- On the mechanism of the hydrocarbalkoxylation of olefins catalyzed by palladium complexes
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The acyl complex PdCl(COR)(PPh3)2 (R = Et, n-Hex), isolated during the course of hydrocarbalkoxylation reactions catalyzed by the precursor system PdCl2(PPh3)2-PPh3 (95 deg C, P(CO) 100-120 atm; Pd:P = 1 : 3-4), in ethanol or higher alkanols as solvents, reacts with an alkanol R'OH in the presence of added PPh3 (Pd:P = 1 : 3) to yield the ester RCOOR' and a mixture of PdCl2(PPh2)2 and Pd(PPh3)3 or 4.Moreover, when it is employed as catalyst precursor (R = n-Hex; Pd:P = 1:4) in the hydrocarbalkoxylation of ethylene, it is recovered as its ethyl analog and it yields almost stoichiometric amounts of n-HexCOOR'.When the dicarbomethoxy complex PdCl(COOMe)(PPh3)2, isolated in mixture with PdCl(COR)(PPh3)2 in hydrocarbomethoxylation experiments, is treated with 1-hexene in methanol (Pd:P:1-hexene:MeOH = 1:3:40:125), under nitrogen, in the absence of carbon monoxide, at 95 deg C, methyl heptanoate ester is not formed, and the starting complex is recovered almost quantitatively (92percent).When PdCl2(PPh3)2 or PdCl(COOMe)(PPh3)2 are used as catalyst precursors for the carbonylation of 1-hexene in MeOH, in the absence of added PPh3 and in the presence of NEt3 or of carboxylic acid anions (both of them are known to favor the formation of the carbomethoxy complex), no catalytic activity is observed and the precursors are recovered as palladium(0)carbonylphosphine complexes, ultimately mixed with the carbomethoxy complex. The results support the view that, of the two commonly accepted mechanisms for the catalytic hydrocarbalkoxylation of olefins, involving M-H or M-COOR' addition to the olefinic double bond, only the first one, in which a key intermediate is a Pd-acyl species, is probably involved. When n-BuOH is used as solvent the catalytic activity remains high even after 5-6 reuses of the catalyst, whereas in MeOH the activity falls significantly below its initial value because of decomposition of the catalyst into inactive palladium(0) complexes and palladium metal, probably via a carbomethoxypalladium complex.
- Cavinato, G.,Toniolo, L.
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- Cross-Dehydrogenating Coupling of Aldehydes with Amines/R-OTBS Ethers by Visible-Light Photoredox Catalysis: Synthesis of Amides, Esters, and Ureas
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A straightforward synthesis of amides, ureas, and esters is reported by visible-light cross-dehydrogenating coupling (CDC) of aldehydes (or amine carbaldehydes) and amines/R-OTBS ethers by photoredox catalysis. The reaction is found to be general and high yielding. A plausible mechanistic pathway has been proposed for these transformations and is supported by appropriate controlled experiments.
- Pandey, Ganesh,Koley, Suvajit,Talukdar, Ranadeep,Sahani, Pramod Kumar
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supporting information
p. 5861 - 5865
(2018/09/21)
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- Synthesis of carboxylic acid esters in the presence of micro- and mesoporous aluminosilicates
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The catalytic properties of zeolites HY, HBeta, and HZSM-12 and of mesoporous amorphous aluminosilicate in liquid-phase esterification of aliphatic (monobasic C1-C18, dibasic C6, C10) and aromatic (benzoic, trimellitic, phthalic) carboxylic acids with butanol were studied. Zeolite HBeta appeared to be the most active catalyst. Procedures were developed for preparing esters in the presence of zeolitic catalyst HBeta, ensuring 100% selectivity of ester formation at 90-98% conversion of the acid.
- Grigor'Eva,Suleimanova,Agliullin,Kutepov
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p. 773 - 779
(2015/01/30)
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- Oligomerization of acrylic acid derivatives by a reaction with the alkylcopper(I)phosphine complex
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Reaction of alkylcopper(I)phosphine complexes with electron-deficient olefins effected preferentially the products based on oligomerization, e.g. the product obtained by sequential conjugated addition, trimerization and cyclization from methyl methacrylate and the dimerization product from butyl acrylate.
- Mitani, Michiharu,Pakjamsai, Chitsakon,Tsuchida, Teruko,Kudoh, Hidekazu
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p. 112 - 128
(2007/10/03)
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- Catalytic processes of oxidation by hydrogen peroxide in the presence of Br2 or HBr. Mechanism and synthetic applications
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The mechanism and the synthetic applications for the oxidation of alcohols, ethers, and aldehydes by H2O2 catalyzed by Bf2 or Br- in a liquid two-phase system (aqueous and organic) are reported. Aliphatic and benzylic primary alcohols and ethers show an opposite behavior, which has been rationalized on the ground of the different electronic configurations of the intermediate alkyl (π-type) and acyl (σ-type) radicals and their influence on enthalpic and polar effects. A two-phase system is particularly useful also for an efficient benzylic bromination by Br2 or Br-; the substitution of the benzyl bromide by OH, OR, and OCOR regenerates Br-, which can be recycled. The evaluation of the relative reactivities of the involved substrates and intermediates has allowed to develop a variety of simple, facile, convenient, and selective syntheses of alcohols, aldehydes, ketones, esters, and benzyl bromides, which fulfill the conditions for practical applications.
- Amati, Alessandro,Dosualdo, Gabriele,Zhao, Lihua,Bravo, Anna,Fontana, Francesca,Minisci, Francesco,Bjorsvik, Hans-Rene
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p. 261 - 269
(2013/09/08)
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- β-Hydroxyethyl ester as a protecting group for carboxylic acids
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Use of β-hydroxyethyl esters as protecting groups for carboxylic acids is demonstrated.Their easy transesterification is also shown.
- Puntambekar, Hemalata M.,Naik, D. G.,Kapadi, A. H.
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p. 684 - 687
(2007/10/02)
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- Mono- and Bi-metallic Catalysed Formate-Halide Carbonylation Reactions
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Benzylic, aryl, and alkyl halides react with formate esters and carbon monoxide, in the presence of the dimer of chloro(hexa-1,5-diene)rhodium(I), 2, to give carboxylic esters: bimetallic catalysis 2> is particularly beneficial when an aromatic halide is used as the substrate.
- Buchan, Caroline,Hamel, Nathalie,Woell, James B.,Alper, Howard
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p. 167 - 168
(2007/10/02)
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- Quarternary Ammonium Salts for Butylation and Mass Spectral Identification of Volatile Organic Acids
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The esterification method described by Greeley (J.Chromatogr. 1974, 88, 229) was modified to overcome the problem of volatile acid evaporation during sample workup procedures.After solvent extraction from an aqueous sample, the acids were converted to their butyl ester derivatives in a two step process.Firstly, an involatile quarternary ammonium salts was formed which allowed concentration by solvent evaporation without loss of volatile acids.The acid salts were then converted to butyl esters by heating in the presence of n-butyl bromide and the esters were separated on a support- coated open tabular (SCOT) OV17 capillary column.The recovery and butylation yield were shown to be quantitative for isobutyric acid and the linearities and limits of detection are given for the five C4-C5 aliphatic acids.The mass spectra of butyl esters contain abundant rearrangement ions not present in methyl, ethyl, trimethylsilyl, or aryl esters which enable their rapid identification.The method was applied to the analysis of volatile urinary acids from a patient with Maple Syrup Urine Disease and showed conclusively the presence of both 2-methylbutyric and isovaleric acids.
- Burke, Daniel G.,Halpern, Berthold
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p. 822 - 826
(2007/10/02)
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