety of alcohols with different functionalities including some natural products and pharmaceutical intermediates are tolerated in this system. The chrome-based catalyst can be recycled several times and still keep the original configuration and catalytic activity. We also propose a reasonable catalytic mechanism and prove the potential for industrial applications.
