- Phosphine-free cobalt catalyst precursors for the selective hydrogenation of olefins
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Cobalt(ii) complexes bearing phosphine-free tridentate NNS ligands were prepared. Depending on the ligand, dimeric or monomeric complexes were isolated. Monomeric Co(NNMeS)Cl2 selectively catalysed the hydrogenation of olefins in the presence of reducible moieties such as ketones. Further investigation showed that this complex functions as a nanoparticle precursor under the reaction conditions.
- Puylaert, Pim,Dell'Acqua, Andrea,El Ouahabi, Fatima,Spannenberg, Anke,Roisnel, Thierry,Lefort, Laurent,Hinze, Sandra,Tin, Sergey,De Vries, Johannes Gerardus
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- Three step auto-tandem catalysed hydroesterification: Access to linear fruity esters from piperylene
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A convenient and selective access to saturated hexanoic esters via hydroesterification of piperylene with synthesis gas and methanol is presented. This is the first three step auto-tandem hydroesterification, which is 100% atom economic proceeding under mild conditions. Our optimisations revealed Pd2(dba)3/1,2-dtbpmb as the best catalytic system. Besides, the reaction also tolerates several alcohols, which offers a broad range of fruity esters. In addition, we present insights into the reaction sequence, investigating whether the reaction proceeds via two- or three-step reaction cascade.
- Neubert, Peter,Steffen, Matthias,Behr, Arno
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p. 122 - 127
(2015/07/15)
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- Optimized synthesis of (Z)-3-hexen-1-yl caproate using germinated rapeseed lipase in organic solvent
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(Z)-3-hexen-1-yl esters are important green top-note components of food flavors and fragrances. Effects of various process conditions on (Z)-3-hexen-1-yl caproate synthesis employing germinated rapeseed lipase acetone powder in organic solvent were investigated. Rapeseed lipase catalyzed ester formation more efficiently with non-polar compared to polar solvents despite high enzyme stability in both types of solvents. Maximum ester yield (90%) was obtained when 0.125 M (Z)-3-hexen-1-ol and caproic acid were reacted at 25 °C for 48 h in the presence of 50 g/L enzyme in heptane. Enzyme showed little sensitivity towards aw with optimum yield at 0.45, while added water did not affect ester yield. Esterification reduced by increasing molecular sieves (>0.0125%, w/v). The highest yields of caproic acid were obtained with isoamyl alcohol (93%) followed by butanol and (Z)-3-hexen-1-o1 (88%) respectively reflecting the enzyme specificity for straight and branched chain alcohols. Secondary alcohols showed low reactivity, while tertiary alcohol had either very low reactivity or not esterified at all. A good relationship has been found between ester synthesis and the solvent polarity (log P value); while no correlation for the effect of solvents on residual enzyme activity was observed. It may be concluded that germinated rapeseed lipase is a promising biocatalyst for the synthesis of valuable green flavor note compound. The enzyme also showed a wide range of temperature stability (5-50 °C).
- Liaquat, Muhammad
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scheme or table
p. 59 - 65
(2011/07/31)
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- Ruthenium pincer-catalyzed acylation of alcohols using esters with liberation of hydrogen under neutral conditions
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Acylation of secondary alcohols using non-activated esters, in particular symmetrical esters (such as ethyl acetate), is achieved under neutral conditions with the liberation of molecular hydrogen. This unprecedented, environmentally benign reaction is homogenously catalyzed by a dearomatized ruthenium pincer PNN complex. Copyright
- Gnanaprakasam, Boopathy,Ben-David, Yehoshoa,Milstein, David
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supporting information; experimental part
p. 3169 - 3173
(2011/02/23)
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- Transfer hydrogenation of olefins catalysed by nickel nanoparticles
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Nickel nanoparticles have been found to effectively catalyse the hydrogen-transfer reduction of a variety of non-functionalised and functionalised olefins using 2-propanol as the hydrogen donor. The heterogeneous process has been shown to be highly chemoselective for certain substrates, with all the corresponding alkanes being obtained in high yields. A synthesis of the natural dihydrostilbene brittonin A?is also reported based on the use of nickel nanoparticles.
- Alonso, Francisco,Riente, Paola,Yus, Miguel
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experimental part
p. 10637 - 10643
(2010/01/16)
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- Facile and efficient oxidative transformation of primary alcohols to methyl esters in water using hypervalent iodine(III) reagents
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A facile and direct oxidative esterification of primary alcohols in water using a combination of the hypervalent iodine(III) reagent, iodosobenzene (PhIO), and KBr has been developed. This methodology is expected to be environmentally benign since it uses a recyclable polymer-supported iodine(III) reagent in water.
- Tohma, Hirofumi,Maegawa, Tomohiro,Kita, Yasuyuki
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p. 723 - 725
(2007/10/03)
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- Facile oxidation of aldehydes to acids and esters with Oxone
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(Matrix presented) A highly efficient, mild, and simple protocol is presented for the oxidation of aldehydes to carboxylic acids utilizing Oxone as the sole oxidant. Direct conversion of aldehydes in alcoholic solvents to their corresponding ester products is also reported. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations.
- Travis, Benjamin R.,Sivakumar, Meenakshi,Hollist, G. Olatunji,Borhan, Babak
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p. 1031 - 1034
(2007/10/03)
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- The Esterification of Carboxylic Acid with Alcohol over Hydrous Zirconium Oxide
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The esterification of carboxylic acids with alcohols proceeded efficienly with hydrous zirconium oxide to give the corresponding esters in the vapor phase, in the liquid phase, and in an autoclave.The steric hindrance of carboxylic acids and alcohols affected the esterification by lowering the reactivity.With a rise in the reaction temperature, the conversion of the carboxylic acid increased.The dehydration of alcohols was prevented by using hydrous zirconium oxide in spite of the high reaction temperature.The reaction rate is first-order with respect to the concentration of the catalyst and an alcohol and is inversely proportional to thta of the carboxylic acid.Transesterification also proceeded efficiently.
- Takahashi, Kyoko,Shibagaki, Makoto,Matsushita, Hajime
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p. 2353 - 2361
(2007/10/02)
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- Esterification of Carboxylic Acids Mediated by Chlorotrimethylsilane
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The reaction of aliphatic and aromatic carboxylic acids with alcohols in presence of chlorotrimethylsilane affords, under mild condition, the corresponding esters in excellent yields.The reaction can be extended to amino acids which also yield the amino esters in high yields.
- Mandal, Arun K.
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