29456-04-0Relevant articles and documents
Vinyl Alcohol: Generation and Decay Kinetics in Aqueous Solution and Determination of the Tautomerization Equilibrium Constant and Acid Dissociation Constants of the Aldehyde and Enol Forms
Chiang, Y.,Hojatti, M.,Keeffe, J. R.,Kresge, A. J.,Schepp, N. P.,Wirz, J.
, p. 4000 - 4009 (1987)
Vinyl alcohol was generated in aqueous solution by Norrish type II photoelimination of 5-hydroxy-2-pentanone and by the acid-catalyzed hydrolysis of a ketene acetal (1-(vinyloxy)-1-methoxyethene) and an ortho ester (2-(vinyloxy)-2-phenyl-1,3-dioxolane), and rates of isomerization of this enol to acetaldehyde catalyzed by hydronium and hydroxide ions and formic and acetic acid buffers were measured.Rates of enolization of acetaldehyde, determined by iodine scavenging and catalyzed by hydronium and hydroxide ions, were also measured.These data lead to two concordant, independent determinations of the tautomerization equilibrium constant for acetaldehyde in aqueous solution whose average is KE=(5.89+/-0.81)x10-7, pKE=6.23+/-0.06.They also give KaE=(3.13+/-0.17)x10-11, pKaE=10.50+/-0.02, for the dissociation constant of vinyl alcohol ionizing as an oxygen acid, and KaK=(1.85+/-0.27)x10-17, pKaK=16.73+/-0.06, for the dissociation constant of acetaldehyde ionizing as a carbon acid; all equilibrium constants are concentration quotients and refer to aqueous solution at ionic strength 0.10 M.Kinetic solvent isotope effects on both enolization and ketonization suggest that reaction occurs by a stepwise rather than a concerted mechanism.
Acrolein production by gas-phase glycerol dehydration using PO4/Nb2O5 catalysts
Lee, Kyu Am,Ryoo, HeeKyoung,Ma, Byung Chol,Kim, Youngchul
, p. 1312 - 1315 (2017/12/15)
In this study, modified niobium oxide were prepared to study the addictive effects on the catalytic performance for gas-phase glycerol dehydration. The catalysts were characterized by N2 adsorption/desorption, XRD, NH3-TPD, FT-IR. The amount of phosphoric acid was up to 50 wt% in niobium. As a result, the highest glycerol conversion was achieved over 20 wt% PO4/Nb2O5. It indicates that the optimal amount of phosphoric acid leads the catalyst to have appropriate acidity which is an important factor for gas-phase glycerol dehydration.
Comparative studies of the photocatalytic and microwave -assisted degradation of alizarin red using ZnO/poly(1- naphthylamine) nanohybrids
Riaz, Ufana,Ashraf,Budhiraja, Vaibhav,Aleem, Sadaf,Kashyap, Jyoti
, p. 259 - 267 (2016/01/20)
Semiconductors such as ZnO and TiO2 have been extensively utilized in the photocatalytic degradation of dyes. However till date, no study has been reported to compare the catalytic efficiency of such organic-inorganic hybrids under UV light and microwave irradiation separately. The present work reports the synthesis of poly(1-naphthylamine)/ZnO nanohybrids. The structure and morphology of the synthesized nanocomposites were characterized using FT-IR, UV, XRD, TEM and Cyclic voltammetry analyses. The dye degradation studies were done separately in a photochemical reactor and in laboratory microwave oven and the fragments were identified using LC-MS technique. Results showed that under microwave irradiation, the efficiency of ZnO/PNA as catalyst was higher as compared to UV irradiation. Higher extent of ?OH radical generation was confirmed in microwave as compared to UV irradiation which was found to be responsible for the high rate of degradation of dye solution. A plausible degradation pathway was proposed.
Carbohydrate base co-polymers as an efficient immobilization matrix to enhance lipase activity for potential biocatalytic applications
Badgujar, Kirtikumar Chandulal,Bhanage, Bhalchandra Mahadeo
, p. 709 - 717 (2015/09/02)
In the present study, we have synthesized biocompatible hybrid blend of cellulosic polymers of hydroxypropyl-methyl-cellulose (HPMC) and chitosan (CHY) for the immobilization of Candida rugosa lipase (CRL). The immobilized biocatalyst HPMC:CHY:CRL was subjected for characterization such as SEM, TGA, water content analysis, lipase activity, specific activity and protein content analysis. The kinetic parameter study (Rmax/Km) demonstrated improved biocatalytic activity of lipase after immobilization on carbohydrate co-polymers of HPMC:CHY. This biocatalyst was then employed to study practical biocatalytic applications for kinetic resolution which provided 50% conversion and >94% enantiomeric excess of substrate/product (ees/eep). The protocol demonstrated excellent recyclability upto five cycles. Finally, we studied influence of immobilization on cellulosic polymers for substrate, structure and reactivity for kinetic resolution. Hence, we investigated R0 (initial reaction rate), E-value (enantioselectivity) and Ea (activation energy). This study confirms that, lipase immobilized on carbohydrate polymers had 3-4 folds higher biocatalytic activity as compared to crude CRL.
