557-75-5Relevant articles and documents
Simple Enols. 2. Kinetics and Mechanism of the Ketonization of Vinyl Alcohol
Capon, Brian,Zucco, Cesar
, p. 7567 - 7572 (1982)
The kinetics of the conversion of vinyl alcohol into acetaldehyde in aqueous solution at 15 deg C were found to depend on pH according to the equation k0 = kH2O + (kH+*10-pH) + (kOH-*kW)/10-pH where KH2O = 1.38*10-2 s-1, KH+ = 20.2 M-1 s-1, and KOH- = 1.50*107 M-1 s-1.Under the same conditions, KH+ for the hydrolysis of ethyl vinyl ether is 1.19 M-1 s-1.The solvent deuterium isotope effrect, KH+/kD+, for the ketonization of vinyl alcohol is 4.75 and for the hydrolysis of ethyl vinyl ether is 2.98; the entropies of activation for the two reactions are -13.3 (esd = 1.7) cal deg-1 mol-1 at 25 deg C.General-base catalysis (β = 0.77) was observed for the ketonization of vinyl alcohol with eight carboxylate ions, and general-acid catalysis (α = 0.45) was observed with five carboxylic acids stronger than and including formic acid.The variation of kH+ with solvent composition in H2O-Me2SO mixtures was much less for the ketonization of vinyl alcohol than for the hydrolysis of ethyl vinyl ether, and as result of this, kH+ for the former reaction is 325 times greater than for the latter in 92.5 mol percent Me2SO; the isotope effect kH+/kD+, for the two reactions in 85.9 mol percent Me2SO are 5.33 and 2.05.It is concluded that these experimental results are best explained by a mechanism for the acid-catalyzed ketonization of vinyl alcohol in which protonation of the double bond by the acid catalyst is concerted with removal of the enolic proton by water acting as a general base and by a mechanism for the base- and water-catalyzed reactions that involves a rate-limiting C-protonation of the enolate anion.The pKenol for acetaldehyde at 25 deg C was estimated to be 6.66 or 6.44 from the value of kH+ for the ketonization of vinyl alcohol determined in this investigation and previously reported values of kH+ for the enolization of acetaldehydeu
Solvent Effects in A1 and ASE2 Reactions in Water/2,2,2-Trifluoroethanol Mixtures
Parnell, Charles,Binder, David,Eliason, Robert
, p. 1118 - 1120 (1985)
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(Trans)esterification of mannose catalyzed by lipase B from candida antarctica in an improved reaction medium using co-solvents and molecular sieve
Nott, Katherine,Brognaux, Alison,Richard, Gaetan,Laurent, Pascal,Favrelle, Audrey,Jerome, Christine,Blecker, Christophe,Wathelet, Jean-Paul,Paquot, Michel,Deleu, Magali
, p. 348 - 363 (2012)
Four co-solvents (dimethylformamide [DMF], formamide, dimethyl sulfoxide [DMSO], and pyridine) were tested with tert-butanol (tBut) to optimize the initial rate (v0) and yield of mannosyl myristate synthesis by esterification catalyzed by immobilized lipase B from Candida antarctica. Ten percent by volume of DMSO resulted in the best improvement of v0 and 48-hr yield (respectively 115% and 13% relative gain compared to pure tBut). Use of molecular sieve (5% w/v) enhances the 48-hr yield (55% in tBut/DMSO [9:1, v/v]). Transesterification in tBut/DMSO (9:1, v/v) with vinyl myristate leads to further improvement of v0 and 48-hr yield: a relative gain of 85% and 65%, respectively, without sieve and 25% and 10%, respectively, with sieve, compared to esterification. No difference in v0 and 48-hr yield is observed when transesterification is carried out with or without sieve. Copyright Taylor & Francis Group, LLC.
Phosphorus and nitrogen-doped palladium nanomaterials support on coral-like carbon materials as the catalyst for semi-hydrogenation of phenylacetylene and mechanism study
Ma, Lei,Jiang, Pengbo,Wang, Kaizhi,Lan, Kai,Huang, Xiaokang,Yang, Ming,Gong, Li,Jia, Qi,Mu, Xiao,Xiong, Yucong,Li, Rong
, (2021/02/26)
In this work, two types of polyporous and coral-like materials (CN) with high specific surface area are prepared using sodium glutamate as a carrier. At the same time, a CN-supported phosphorus-nitrogen-doped palladium nanomaterial CN-P-Pd is synthesized and applied to the preparation of styrene by selective hydrogenation of phenylacetylene under mild conditions. As shown in the TEM images, Pd nanoparticles with a particle size of about 4.4 nm are uniformly dispersed on the surface of the carrier. The results of N2 adsorption–desorption reveal that the surface area of the prepared catalyst (CN-P-Pd) is 1307 m2g?1. In addition, the experimental exploration shows the intervention of P in carbon-nitrogen materials can contribute to improve the selectivity of the reaction, which can be attributed to the fact that P element can change the electron density of Pd. Meanwhile, it is found that the solvent not only affects the activity of catalyst, but also the selectivity of the reaction. Kinetic study shows the activation energy of the reaction is 4.5 kJ/mol. With the increase of the reaction temperature, the dissolution rate of hydrogen in the solvent gradually slows down, which inhibits the progress of the reduction reaction. Mechanistic studies demonstrate that the carbon-nitrogen materials have strong adsorption capacity for substrates, and also provide more adsorption sites for phenylacetylene. Additionally, the optimal catalyst (CN-P-Pd) also has high reaction activity to other alkynes and the conversion can reach at 95%. Moreover, the optimal catalyst can be reused several times without significant reduction in reaction activity.
Cutinase from Fusarium oxysporum catalyzes the acylation of tyrosol in an aqueous medium: Optimization and thermodynamic study of the reaction
Nikolaivits, Efstratios,Norra, Giannis-Florjan,Voutsas, Epaminondas,Topakas, Evangelos
, p. 29 - 36 (2016/04/20)
Recently, tyrosol has gained attention as a result of its many pharmacological properties and due to the fact that it can be isolated from cheap and abundant resources. Lipophilic tyrosyl esters, which are scarce in nature, have proven in certain cases to acquire improved biological activity compared to tyrosol itself, increasing their potential use in the food and cosmeceutical industries. The enzymatic approach for the synthesis of such esters has prevailed, as it is "green", compared to chemical practices. We hereby report the enzymatic synthesis of tyrosyl esters of various aliphatic fatty acids performed by a recombinant cutinase from Fusarium oxysporum (FoCut5a). The reaction system used consists of an aqueous phase saturated with the corresponding fatty-acid vinyl ester, which played the role of the acyl donor. We also proceeded to the study of several parameters on the yield of the tyrosyl butyrate ester synthesis. The maximum yield achieved was 60.7% after 4 h at 20 °C, in pH 7.0, with initial tyrosol concentration of 12.5 mM and using 5 μg FoCut5a mL-1 reaction as catalyst. The optimum reaction conditions can be considered mild, highlighting the environmentally friendly nature of this reaction, along with the fact that there are not any harmful reagents involved. Additionally, the use of two thermodynamic models, Conductor-like Screening Model for Real Solvents (COSMO-RS) and UNIquac Functional-group Activity Coefficients (UNIFAC), were employed for the prediction of reactants' and products' solubilities and their distribution in the reaction biphasic system, aiming to correlate the reaction yields with these important thermodynamic quantities and understand the ability of this enzymatic reaction in synthesizing tyrosyl esters.