PROCESS FOR PRODUCTION OF ACROLEIN AND OTHER OXYGENATED COMPOUNDS FROM GLYCEROL IN A TRANSPORTED BED REACTOR
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Page/Page column 9-12, (2008/12/05)
Disclosed is a process for the production of acrolein and other oxygenated compounds from glycerol. Use is made of an acidic catalyst in a moving bed reactor at 200 - 650°C.
Electron transfer between a carbon-centered and nitroxide radicals. A CIDNP study
Ananchenko, Gennady,Fischer, Hanns
, p. 1887 - 1889 (2007/10/03)
A chemically induced dynamic nuclear polarization (CIDNP) study of electron transfer between a carbon-centred and nitroxide radicals was presented. The radicals were generated by laser pulse photolysis of the ketone precursors 2,2,4,4-tetramethylpentan-3-one (di-tert-butyl ketone, 1) for tert-butyl and 2,4-dihydroxy-2,4-dimethylpentan-3-one (di-POH-ketone, 2) for 2-hydroxy-2-propyl (POH) in the absence and in the presence of nitroxides. Results showed that the different rate constants for reaction of tBu and POH with nitroxides reflect different reaction mechanisms.
Photochemical and photophysical regularities of reduction of acetone with triethylamine
Markaryan
, p. 1012 - 1016 (2007/10/03)
The data on chemically induced dynamic polarization of nuclei (CIDPN) obtained in this work and the available data on chemically induced dynamic polarization of electrons (CIDPE) are used to examine photochemical and photophysiscal processes involved in the reduction of acetone by triethylamine (TEA). The time-resolved CIDPN method is used to study the efficiency of TEA as a chemical quencher and the effect of laser radiation intensity (308 nm) on polarization processes and the composition of the reaction products. The relative reactivities of the acetone T1 and S1 states depend on the TEA concentration and the laser irradiation intensity: at [TEA] 1.5 mol/l, singlet acetone molecules are also effectively quenched. At high irradiation intensities, the α-cleavage of triplet acetone also occurs via a two-photon process. The mechanism developed involves reverse proton transfer, disproportionation, and recombination with the participation of radical pairs and agrees with the CIDPN effects observed in experiment.
Photolysis of 2,4-Dihydroxy-2,4-dimethylpentan-3-one Studied by Quantitative Time-resolved CIDNP and Optical Spectroscopy
Salzmann, Michael,Tsentalovich, Yuri P.,Fischer, Hanns
, p. 2119 - 2124 (2007/10/02)
The mechanisms and kinetics of radical reactions induced by pulse photolysis of 2,4-dihydroxy-2,4-dimethylpentane-3-one have been studied by time-resolved chemically induced dynamic nuclear polarization (CIDNP) and optical spectroscopy.The rate constant for the decarbonylation of the 2-hydroxy-2-methylpropanoyl radical is described by A = (8.2 +/- 2.0) * 1011 s-1 and Ea = (23 +/- 3) kJ mol-1 in methanol , and by A = (3.7 +/- 1.0) * 1011 s-1 and Ea = (24 +/- 3) kJ mol-1 in methylcyclopentane solvents and leads to a CIDNP memory effect.Rate constants for the self-termination of the 2-hydroxyprop-2-yl radicals are derived from the second-order time dependence of the multiplet nuclear polarization of the product propan-2-ol.The time dependence of its net nuclear polarization is influenced by electron-nuclear cross-relaxation.The ratios of disproportionation to the combination of radical pairs are also obtained.
Cross-Relaxation and Cross-Correlation Mechanisms Leading to Spin Polarization
Tsentalovich, Yu. P.,Yurkovskaya, A. V.,Frantsev, A. A.,Doctorov, A. B.,Sagdeev, R. Z.
, p. 119 - 130 (2007/10/02)
The photolysis of acetone with various hydrogen donors and of 3-hydroxy-3-methyl-2-butanone involves formation of propan-2-olyl radicals showing both electron and nuclear spin polarizations.The presence of electron polarization in radicals leads to additional CIDNP appearing in reaction products.The transfer of polarization from electron spins to nuclear ones can occur by cross-relaxation and cross-correlation mechanisms.Experimentally, these mechanisms manifest themselves by formation of net CIDNP in symmetrical radical pairs as well as by unusual kinetic behaviour of multiplet CIDNP. - Key words: CIDNP / Kinetics / Radical reactions / Photolysis / Cross relaxation
